stress: utils like lodash / understore

src/stress/groupBy.spec.ts

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+import { groupBy } from './groupBy';
+
+describe(groupBy, () => {
+  it('groups value with provided keyer()', () => {
+    expect(groupBy([], () => 0)).toEqual({});
+    expect(groupBy(new Set([1, 2, 4]), (v) => v % 2)).toEqual({
+      1: [1],
+      0: [2, 4],
+    });
+  });
+});

src/stress/groupBy.ts

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+import { DefaultMap } from '../collection/default-map';
+
+export function groupBy<T, K extends string | number | symbol>(
+  values: Iterable<T>,
+  keyer: (value: T) => K,
+): Record<K, T[]> {
+  return Object.fromEntries(groupByAsMap(values, keyer)) as Record<K, T[]>;
+}
+
+export function groupByAsMap<T, K>(values: Iterable<T>, keyer: (value: T) => K): ReadonlyMap<K, T[]> {
+  const map = new DefaultMap<K, T[]>(() => []);
+  for (const v of values) {
+    map.getOrCreate(keyer(v)).push(v);
+  }
+  return map;
+}

src/stress/orderBy.spec.ts

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+import { orderBy } from './orderBy';
+
+describe('orderBy', function () {
+  it('sorts value DESC by "natural" JS ordering', () => {
+    expect(orderBy([2, 3, 1], (v) => v)).toEqual([3, 2, 1]);
+    expect(orderBy([1, 1, 2], (v) => v)).toEqual([2, 1, 1]);
+  });
+  it('sorts value ASC by "natural" JS ordering', () => {
+    expect(orderBy([2, 3, 1], (v) => v, true)).toEqual([1, 2, 3]);
+    expect(orderBy([1, 1, 2], (v) => v, true)).toEqual([1, 1, 2]);
+  });
+});

src/stress/orderBy.ts

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+/**
+ * (for more complicated case, consider fp-ts Order<T> typeclass)
+ * @param values
+ * @param key
+ * @param asc
+ */
+export function orderBy<T, O>(values: T[], key: (v: T) => O, asc = false): T[] {
+  const indexes = values.map((v, i) => ({ v, i }));
+  return indexes.sort((a, b) => (asc ? compare(a.v, b.v) : -compare(a.v, b.v))).map((_) => _.v);
+}
+
+function compare(a: any, b: any): number {
+  if (a < b) {
+    return -1;
+  } else if (a > b) {
+    return 1;
+  } else return 0;
+}