tamda/dist/list/partition.js

Practical functional programming library for TypeScript

import { identity } from '../function/identity';
import { infer } from '../function/infer';
export function partition() {
    return inferred.apply(undefined, arguments);
}
const inferred = infer((array, keyFn = identity) => Array.from(array.reduce((map, item, index) => {
    const key = keyFn(item, index, array);
    // Initializes the array if undefined for the key.
    if (!map.get(key)) {
        map.set(key, []);
    }
    // Faster than spreading the array,safe here.
    // i.e. map.set(key, [ ...map.get(key), item ]),
    map.get(key).push(item);
    return map;
}, new Map())), args => args[0] instanceof Array);
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