aureooms-js-array/lib/map/combinations.js

array manipulation code bricks for JavaScript

'use strict';

Object.defineProperty(exports, "__esModule", {
	value: true
});
exports.combinations = combinations;

var _ = require('..');

function combinations(iterable, repeat, out) {

	// combinations('ABCD', 2) --> AB AC AD BC BD CD
	// combinations(range(4), 3) --> 012 013 023 123

	var pool, len, indices, i, j;

	pool = iterable;
	len = pool.length;

	if (repeat > len) {
		return out;
	}

	indices = (0, _.range)(0, repeat, 1, []);

	out.push((0, _.pick)(pool, indices, []));

	if (repeat === 0 || len === 0) {
		return out;
	}

	for (;;) {

		for (i = repeat - 1; i >= 0; --i) {
			if (indices[i] !== i + len - repeat) {
				break;
			}
		}

		if (i < 0) {
			return out;
		}

		++indices[i];

		for (j = i + 1; j < repeat; ++j) {
			indices[j] = indices[j - 1] + 1;
		}

		out.push((0, _.pick)(pool, indices, []));
	}
}
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