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copied!<p>I think this should work:</p> <pre><code>var a = [1, 3, 5, 9]; var l = a.length; var r = []; for (var i = 0; i < l; ++i) { for (var j = i + 1; j < l; ++j) { for (var k = j + 1; k < l; ++k) { r.push(a[i] * a[j] * a[k]); } } } </code></pre> <p><strong>Edit</strong></p> <p>Just for my own edification, I figured out a generic solution that uses loops instead of recursion. It's obvious downside is that it's longer thus slower to load or to read. On the other hand (at least on Firefox on my machine) it runs about twice as fast as the recursive version. However, I'd only recommend it if you're finding combinations for large sets, or finding combinations many times on the same page. Anyway, in case anybody's interested, here's what I came up with.</p> <pre><code>function combos(superset, size) { var result = []; if (superset.length < size) {return result;} var done = false; var current_combo, distance_back, new_last_index; var indexes = []; var indexes_last = size - 1; var superset_last = superset.length - 1; // initialize indexes to start with leftmost combo for (var i = 0; i < size; ++i) { indexes[i] = i; } while (!done) { current_combo = []; for (i = 0; i < size; ++i) { current_combo.push(superset[indexes[i]]); } result.push(current_combo); if (indexes[indexes_last] == superset_last) { done = true; for (i = indexes_last - 1; i > -1 ; --i) { distance_back = indexes_last - i; new_last_index = indexes[indexes_last - distance_back] + distance_back + 1; if (new_last_index <= superset_last) { indexes[indexes_last] = new_last_index; done = false; break; } } if (!done) { ++indexes[indexes_last - distance_back]; --distance_back; for (; distance_back; --distance_back) { indexes[indexes_last - distance_back] = indexes[indexes_last - distance_back - 1] + 1; } } } else {++indexes[indexes_last]} } return result; } function products(sets) { var result = []; var len = sets.length; var product; for (var i = 0; i < len; ++i) { product = 1; inner_len = sets[i].length; for (var j = 0; j < inner_len; ++j) { product *= sets[i][j]; } result.push(product); } return result; } console.log(products(combos([1, 3, 5, 7, 9, 11], 3))); </code></pre>

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