intersectionBy

Returns the first value for each derived key shared by all arrays.

Code

intersectionBy.ts

export type IntersectionBySelector<Source, Comparison, Key> = (
  this: void,
  value: Source | Comparison,
  index: number,
  array: readonly (Source | Comparison | undefined)[],
) => Key;

/** Returns the first distinct value for each derived key shared by all arrays. */
export const intersectionBy = <const Source, Key, const Comparison = Source>(
  array: readonly Source[],
  others: ReadonlyArray<readonly Comparison[]>,
  getKey: IntersectionBySelector<Source, Comparison, Key>,
): Source[] => {
  const sets: Array<Set<Key>> = [];
  for (let otherIndex = 0; otherIndex < others.length; otherIndex += 1) {
    if (!Object.hasOwn(others, otherIndex)) continue;
    const other = others[otherIndex];
    if (!Array.isArray(other)) {
      throw new TypeError("others must contain only arrays");
    }
    const keys = new Set<Key>();
    for (let index = 0; index < other.length; index += 1) {
      if (!Object.hasOwn(other, index)) continue;
      keys.add(getKey(other[index] as Comparison, index, other));
    }
    sets.push(keys);
  }
  const seen = new Set<Key>();
  const result: Source[] = [];

  for (let index = 0; index < array.length; index += 1) {
    if (!Object.hasOwn(array, index)) continue;
    const value = array[index] as Source;
    const key = getKey(value, index, array);
    if (seen.has(key) || !sets.every((set) => set.has(key))) continue;
    seen.add(key);
    result.push(value);
  }
  return result;
};

Download

wget

Terminal

wget -O src/lib/intersectionBy.ts https://raw.githubusercontent.com/jrTilak/lazykit/HEAD/registry/functions/intersectionBy.ts

degit

Terminal

temp_dir="$(mktemp -d)" && bunx degit jrTilak/lazykit/registry/functions "$temp_dir" && mv "$temp_dir/intersectionBy.ts" src/lib/intersectionBy.ts && rm -r "$temp_dir"

Examples

intersectionBy.example.ts

import { intersectionBy } from "./intersectionBy";

const shared = intersectionBy(
  [{ id: 1 }, { id: 2 }],
  [[{ id: 2 }]],
  (item) => item.id
);

Props

• array (readonly Source[]) — The ordered source array. Empty slots are skipped.
• others (readonly (readonly Comparison[])[]) — Arrays that must contain the key. Empty slots in the list or its arrays are skipped.
• getKey ((value: Source | Comparison, index, array: readonly (Source | Comparison | undefined)[]) => Key) — Produces comparison keys and is invoked without a receiver. value is always present; the current source or comparison array retains skipped holes, so reading one can produce undefined.

Returns Source[]; comparison values do not widen the result type.