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95 lines
3.0 KiB
JavaScript
95 lines
3.0 KiB
JavaScript
// SetManipulator MIT Licence © 2016 Edwin Monk-Fromont http://github.com/edmofro
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// Based on setOps.js MIT License © 2014 James Abney http://github.com/jabney
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// Set operations union, intersection, symmetric difference,
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// relative complement, equals. Set operations are fast.
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class SetManipulator {
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constructor() {
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// Create and push the uid identity method.
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let identityExtractor = (identity) => identity;
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this.uidList = [identityExtractor];
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this.uid = identityExtractor;
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}
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// Processes a histogram consructed from two arrays, 'a' and 'b'.
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// This function is used generically by the below set operation
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// methods, a.k.a, 'evaluators', to return some subset of
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// a set union, based on frequencies in the histogram.
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process(a, b, evaluator) {
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// If identity extractor passed in, push it on the stack
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//if (identityExtractor) this.pushIdentityExtractor(identityExtractor);
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// Create a histogram of 'a'.
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const hist = {};
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const out = [];
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let ukey;
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a.forEach((value) => {
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ukey = this.uid(value);
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if (!hist[ukey]) {
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hist[ukey] = { value: value, freq: 1 };
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}
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});
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// Merge 'b' into the histogram.
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b.forEach((value) => {
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ukey = this.uid(value);
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if (hist[ukey]) {
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if (hist[ukey].freq === 1) hist[ukey].freq = 3;
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} else hist[ukey] = { value: value, freq: 2 };
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});
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// Pop any new identity extractor
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//if (identityExtractor) this.popIdentityExtractor(identityExtractor);
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// Call the given evaluator.
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if (evaluator) {
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for (const key in hist) {
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//if (!hist.hasOwnProperty(key)) continue; // Property from object prototype, skip
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if (evaluator(hist[key].freq)) out.push(hist[key].value);
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}
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return out;
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}
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return hist;
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}
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// Join two sets together.
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// Set.union([1, 2, 2], [2, 3]) => [1, 2, 3]
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union(a, b) {
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return this.process(a, b, () => true);
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}
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// Return items common to both sets.
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// Set.intersection([1, 1, 2], [2, 2, 3]) => [2]
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intersection(a, b) {
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return this.process(a, b, (freq) => freq === 3);
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}
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// Symmetric difference. Items from either set that
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// are not in both sets.
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// Set.difference([1, 1, 2], [2, 3, 3]) => [1, 3]
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difference(a, b) {
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return this.process(a, b, (freq) => freq < 3);
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}
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// Relative complement. Items from 'a' which are
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// not also in 'b'.
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// Set.complement([1, 2, 2], [2, 2, 3]) => [3]
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complement(a, b) {
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return this.process(a, b, (freq) => freq === 1);
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}
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// Returns true if both sets are equivalent, false otherwise.
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// Set.equals([1, 1, 2], [1, 2, 2]) => true
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// Set.equals([1, 1, 2], [1, 2, 3]) => false
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equals(a, b) {
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let max = 0;
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let min = Math.pow(2, 53);
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const hist = this.process(a, b);
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for (const key in hist) {
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// if (!hist.hasOwnProperty(key)) continue; // Property from object prototype, skip
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max = Math.max(max, hist[key].freq);
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min = Math.min(min, hist[key].freq);
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}
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return min === 3 && max === 3;
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}
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}
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const setManipulator = new SetManipulator();
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export default setManipulator;
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