| 1 | /**
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| 2 | * Implementation of Combinations
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| 3 | * Combinations are unique subsets of a collection - in this case, k x from a collection at a time.
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| 4 | * https://en.wikipedia.org/wiki/Combination
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| 5 | * @param {Array} x any type of data
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| 6 | * @param {int} k the number of objects in each group (without replacement)
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| 7 | * @returns {Array<Array>} array of permutations
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| 8 | * @example
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| 9 | * combinations([1, 2, 3], 2); // => [[1,2], [1,3], [2,3]]
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| 10 | */
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| 11 |
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| 12 | function combinations(x, k) {
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| 13 | let i;
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| 14 | let subI;
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| 15 | const combinationList = [];
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| 16 | let subsetCombinations;
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| 17 | let next;
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| 18 |
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| 19 | for (i = 0; i < x.length; i++) {
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| 20 | if (k === 1) {
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| 21 | combinationList.push([x[i]]);
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| 22 | } else {
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| 23 | subsetCombinations = combinations(x.slice(i + 1, x.length), k - 1);
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| 24 | for (subI = 0; subI < subsetCombinations.length; subI++) {
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| 25 | next = subsetCombinations[subI];
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| 26 | next.unshift(x[i]);
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| 27 | combinationList.push(next);
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| 28 | }
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| 29 | }
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| 30 | }
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| 31 | return combinationList;
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| 32 | }
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| 33 |
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| 34 | export default combinations;
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