mathjs/lib/utils/collection/reduce.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';

var arraySize = require('../array').size;

var isMatrix = require('../collection/isMatrix');

var IndexError = require('../../error/IndexError');
/**
 * Reduce a given matrix or array to a new matrix or
 * array with one less dimension, applying the given
 * callback in the selected dimension.
 * @param {Array | Matrix} mat
 * @param {number} dim
 * @param {Function} callback
 * @return {Array | Matrix} res
 */


module.exports = function (mat, dim, callback) {
  var size = Array.isArray(mat) ? arraySize(mat) : mat.size();

  if (dim < 0 || dim >= size.length) {
    // TODO: would be more clear when throwing a DimensionError here
    throw new IndexError(dim, size.length);
  }

  if (isMatrix(mat)) {
    return mat.create(_reduce(mat.valueOf(), dim, callback));
  } else {
    return _reduce(mat, dim, callback);
  }
};
/**
 * Recursively reduce a matrix
 * @param {Array} mat
 * @param {number} dim
 * @param {Function} callback
 * @returns {Array} ret
 * @private
 */


function _reduce(mat, dim, callback) {
  var i, ret, val, tran;

  if (dim <= 0) {
    if (!Array.isArray(mat[0])) {
      val = mat[0];

      for (i = 1; i < mat.length; i++) {
        val = callback(val, mat[i]);
      }

      return val;
    } else {
      tran = _switch(mat);
      ret = [];

      for (i = 0; i < tran.length; i++) {
        ret[i] = _reduce(tran[i], dim - 1, callback);
      }

      return ret;
    }
  } else {
    ret = [];

    for (i = 0; i < mat.length; i++) {
      ret[i] = _reduce(mat[i], dim - 1, callback);
    }

    return ret;
  }
}
/**
 * Transpose a matrix
 * @param {Array} mat
 * @returns {Array} ret
 * @private
 */


function _switch(mat) {
  var I = mat.length;
  var J = mat[0].length;
  var i, j;
  var ret = [];

  for (j = 0; j < J; j++) {
    var tmp = [];

    for (i = 0; i < I; i++) {
      tmp.push(mat[i][j]);
    }

    ret.push(tmp);
  }

  return ret;
}