differenceBy

Returns values whose derived keys do not occur in the comparison arrays.

Code

differenceBy.ts

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

/** Returns values whose derived keys are absent from every other array. */
export const differenceBy = <const Source, Key, const Comparison = Source>(
  array: readonly Source[],
  others: ReadonlyArray<readonly Comparison[]>,
  getKey: DifferenceBySelector<Source, Comparison, Key>,
): Source[] => {
  const excluded = new 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");
    }
    for (let index = 0; index < other.length; index += 1) {
      if (!Object.hasOwn(other, index)) continue;
      excluded.add(getKey(other[index] as Comparison, index, other));
    }
  }
  const result: Source[] = [];
  for (let index = 0; index < array.length; index += 1) {
    if (!Object.hasOwn(array, index)) continue;
    const value = array[index] as Source;
    if (!excluded.has(getKey(value, index, array))) result.push(value);
  }
  return result;
};

Download

wget

Terminal

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

degit

Terminal

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

Examples

differenceBy.example.ts

import { differenceBy } from "./differenceBy";

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

Props

• array (readonly Source[]) — Values to filter. Empty slots are skipped.
• others (readonly (readonly Comparison[])[]) — Arrays containing excluded keys. Empty slots in the list or its arrays are skipped.
• getKey ((value: Source | Comparison, index, array: readonly (Source | Comparison | undefined)[]) => Key) — Produces the comparison key 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.