Initial Commit

utils/array.ts

@@ -0,0 +1,46 @@
+export function sumArray(arr: Array<number>): number {
+  return sumBy(arr, (a) => a);
+}
+
+export function sumBy<T>(
+  arr: Array<T>,
+  by: (array: T) => number | string
+): number {
+  return arr.reduce((sum, element) => sum + Number(by(element)), 0);
+}
+
+export function multArray(arr: Array<number>): number {
+  return multBy(arr, (a) => a);
+}
+
+export function multBy<T>(
+  arr: Array<T>,
+  by: (array: T) => number | string
+): number {
+  if (arr.length <= 0) {
+    return 0;
+  }
+  return arr.reduce((sum, element) => sum * Number(by(element)), 1);
+}
+
+export function groupBy<E, K>(
+  arr: Array<E>,
+  by: (element: E) => K
+): { key: K; elements: Array<E> }[] {
+  return arr.reduce(
+    (groups, element) => {
+      const key = by(element);
+      const index = groups.findIndex((e) => e.key === key);
+
+      if (index < 0) {
+        groups.push({ key, elements: [element] });
+        return groups;
+      }
+      const existing = groups[index];
+      existing.elements.push(element);
+
+      return groups;
+    },
+    [] as { key: K; elements: Array<E> }[]
+  );
+}