dungeoneer/demo/bundle.js

A procedural dungeon generator

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/**
 * Based on Bob Nystrom's procedural dungeon generation logic that he wrote for Hauberk
 * http://journal.stuffwithstuff.com/2014/12/21/rooms-and-mazes/
 */

'use strict';

const Victor = require('victor');
const _ = require('underscore');

const Room = require('./room');
const Tile = require('./tile');

/**
 * @desc The random dungeon generator.
 *
 * Starting with a stage of solid walls, it works like so:
 *
 * 1. Place a number of randomly sized and positioned rooms. If a room
 *    overlaps an existing room, it is discarded. Any remaining rooms are
 *    carved out.
 * 2. Any remaining solid areas are filled in with mazes. The maze generator
 *    will grow and fill in even odd-shaped areas, but will not touch any
 *    rooms.
 * 3. The result of the previous two steps is a series of unconnected rooms
 *    and mazes. We walk the stage and find every tile that can be a
 *    "connector". This is a solid tile that is adjacent to two unconnected
 *    regions.
 * 4. We randomly choose connectors and open them or place a door there until
 *    all of the unconnected regions have been joined. There is also a slight
 *    chance to carve a connector between two already-joined regions, so that
 *    the dungeon isn't single connected.
 * 5. The mazes will have a lot of dead ends. Finally, we remove those by
 *    repeatedly filling in any open tile that's closed on three sides. When
 *    this is done, every corridor in a maze actually leads somewhere.
 *
 * The end result of this is a multiply-connected dungeon with rooms and lots
 * of winding corridors.
 *
 * @constructor
 */
const Dungeon = function Dungeon() {
  var numRoomTries = 50;

  // The inverse chance of adding a connector between two regions that have
  // already been joined. Increasing this leads to more loosely connected
  // dungeons.
  var extraConnectorChance = 50;

  // Increasing this allows rooms to be larger.
  var roomExtraSize = 0;

  var windingPercent = 50;

  var _rooms = [];

  // The index of the current region being carved.
  var _currentRegion = -1;

  var stage;

  const n = new Victor(0, 1);
  const e = new Victor(1, 0);
  const s = new Victor(0, -1);
  const w = new Victor(-1, 0);

  // The four cardinal directions: north, south, east, and west.
  const cardinalDirections = [n, e, s, w];

  const bindStage = givenStage => {
    stage = givenStage;
  };

  let _tiles = [];

  /**
   * @desc returns a tile at the provided coordinates
   *
   * @param {Number} x - The x coordinate to retrieve
   * @param {Number} y - The y coordinate to retrieve
   *
   * @returns {Object} - A Tile object
   */
  const getTile = (x, y) => {
    return _tiles[x][y];
  };

  /**
   * @desc Sets a tile's type and region. This function will thrown an error if
   * the tile doesn't exist.
   *
   * @param {Number} x - The x coordinate of the tile to set
   * @param {Number} y - The y coordinate of the tile to set
   * @param {String} type - The type to set on the tile
   *
   * @returns {Object} - The Tile object or null if the tile was not found
   *
   */
  const setTile = (x, y, type) => {
    if (_tiles[x] && _tiles[x][y]) {
      _tiles[x][y].type = type;
      _tiles[x][y].region = _currentRegion;

      return _tiles[x][y];
    }

    throw new RangeError(`tile at ${x}, ${y} is unreachable`);
  };

  /**
   * @desc Generates tile data to the dimension of the stage.
   *
   * @param {String} type - The tile type to set on newly created tiles
   *
   * @returns {Array} - The _tiles array
   */
  const fill = type => {
    let neighbours = [];
    let nesw = {};
    var x;
    var y;

    for (x = 0; x < stage.width; x++) {
      _tiles.push([]);
      for (y = 0; y < stage.height; y++) {
        _tiles[x].push(new Tile(type));
      }
    }

    for (x = 0; x < stage.width; x++) {
      for (y = 0; y < stage.height; y++) {
        neighbours = [];
        nesw = {};
        if (_tiles[x][y - 1]) {
          neighbours.push(_tiles[x][y - 1]);
          nesw.north = _tiles[x][y - 1];
        }
        if (_tiles[x + 1] && _tiles[x + 1][y - 1]) {
          neighbours.push(_tiles[x + 1][y - 1]);
        }
        if (_tiles[x + 1] && _tiles[x + 1][y]) {
          neighbours.push(_tiles[x + 1][y]);
          nesw.east = _tiles[x + 1][y];
        }
        if (_tiles[x + 1] && _tiles[x + 1][y + 1]) {
          neighbours.push(_tiles[x + 1][y + 1]);
        }
        if (_tiles[x] && _tiles[x][y + 1]) {
          neighbours.push(_tiles[x][y + 1]);
          nesw.south = _tiles[x][y + 1];
        }
        if (_tiles[x - 1] && _tiles[x - 1][y + 1]) {
          neighbours.push(_tiles[x - 1][y + 1]);
        }
        if (_tiles[x - 1] && _tiles[x - 1][y]) {
          neighbours.push(_tiles[x - 1][y]);
          nesw.west = _tiles[x - 1][y];
        }
        if (_tiles[x - 1] && _tiles[x - 1][y - 1]) {
          neighbours.push(_tiles[x - 1][y - 1]);
        }
        _tiles[x][y].setNeighbours(neighbours);
        _tiles[x][y].nesw = nesw;
      }
    }

    return _tiles;
  };

  /**
   * @desc Master function for generating a dungeon
   *
   * @param {Object} stage - An object with a width key and a height key. Used
   * to determine the size of the dungeon. Must be odd with and height.
   * @param {Boolean} debug - outputs debug info if set to true
   *
   * @returns {Object} - Tile information for the dungeon
   */
  const generate = (stage, debug = false) => {
    let startDate = Date.now();
    if (stage.width % 2 === 0 || stage.height % 2 === 0) {
      throw new Error('The stage must be odd-sized.');
    }

    bindStage(stage);

    fill('wall');

    _addRooms();

    // Fill in all of the empty space with mazes.
    for (var y = 1; y < stage.height; y += 2) {
      for (var x = 1; x < stage.width; x += 2) {
        // Skip the maze generation if the tile is already carved
        if (getTile(x, y).type === 'floor') {
          continue;
        }
        _growMaze(x, y);
      }
    }

    _connectRegions();

    _removeDeadEnds();

    let endDate = Date.now();

    if (debug) {
      console.log('Dungeon generated in ' + (endDate - startDate) + 'ms');
    }

    return {
      rooms: _rooms,
      tiles: _tiles
    };
  };

  /**
   * @desc Implementation of the "growing tree" algorithm from here:
   * http://www.astrolog.org/labyrnth/algrithm.htm.
   *
   * @param {Number} startX - The x coordinate to start at
   * @param {Number} startY - The y coordinate to start at
   *
   * @returns {void}
   */
  const _growMaze = (startX, startY) => {
    var cells = [];
    var lastDir;

    if (_tiles[startX][startY].neighbours.filter(x => x.type === 'floor').length > 0) {
      return;
    }

    _startRegion();

    _carve(startX, startY);

    cells.push(new Victor(startX, startY));

    let count = 0;

    while (cells.length && count < 500) {
      count++;
      var cell = cells[cells.length - 1];

      // See which adjacent cells are open.
      var unmadeCells = [];

      for (let dir of cardinalDirections) {
        if (_canCarve(cell, dir)) {
          unmadeCells.push(dir);
        }
      }

      if (unmadeCells.length) {
        // Based on how "windy" passages are, try to prefer carving in the
        // same direction.
        var dir;
        var stringifiedCells = unmadeCells.map(v => v.toString());
        if (lastDir && stringifiedCells.indexOf(lastDir.toString()) > -1 && _.random(1, 100) > windingPercent) {
          dir = lastDir.clone();
        } else {
          let rand = _.random(0, unmadeCells.length - 1);
          dir = unmadeCells[rand].clone();
        }

        let carveLoc1 = cell.clone().add(dir).toObject();
        _carve(carveLoc1.x, carveLoc1.y);

        let carveLoc2 = cell.clone().add(dir).add(dir).toObject();
        _carve(carveLoc2.x, carveLoc2.y);

        cells.push(cell.clone().add(dir).add(dir));

        lastDir = dir.clone();
      } else {
        // No adjacent uncarved cells.
        cells.pop();

        // This path has ended.
        lastDir = null;
      }
    }
  };

  /**
   * @desc Creates rooms in the dungeon by repeatedly creating random rooms and
   * seeing if they overlap. Rooms that overlap are discarded. This process is
   * repeated until it hits the maximum tries determined by the 'numRoomTries'
   * variable.
   *
   * @returns {void}
   */
  const _addRooms = () => {
    for (var i = 0; i < numRoomTries; i++) {
      // Pick a random room size. The funny math here does two things:
      // - It makes sure rooms are odd-sized to line up with maze.
      // - It avoids creating rooms that are too rectangular: too tall and
      //   narrow or too wide and flat.
      var size = _.random(1, 3 + roomExtraSize) * 2 + 1;
      var rectangularity = _.random(0, 1 + Math.floor(size / 2)) * 2;
      var width = size;
      var height = size;
      if (_oneIn(2)) {
        width += rectangularity;
      } else {
        height += rectangularity;
      }

      var x = _.random(0, Math.floor((stage.width - width) / 2)) * 2 + 1;
      var y = _.random(0, Math.floor((stage.height - height) / 2)) * 2 + 1;

      if (x > stage.width - width) {
        x = stage.width - width - 1;
      }

      if (y > stage.height - height) {
        y = stage.height - height - 1;
      }

      var room = new Room(x, y, width, height);

      var overlaps = false;

      for (var other of _rooms) {
        if (room.intersects(other)) {
          overlaps = true;
          break;
        }
      }

      if (overlaps) {
        continue;
      }

      _rooms.push(room);

      _startRegion();

      // Convert room tiles to floor
      carveArea(x, y, width, height);
    }
  };

  /**
   * @desc converts an area of tiles to floor type
   *
   * @param {Number} x - The starting x coordinate
   * @param {Number} y - The starting y coordinate
   * @param {Number} width - The width of the area to carve
   * @param {Number} height - The height of the area to carve
   *
   * @returns {void}
   */
  const carveArea = (x, y, width, height) => {
    for (var i = x; i < x + width; i++) {
      for (var j = y; j < y + height; j++) {
        _carve(i, j);
      }
    }
  };

  /**
   * @desc Creates doorways between each generated region of tiles
   *
   * @return {void}
   */
  const _connectRegions = () => {
    let regionConnections = {};
    _tiles.forEach(row => {
      row.forEach(tile => {
        if (tile.type === 'floor') {
          return;
        }

        let tileRegions = _.unique(_.values(tile.nesw).map(x => x.region).filter(x => !_.isUndefined(x)));
        if (tileRegions.length <= 1) {
          return;
        }

        let key = tileRegions.join('-');
        if (!regionConnections[key]) {
          regionConnections[key] = [];
        }
        regionConnections[key].push(tile);
      });
    });

    _.each(regionConnections, connections => {
      let index = _.random(0, connections.length - 1);
      connections[index].type = 'door';
      connections.splice(index, 1);

      // Occasional open up additional connections
      connections.forEach(conn => {
        if (_oneIn(extraConnectorChance)) {
          conn.type = 'door';
        }
      });
    });
  };

  /**
   * @desc Helper function for calculating random chance. The higher the number
   * provided the less likely this value is to return true.
   *
   * @param {Number} num - The ceiling number that could be calculated
   *
   * @returns {Boolean} - True if the function rolled a one
   *
   * @example
   * _oneIn(50); // - Has a 1 in 50 chance of returning true
   */
  const _oneIn = num => {
    return _.random(1, num) === 1;
  };

  /**
   * @desc Fills in dead ends in the dungeon with wall tiles
   *
   * @returns {void}
   */
  const _removeDeadEnds = () => {
    var done = false;

    const cycle = () => {
      let done = true;
      _tiles.forEach(row => {
        row.forEach(tile => {
          // If it only has one exit, it's a dead end --> fill it in!
          if (tile.type === 'wall') {
            return;
          }
          if (_.values(tile.nesw).filter(t => t.type !== 'wall').length <= 1) {
            tile.type = 'wall';
            done = false;
          }
        });
      });

      return done;
    };

    while (!done) {
      done = true;
      done = cycle();
    }
  };

  /**
   * @desc Gets whether or not an opening can be carved from the given starting
   * [Cell] at [pos] to the adjacent Cell facing [direction]. Returns `true`
   * if the starting Cell is in bounds and the destination Cell is filled
   * (or out of bounds).</returns>
   *
   * @param {Victor} cell - Victor JS vector object
   * @param {Victor} direction - Victor JS vector object indicating direction
   *
   * @return {Boolean} - true if the path can be carved
   */
  const _canCarve = (cell, direction) => {
    // Must end in bounds.
    let end = cell.clone().add(direction).add(direction).add(direction).toObject();

    if (!_tiles[end.x] || !_tiles[end.x][end.y]) {
      return false;
    }

    if (getTile(end.x, end.y).type !== 'wall') {
      return false;
    }

    // Destination must not be open.
    let dest = cell.clone().add(direction).add(direction).toObject();
    return getTile(dest.x, dest.y).type !== 'floor';
  };

  /**
   * @desc Increments the current region. Typically called every time a new area
   * starts being carved
   *
   * @returns {Number} - The current region number
   */
  const _startRegion = () => {
    _currentRegion++;
    return _currentRegion;
  };

  /**
   * @desc Changes the Tile at a given coordinate to a provided type. Typically
   * used to change the type to 'floor'
   *
   * @param {Number} x - The x coordinate to change
   * @param {Number} y - The y coordinate to change
   * @param {String} type - The type to change the tile to. Defaults to 'floor'
   *
   * @returns {void}
   */
  const _carve = (x, y, type = 'floor') => {
    setTile(x, y, type);
  };

  return {
    generate
  };
};

const generate = options => {
  return new Dungeon().generate(options);
};

module.exports = {
  generate
};

},{"./room":2,"./tile":3,"underscore":4,"victor":5}],2:[function(require,module,exports){
'use strict';

/**
 * @desc Helper class for drawing rooms when generating dungeons
 * @constructor
 *
 * @param {Number} x - The x coordinate of the top side of the room
 * @param {Number} y - The y coordinate of the left hand side of the room
 * @param {Number} width - The width of the room
 * @param {Number} height - The height of the room
 */

const Room = function Room(x, y, width, height) {
  this.x = x;
  this.y = y;
  this.width = width;
  this.height = height;
};

/**
 * @desc Returns the bounding box for this room
 * @function
 *
 * @returns {Object} - Bounding box object containing a top, right, bottom and
 * left value.
 */
Room.prototype.getBoundingBox = function getBoundingBox() {
  return {
    top: this.y,
    right: this.x + this.width,
    bottom: this.y + this.height,
    left: this.x
  };
};

/**
 * @desc Compares this room with an entity that has a bounding box method to see
 * if they intersect.
 *
 * @param {Object} other - An object with a getBoundingBox() method
 *
 * @returns {Boolean} - true if there is an intersection
 */
Room.prototype.intersects = function intersects(other) {
  if (!other.getBoundingBox) {
    throw new Error('Given entity has no method getBoundingBox');
  }
  var r1 = this.getBoundingBox();
  var r2 = other.getBoundingBox();

  return !(r2.left > r1.right || r2.right < r1.left || r2.top > r1.bottom || r2.bottom < r1.top);
};

module.exports = Room;

},{}],3:[function(require,module,exports){
'use strict';

/**
 * @desc Class for a single tilein a dungeon
 * @constructor
 *
 * @param {String} type - The type of tile, e.g. 'wall', 'floor'
 */

const Tile = function Tile(type) {
  this.type = type;
  this.neighbours = [];
};

/**
 * @desc Sets an array containing this tiles immediate neighbours
 *
 * @param {Object[]} neighbours - An array of neighbouring Tiles
 *
 * @return {Object} - returns the Tile object, useful for chaining
 */
Tile.prototype.setNeighbours = function (neighbours) {
  this.neighbours = neighbours;
  return this;
};

module.exports = Tile;

},{}],4:[function(require,module,exports){
(function (global){
//     Underscore.js 1.9.1
//     http://underscorejs.org
//     (c) 2009-2018 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
//     Underscore may be freely distributed under the MIT license.

(function() {

  // Baseline setup
  // --------------

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  // Collection Functions
  // --------------------

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      var keys = _.keys(obj);
      for (i = 0, length = keys.length; i < length; i++) {
        iteratee(obj[keys[i]], keys[i], obj);
      }
    }
    return obj;
  };

  // Return the results of applying the iteratee to each element.
  _.map = _.collect = function(obj, iteratee, context) {
    iteratee = cb(iteratee, context);
    var keys = !isArrayLike(obj) && _.keys(obj),
        length = (keys || obj).length,
        results = Array(length);
    for (var index = 0; index < length; index++) {
      var currentKey = keys ? keys[index] : index;
      results[index] = iteratee(obj[currentKey], currentKey, obj);
    }
    return results;
  };

  // Create a reducing function iterating left or right.
  var createReduce = function(dir) {
    // Wrap code that reassigns argument variables in a separate function than
    // the one that accesses `arguments.length` to avoid a perf hit. (#1991)
    var reducer = function(obj, iteratee, memo, initial) {
      var keys = !isArrayLike(obj) && _.keys(obj),
          length = (keys || obj).length,
          index = dir > 0 ? 0 : length - 1;
      if (!initial) {
        memo = obj[keys ? keys[index] : index];
        index += dir;
      }
      for (; index >= 0 && index < length; index += dir) {
        var currentKey = keys ? keys[index] : index;
        memo = iteratee(memo, obj[currentKey], currentKey, obj);
      }
      return memo;
    };

    return function(obj, iteratee, memo, context) {
      var initial = arguments.length >= 3;
      return reducer(obj, optimizeCb(iteratee, context, 4), memo, initial);
    };
  };

  // **Reduce** builds up a single result from a list of values, aka `inject`,
  // or `foldl`.
  _.reduce = _.foldl = _.inject = createReduce(1);

  // The right-associative version of reduce, also known as `foldr`.
  _.reduceRight = _.foldr = createReduce(-1);

  // Return the first value which passes a truth test. Aliased as `detect`.
  _.find = _.detect = function(obj, predicate, context) {
    var keyFinder = isArrayLike(obj) ? _.findIndex : _.findKey;
    var key = keyFinder(obj, predicate, context);
    if (key !== void 0 && key !== -1) return obj[key];
  };

  // Return all the elements that pass a truth test.
  // Aliased as `select`.
  _.filter = _.select = function(obj, predicate, context) {
    var results = [];
    predicate = cb(predicate, context);
    _.each(obj, function(value, index, list) {
      if (predicate(value, index, list)) results.push(value);
    });
    return results;
  };

  // Return all the elements for which a truth test fails.
  _.reject = function(obj, predicate, context) {
    return _.filter(obj, _.negate(cb(predicate)), context);
  };

  // Determine whether all of the elements match a truth test.
  // Aliased as `all`.
  _.every = _.all = function(obj, predicate, context) {
    predicate = cb(predicate, context);
    var keys = !isArrayLike(obj) && _.keys(obj),
        length = (keys || obj).length;
    for (var index = 0; index < length; index++) {
      var currentKey = keys ? keys[index] : index;
      if (!predicate(obj[currentKey], currentKey, obj)) return false;
    }
    return true;
  };

  // Determine if at least one element in the object matches a truth test.
  // Aliased as `any`.
  _.some = _.any = function(obj, predicate, context) {
    predicate = cb(predicate, context);
    var keys = !isArrayLike(obj) && _.keys(obj),
        length = (keys || obj).length;
    for (var index = 0; index < length; index++) {
      var currentKey = keys ? keys[index] : index;
      if (predicate(obj[currentKey], currentKey, obj)) return true;
    }
    return false;
  };

  // Determine if the array or object contains a given item (using `===`).
  // Aliased as `includes` and `include`.
  _.contains = _.includes = _.include = function(obj, item, fromIndex, guard) {
    if (!isArrayLike(obj)) obj = _.values(obj);
    if (typeof fromIndex != 'number' || guard) fromIndex = 0;
    return _.indexOf(obj, item, fromIndex) >= 0;
  };

  // Invoke a method (with arguments) on every item in a collection.
  _.invoke = restArguments(function(obj, path, args) {
    var contextPath, func;
    if (_.isFunction(path)) {
      func = path;
    } else if (_.isArray(path)) {
      contextPath = path.slice(0, -1);
      path = path[path.length - 1];
    }
    return _.map(obj, function(context) {
      var method = func;
      if (!method) {
        if (contextPath && contextPath.length) {
          context = deepGet(context, contextPath);
        }
        if (context == null) return void 0;
        method = context[path];
      }
      return method == null ? method : method.apply(context, args);
    });
  });

  // Convenience version of a common use case of `map`: fetching a property.
  _.pluck = function(obj, key) {
    return _.map(obj, _.property(key));
  };

  // Convenience version of a common use case of `filter`: selecting only objects
  // containing specific `key:value` pairs.
  _.where = function(obj, attrs) {
    return _.filter(obj, _.matcher(attrs));
  };

  // Convenience version of a common use case of `find`: getting the first object
  // containing specific `key:value` pairs.
  _.findWhere = function(obj, attrs) {
    return _.find(obj, _.matcher(attrs));
  };

  // Return the maximum element (or element-based computation).
  _.max = function(obj, iteratee, context) {
    var result = -Infinity, lastComputed = -Infinity,
        value, computed;
    if (iteratee == null || typeof iteratee == 'number' && typeof obj[0] != 'object' && obj != null) {
      obj = isArrayLike(obj) ? obj : _.values(obj);
      for (var i = 0, length = obj.length; i < length; i++) {
        value = obj[i];
        if (value != null && value > result) {
          result = value;
        }
      }
    } else {
      iteratee = cb(iteratee, context);
      _.each(obj, function(v, index, list) {
        computed = iteratee(v, index, list);
        if (computed > lastComputed || computed === -Infinity && result === -Infinity) {
          result = v;
          lastComputed = computed;
        }
      });
    }
    return result;
  };

  // Return the minimum element (or element-based computation).
  _.min = function(obj, iteratee, context) {
    var result = Infinity, lastComputed = Infinity,
        value, computed;
    if (iteratee == null || typeof iteratee == 'number' && typeof obj[0] != 'object' && obj != null) {
      obj = isArrayLike(obj) ? obj : _.values(obj);
      for (var i = 0, length = obj.length; i < length; i++) {
        value = obj[i];
        if (value != null && value < result) {
          result = value;
        }
      }
    } else {
      iteratee = cb(iteratee, context);
      _.each(obj, function(v, index, list) {
        computed = iteratee(v, index, list);
        if (computed < lastComputed || computed === Infinity && result === Infinity) {
          result = v;
          lastComputed = computed;
        }
      });
    }
    return result;
  };

  // Shuffle a collection.
  _.shuffle = function(obj) {
    return _.sample(obj, Infinity);
  };

  // Sample **n** random values from a collection using the modern version of the
  // [Fisher-Yates shuffle](http://en.wikipedia.org/wiki/Fisher–Yates_shuffle).
  // If **n** is not specified, returns a single random element.
  // The internal `guard` argument allows it to work with `map`.
  _.sample = function(obj, n, guard) {
    if (n == null || guard) {
      if (!isArrayLike(obj)) obj = _.values(obj);
      return obj[_.random(obj.length - 1)];
    }
    var sample = isArrayLike(obj) ? _.clone(obj) : _.values(obj);
    var length = getLength(sample);
    n = Math.max(Math.min(n, length), 0);
    var last = length - 1;
    for (var index = 0; index < n; index++) {
      var rand = _.random(index, last);
      var temp = sample[index];
      sample[index] = sample[rand];
      sample[rand] = temp;
    }
    return sample.slice(0, n);
  };

  // Sort the object's values by a criterion produced by an iteratee.
  _.sortBy = function(obj, iteratee, context) {
    var index = 0;
    iteratee = cb(iteratee, context);
    return _.pluck(_.map(obj, function(value, key, list) {
      return {
        value: value,
        index: index++,
        criteria: iteratee(value, key, list)
      };
    }).sort(function(left, right) {
      var a = left.criteria;
      var b = right.criteria;
      if (a !== b) {
        if (a > b || a === void 0) return 1;
        if (a < b || b === void 0) return -1;
      }
      return left.index - right.index;
    }), 'value');
  };

  // An internal function used for aggregate "group by" operations.
  var group = function(behavior, partition) {
    return function(obj, iteratee, context) {
      var result = partition ? [[], []] : {};
      iteratee = cb(iteratee, context);
      _.each(obj, function(value, index) {
        var key = iteratee(value, index, obj);
        behavior(result, value, key);
      });
      return result;
    };
  };

  // Groups the object's values by a criterion. Pass either a string attribute
  // to group by, or a function that returns the criterion.
  _.groupBy = group(function(result, value, key) {
    if (has(result, key)) result[key].push(value); else result[key] = [value];
  });

  // Indexes the object's values by a criterion, similar to `groupBy`, but for
  // when you know that your index values will be unique.
  _.indexBy = group(function(result, value, key) {
    result[key] = value;
  });

  // Counts instances of an object that group by a certain criterion. Pass
  // either a string attribute to count by, or a function that returns the
  // criterion.
  _.countBy = group(function(result, value, key) {
    if (has(result, key)) result[key]++; else result[key] = 1;
  });

  var reStrSymbol = /[^\ud800-\udfff]|[\ud800-\udbff][\udc00-\udfff]|[\ud800-\udfff]/g;
  // Safely create a real, live array from anything iterable.
  _.toArray = function(obj) {
    if (!obj) return [];
    if (_.isArray(obj)) return slice.call(obj);
    if (_.isString(obj)) {
      // Keep surrogate pair characters together
      return obj.match(reStrSymbol);
    }
    if (isArrayLike(obj)) return _.map(obj, _.identity);
    return _.values(obj);
  };

  // Return the number of elements in an object.
  _.size = function(obj) {
    if (obj == null) return 0;
    return isArrayLike(obj) ? obj.length : _.keys(obj).length;
  };

  // Split a collection into two arrays: one whose elements all satisfy the given
  // predicate, and one whose elements all do not satisfy the predicate.
  _.partition = group(function(result, value, pass) {
    result[pass ? 0 : 1].push(value);
  }, true);

  // Array Functions
  // ---------------

  // Get the first element of an array. Passing **n** will return the first N
  // values in the array. Aliased as `head` and `take`. The **guard** check
  // allows it to work with `_.map`.
  _.first = _.head = _.take = function(array, n, guard) {
    if (array == null || array.length < 1) return n == null ? void 0 : [];
    if (n == null || guard) return array[0];
    return _.initial(array, array.length - n);
  };

  // Returns everything but the last entry of the array. Especially useful on
  // the arguments object. Passing **n** will return all the values in
  // the array, excluding the last N.
  _.initial = function(array, n, guard) {
    return slice.call(array, 0, Math.max(0, array.length - (n == null || guard ? 1 : n)));
  };

  // Get the last element of an array. Passing **n** will return the last N
  // values in the array.
  _.last = function(array, n, guard) {
    if (array == null || array.length < 1) return n == null ? void 0 : [];
    if (n == null || guard) return array[array.length - 1];
    return _.rest(array, Math.max(0, array.length - n));
  };

  // Returns everything but the first entry of the array. Aliased as `tail` and `drop`.
  // Especially useful on the arguments object. Passing an **n** will return
  // the rest N values in the array.
  _.rest = _.tail = _.drop = function(array, n, guard) {
    return slice.call(array, n == null || guard ? 1 : n);
  };

  // Trim out all falsy values from an array.
  _.compact = function(array) {
    return _.filter(array, Boolean);
  };

  // Internal implementation of a recursive `flatten` function.
  var flatten = function(input, shallow, strict, output) {
    output = output || [];
    var idx = output.length;
    for (var i = 0, length = getLength(input); i < length; i++) {
      var value = input[i];
      if (isArrayLike(value) && (_.isArray(value) || _.isArguments(value))) {
        // Flatten current level of array or arguments object.
        if (shallow) {
          var j = 0, len = value.length;
          while (j < len) output[idx++] = value[j++];
        } else {
          flatten(value, shallow, strict, output);
          idx = output.length;
        }
      } else if (!strict) {
        output[idx++] = value;
      }
    }
    return output;
  };

  // Flatten out an array, either recursively (by default), or just one level.
  _.flatten = function(array, shallow) {
    return flatten(array, shallow, false);
  };

  // Return a version of the array that does not contain the specified value(s).
  _.without = restArguments(function(array, otherArrays) {
    return _.difference(array, otherArrays);
  });

  // Produce a duplicate-free version of the array. If the array has already
  // been sorted, you have the option of using a faster algorithm.
  // The faster algorithm will not work with an iteratee if the iteratee
  // is not a one-to-one function, so providing an iteratee will disable
  // the faster algorithm.
  // Aliased as `unique`.
  _.uniq = _.unique = function(array, isSorted, iteratee, context) {
    if (!_.isBoolean(isSorted)) {
      context = iteratee;
      iteratee = isSorted;
      isSorted = false;
    }
    if (iteratee != null) iteratee = cb(iteratee, context);
    var result = [];
    var seen = [];
    for (var i = 0, length = getLength(array); i < length; i++) {
      var value = array[i],
          computed = iteratee ? iteratee(value, i, array) : value;
      if (isSorted && !iteratee) {
        if (!i || seen !== computed) result.push(value);
        seen = computed;
      } else if (iteratee) {
        if (!_.contains(seen, computed)) {
          seen.push(computed);
          result.push(value);
        }
      } else if (!_.contains(result, value)) {
        result.push(value);
      }
    }
    return result;
  };

  // Produce an array that contains the union: each distinct element from all of
  // the passed-in arrays.
  _.union = restArguments(function(arrays) {
    return _.uniq(flatten(arrays, true, true));
  });

  // Produce an array that contains every item shared between all the
  // passed-in arrays.
  _.intersection = function(array) {
    var result = [];
    var argsLength = arguments.length;
    for (var i = 0, length = getLength(array); i < length; i++) {
      var item = array[i];
      if (_.contains(result, item)) continue;
      var j;
      for (j = 1; j < argsLength; j++) {
        if (!_.contains(arguments[j], item)) break;
      }
      if (j === argsLength) result.push(item);
    }
    return result;
  };

  // Take the difference between one array and a number of other arrays.
  // Only the elements present in just the first array will remain.
  _.difference = restArguments(function(array, rest) {
    rest = flatten(rest, true, true);
    return _.filter(array, function(value){
      return !_.contains(rest, value);
    });
  });

  // Complement of _.zip. Unzip accepts an array of arrays and groups
  // each array's elements on shared indices.
  _.unzip = function(array) {
    var length = array && _.max(array, getLength).length || 0;
    var result = Array(length);

    for (var index = 0; index < length; index++) {
      result[index] = _.pluck(array, index);
    }
    return result;
  };

  // Zip together multiple lists into a single array -- elements that share
  // an index go together.
  _.zip = restArguments(_.unzip);

  // Converts lists into objects. Pass either a single array of `[key, value]`
  // pairs, or two parallel arrays of the same length -- one of keys, and one of
  // the corresponding values. Passing by pairs is the reverse of _.pairs.
  _.object = function(list, values) {
    var result = {};
    for (var i = 0, length = getLength(list); i < length; i++) {
      if (values) {
        result[list[i]] = values[i];
      } else {
        result[list[i][0]] = list[i][1];
      }
    }
    return result;
  };

  // Generator function to create the findIndex and findLastIndex functions.
  var createPredicateIndexFinder = function(dir) {
    return function(array, predicate, context) {
      predicate = cb(predicate, context);
      var length = getLength(array);
      var index = dir > 0 ? 0 : length - 1;
      for (; index >= 0 && index < length; index += dir) {
        if (predicate(array[index], index, array)) return index;
      }
      return -1;
    };
  };

  // Returns the first index on an array-like that passes a predicate test.
  _.findIndex = createPredicateIndexFinder(1);
  _.findLastIndex = createPredicateIndexFinder(-1);

  // Use a comparator function to figure out the smallest index at which
  // an object should be inserted so as to maintain order. Uses binary search.
  _.sortedIndex = function(array, obj, iteratee, context) {
    iteratee = cb(iteratee, context, 1);
    var value = iteratee(obj);
    var low = 0, high = getLength(array);
    while (low < high) {
      var mid = Math.floor((low + high) / 2);
      if (iteratee(array[mid]) < value) low = mid + 1; else high = mid;
    }
    return low;
  };

  // Generator function to create the indexOf and lastIndexOf functions.
  var createIndexFinder = function(dir, predicateFind, sortedIndex) {
    return function(array, item, idx) {
      var i = 0, length = getLength(array);
      if (typeof idx == 'number') {
        if (dir > 0) {
          i = idx >= 0 ? idx : Math.max(idx + length, i);
        } else {
          length = idx >= 0 ? Math.min(idx + 1, length) : idx + length + 1;
        }
      } else if (sortedIndex && idx && length) {
        idx = sortedIndex(array, item);
        return array[idx] === item ? idx : -1;
      }
      if (item !== item) {
        idx = predicateFind(slice.call(array, i, length), _.isNaN);
        return idx >= 0 ? idx + i : -1;
      }
      for (idx = dir > 0 ? i : length - 1; idx >= 0 && idx < length; idx += dir) {
        if (array[idx] === item) return idx;
      }
      return -1;
    };
  };

  // Return the position of the first occurrence of an item in an array,
  // or -1 if the item is not included in the array.
  // If the array is large and already in sort order, pass `true`
  // for **isSorted** to use binary search.
  _.indexOf = createIndexFinder(1, _.findIndex, _.sortedIndex);
  _.lastIndexOf = createIndexFinder(-1, _.findLastIndex);

  // Generate an integer Array containing an arithmetic progression. A port of
  // the native Python `range()` function. See
  // [the Python documentation](http://docs.python.org/library/functions.html#range).
  _.range = function(start, stop, step) {
    if (stop == null) {
      stop = start || 0;
      start = 0;
    }
    if (!step) {
      step = stop < start ? -1 : 1;
    }

    var length = Math.max(Math.ceil((stop - start) / step), 0);
    var range = Array(length);

    for (var idx = 0; idx < length; idx++, start += step) {
      range[idx] = start;
    }

    return range;
  };

  // Chunk a single array into multiple arrays, each containing `count` or fewer
  // items.
  _.chunk = function(array, count) {
    if (count == null || count < 1) return [];
    var result = [];
    var i = 0, length = array.length;
    while (i < length) {
      result.push(slice.call(array, i, i += count));
    }
    return result;
  };

  // Function (ahem) Functions
  // ------------------

  // Determines whether to execute a function as a constructor
  // or a normal function with the provided arguments.
  var executeBound = function(sourceFunc, boundFunc, context, callingContext, args) {
    if (!(callingContext instanceof boundFunc)) return sourceFunc.apply(context, args);
    var self = baseCreate(sourceFunc.prototype);
    var result = sourceFunc.apply(self, args);
    if (_.isObject(result)) return result;
    return self;
  };

  // Create a function bound to a given object (assigning `this`, and arguments,
  // optionally). Delegates to **ECMAScript 5**'s native `Function.bind` if
  // available.
  _.bind = restArguments(function(func, context, args) {
    if (!_.isFunction(func)) throw new TypeError('Bind must be called on a function');
    var bound = restArguments(function(callArgs) {
      return executeBound(func, bound, context, this, args.concat(callArgs));
    });
    return bound;
  });

  // Partially apply a function by creating a version that has had some of its
  // arguments pre-filled, without changing its dynamic `this` context. _ acts
  // as a placeholder by default, allowing any combination of arguments to be
  // pre-filled. Set `_.partial.placeholder` for a custom placeholder argument.
  _.partial = restArguments(function(func, boundArgs) {
    var placeholder = _.partial.placeholder;
    var bound = function() {
      var position = 0, length = boundArgs.length;
      var args = Array(length);
      for (var i = 0; i < length; i++) {
        args[i] = boundArgs[i] === placeholder ? arguments[position++] : boundArgs[i];
      }
      while (position < arguments.length) args.push(arguments[position++]);
      return executeBound(func, bound, this, this, args);
    };
    return bound;
  });

  _.partial.placeholder = _;

  // Bind a number of an object's methods to that object. Remaining arguments
  // are the method names to be bound. Useful for ensuring that all callbacks
  // defined on an object belong to it.
  _.bindAll = restArguments(function(obj, keys) {
    keys = flatten(keys, false, false);
    var index = keys.length;
    if (index < 1) throw new Error('bindAll must be passed function names');
    while (index--) {
      var key = keys[index];
      obj[key] = _.bind(obj[key], obj);
    }
  });

  // Memoize an expensive function by storing its results.
  _.memoize = function(func, hasher) {
    var memoize = function(key) {
      var cache = memoize.cache;
      var address = '' + (hasher ? hasher.apply(this, arguments) : key);
      if (!has(cache, address)) cache[address] = func.apply(this, arguments);
      return cache[address];
    };
    memoize.cache = {};
    return memoize;
  };

  // Delays a function for the given number of milliseconds, and then calls
  // it with the arguments supplied.
  _.delay = restArguments(function(func, wait, args) {
    return setTimeout(function() {
      return func.apply(null, args);
    }, wait);
  });

  // Defers a function, scheduling it to run after the current call stack has
  // cleared.
  _.defer = _.partial(_.delay, _, 1);

  // Returns a function, that, when invoked, will only be triggered at most once
  // during a given window of time. Normally, the throttled function will run
  // as much as it can, without ever going more than once per `wait` duration;
  // but if you'd like to disable the execution on the leading edge, pass
  // `{leading: false}`. To disable execution on the trailing edge, ditto.
  _.throttle = function(func, wait, options) {
    var timeout, context, args, result;
    var previous = 0;
    if (!options) options = {};

    var later = function() {
      previous = options.leading === false ? 0 : _.now();
      timeout = null;
      result = func.apply(context, args);
      if (!timeout) context = args = null;
    };

    var throttled = function() {
      var now = _.now();
      if (!previous && options.leading === false) previous = now;
      var remaining = wait - (now - previous);
      context = this;
      args = arguments;
      if (remaining <= 0 || remaining > wait) {
        if (timeout) {
          clearTimeout(timeout);
          timeout = null;
        }
        previous = now;
        result = func.apply(context, args);
        if (!timeout) context = args = null;
      } else if (!timeout && options.trailing !== false) {
        timeout = setTimeout(later, remaining);
      }
      return result;
    };

    throttled.cancel = function() {
      clearTimeout(timeout);
      previous = 0;
      timeout = context = args = null;
    };

    return throttled;
  };

  // Returns a function, that, as long as it continues to be invoked, will not
  // be triggered. The function will be called after it stops being called for
  // N milliseconds. If `immediate` is passed, trigger the function on the
  // leading edge, instead of the trailing.
  _.debounce = function(func, wait, immediate) {
    var timeout, result;

    var later = function(context, args) {
      timeout = null;
      if (args) result = func.apply(context, args);
    };

    var debounced = restArguments(function(args) {
      if (timeout) clearTimeout(timeout);
      if (immediate) {
        var callNow = !timeout;
        timeout = setTimeout(later, wait);
        if (callNow) result = func.apply(this, args);
      } else {
        timeout = _.delay(later, wait, this, args);
      }

      return result;
    });

    debounced.cancel = function() {
      clearTimeout(timeout);
      timeout = null;
    };

    return debounced;
  };

  // Returns the first function passed as an argument to the second,
  // allowing you to adjust arguments, run code before and after, and
  // conditionally execute the original function.
  _.wrap = function(func, wrapper) {
    return _.partial(wrapper, func);
  };

  // Returns a negated version of the passed-in predicate.
  _.negate = function(predicate) {
    return function() {
      return !predicate.apply(this, argumen