mathjs/lib/function/set/setMultiplicity.js

'use strict';

var flatten = require('../../utils/array').flatten;

function factory (type, config, load, typed) {
  var equal = load(require('../relational/equal'));
  var index = load(require('../../type/matrix/MatrixIndex'));
  var size = load(require('../matrix/size'));
  var subset = load(require('../matrix/subset'));
  
  /**
   * Count the multiplicity of an element in a multiset.
   * A multi-dimension array will be converted to a single-dimension array before the operation.
   *
   * Syntax:
   *
   *    math.setMultiplicity(set)
   *
   * Examples:
   *
   *    math.setMultiplicity(1, [1, 2, 2, 4]);    // returns 1
   *    math.setMultiplicity(2, [1, 2, 2, 4]);    // returns 2
   *
   * See also:
   *
   *    setDistinct, setSize
   *
   * @param {number | BigNumber | Fraction | Complex} e  An element in the multiset
   * @param {Array | Matrix}     a  A multiset
   * @return {number}            The number of how many times the multiset contains the element
   */
  var setMultiplicity = typed('setMultiplicity', {
    'number | BigNumber | Fraction | Complex, Array | Matrix': function (e, a) {
      if (subset(size(a), new index(0)) === 0) { // if empty, return 0
        return 0;
      }
      var b = flatten(Array.isArray(a) ? a : a.toArray());
      var count = 0;
      for (var i=0; i<b.length; i++) {
        if (equal(b[i], e)) {
          count++;
        }
      }
      return count;
    }
  });

  return setMultiplicity;
}

exports.name = 'setMultiplicity';
exports.factory = factory;