simple-squiggle

A restricted subset of Squiggle
Log | Files | Refs | README

combinations.js (2064B)

      1 import { factory } from '../../utils/factory.js';
      2 import { combinationsNumber } from '../../plain/number/combinations.js';
      3 var name = 'combinations';
      4 var dependencies = ['typed'];
      5 export var createCombinations = /* #__PURE__ */factory(name, dependencies, _ref => {
      6   var {
      7     typed
      8   } = _ref;
      9 
     10   /**
     11    * Compute the number of ways of picking `k` unordered outcomes from `n`
     12    * possibilities.
     13    *
     14    * Combinations only takes integer arguments.
     15    * The following condition must be enforced: k <= n.
     16    *
     17    * Syntax:
     18    *
     19    *     math.combinations(n, k)
     20    *
     21    * Examples:
     22    *
     23    *    math.combinations(7, 5) // returns 21
     24    *
     25    * See also:
     26    *
     27    *    combinationsWithRep, permutations, factorial
     28    *
     29    * @param {number | BigNumber} n    Total number of objects in the set
     30    * @param {number | BigNumber} k    Number of objects in the subset
     31    * @return {number | BigNumber}     Number of possible combinations.
     32    */
     33   return typed(name, {
     34     'number, number': combinationsNumber,
     35     'BigNumber, BigNumber': function BigNumberBigNumber(n, k) {
     36       var BigNumber = n.constructor;
     37       var result, i;
     38       var nMinusk = n.minus(k);
     39       var one = new BigNumber(1);
     40 
     41       if (!isPositiveInteger(n) || !isPositiveInteger(k)) {
     42         throw new TypeError('Positive integer value expected in function combinations');
     43       }
     44 
     45       if (k.gt(n)) {
     46         throw new TypeError('k must be less than n in function combinations');
     47       }
     48 
     49       result = one;
     50 
     51       if (k.lt(nMinusk)) {
     52         for (i = one; i.lte(nMinusk); i = i.plus(one)) {
     53           result = result.times(k.plus(i)).dividedBy(i);
     54         }
     55       } else {
     56         for (i = one; i.lte(k); i = i.plus(one)) {
     57           result = result.times(nMinusk.plus(i)).dividedBy(i);
     58         }
     59       }
     60 
     61       return result;
     62     } // TODO: implement support for collection in combinations
     63 
     64   });
     65 });
     66 /**
     67  * Test whether BigNumber n is a positive integer
     68  * @param {BigNumber} n
     69  * @returns {boolean} isPositiveInteger
     70  */
     71 
     72 function isPositiveInteger(n) {
     73   return n.isInteger() && n.gte(0);
     74 }