thi-ng/umbrella

import { isIterable } from "@thi.ng/checks/is-iterable";
import type { Transducer } from "./api.js";
import { iterator1 } from "./iterator.js";
import { map } from "./map.js";

/**
 * Transducer which looks up given `key` in each input and yields
 * sequence of these values.
 *
 * @example
 * ```ts
 * import { pluck } from "@thi.ng/transducers";
 *
 * [...pluck("id", [{id: 1}, {id: 2}, {}])]
 * // [ 1, 2, undefined ]
 * ```
 *
 * @param key - property key
 */
export function pluck<A, B>(key: PropertyKey): Transducer<A, B>;
export function pluck<A, B>(
    key: PropertyKey,
    src: Iterable<A>
): IterableIterator<B>;
export function pluck<A>(key: PropertyKey, src?: Iterable<A>): any {
    return isIterable(src)
        ? iterator1(pluck(key), src)
        : map((x: any) => x[key]);
}