mathjs/lib/function/set/setIntersect.js

'use strict';

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

function factory (type, config, load, typed) {
  var equal = load(require('../relational/equal'));
  var index = load(require('../../type/matrix/MatrixIndex'));
  var matrix = load(require('../../type/matrix/DenseMatrix'));
  var size = load(require('../matrix/size'));
  var subset = load(require('../matrix/subset'));
  var compareNatural = load(require('../relational/compareNatural'));
  
  /**
   * Create the intersection of two (multi)sets.
   * Multi-dimension arrays will be converted to single-dimension arrays before the operation.
   *
   * Syntax:
   *
   *    math.setIntersect(set1, set2)
   *
   * Examples:
   *
   *    math.setIntersect([1, 2, 3, 4], [3, 4, 5, 6]);            // returns [3, 4]
   *    math.setIntersect([[1, 2], [3, 4]], [[3, 4], [5, 6]]);    // returns [3, 4]
   *
   * See also:
   *
   *    setUnion, setDifference
   *
   * @param {Array | Matrix}    a1  A (multi)set
   * @param {Array | Matrix}    a2  A (multi)set
   * @return {Array | Matrix}    The intersection of two (multi)sets
   */
  var setIntersect = typed('setIntersect', {
    'Array | Matrix, Array | Matrix': function (a1, a2) {
      if (subset(size(a1), new index(0)) === 0 || subset(size(a2), new index(0)) === 0) { // of any of them is empty, return empty
        var result = [];
      }
      else {
        var b1 = identify(flatten(Array.isArray(a1) ? a1 : a1.toArray()).sort(compareNatural));
        var b2 = identify(flatten(Array.isArray(a2) ? a2 : a2.toArray()).sort(compareNatural));
        var result = [];
        for (var i=0; i<b1.length; i++) {
          for (var j=0; j<b2.length; j++) {
              if (equal(b1[i].value, b2[j].value) && b1[i].identifier === b2[j].identifier) { // the identifier is always a decimal int
                result.push(b1[i]);
                break;
              }
          }
        }
      }
      // return an array, if both inputs were arrays
      if (Array.isArray(a1) && Array.isArray(a2)) {
        return generalize(result);
      }
      // return a matrix otherwise
      return new matrix(generalize(result));
    }
  });

  return setIntersect;
}

exports.name = 'setIntersect';
exports.factory = factory;