bucketing/lib/index.js

group an array of items into buckets

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
/**
 * Takes `items`, buckets them using the labels generated from the `by`
 * function, and keys those labels using the keys generated from the `on`
 * function. The `on` function must generate unique keys for a given label:
 * no two labels should share the same key.
 *
 * @param items The list of items to group
 * @param by A function that produces a label given an item
 * @param on A function that produces a key given a label
 */
function group(items, by, on) {
    var labels = [];
    var keyToItems = {};
    var keyToLabel = {};
    for (var _i = 0, items_1 = items; _i < items_1.length; _i++) {
        var item = items_1[_i];
        var label = by(item);
        var key = on(label);
        if (!(key in keyToLabel)) {
            keyToLabel[key] = label;
            labels.push(label);
        }
        if (!(key in keyToItems)) {
            keyToItems[key] = [];
        }
        keyToItems[key].push(item);
    }
    return { items: items, labels: labels, keyToItems: keyToItems, keyToLabel: keyToLabel };
}
exports.group = group;