mathjs/src/function/matrix/map.js

Math.js is an extensive math library for JavaScript and Node.js. It features a flexible expression parser with support for symbolic computation, comes with a large set of built-in functions and constants, and offers an integrated solution to work with dif

'use strict'

const maxArgumentCount = require('../../utils/function').maxArgumentCount

function factory (type, config, load, typed) {
  /**
   * Create a new matrix or array with the results of the callback function executed on
   * each entry of the matrix/array.
   *
   * Syntax:
   *
   *    math.map(x, callback)
   *
   * Examples:
   *
   *    math.map([1, 2, 3], function(value) {
   *      return value * value
   *    })  // returns [1, 4, 9]
   *
   * See also:
   *
   *    filter, forEach, sort
   *
   * @param {Matrix | Array} x    The matrix to iterate on.
   * @param {Function} callback   The callback method is invoked with three
   *                              parameters: the value of the element, the index
   *                              of the element, and the matrix being traversed.
   * @return {Matrix | array}     Transformed map of x
   */
  const map = typed('map', {
    'Array, function': _map,

    'Matrix, function': function (x, callback) {
      return x.map(callback)
    }
  })

  map.toTex = undefined // use default template

  return map
}

/**
 * Map for a multi dimensional array
 * @param {Array} array
 * @param {Function} callback
 * @return {Array}
 * @private
 */
function _map (array, callback) {
  // figure out what number of arguments the callback function expects
  const args = maxArgumentCount(callback)

  const recurse = function (value, index) {
    if (Array.isArray(value)) {
      return value.map(function (child, i) {
        // we create a copy of the index array and append the new index value
        return recurse(child, index.concat(i))
      })
    } else {
      // invoke the callback function with the right number of arguments
      if (args === 1) {
        return callback(value)
      } else if (args === 2) {
        return callback(value, index)
      } else { // 3 or -1
        return callback(value, index, array)
      }
    }
  }

  return recurse(array, [])
}

exports.name = 'map'
exports.factory = factory