groupBy

Groups the elements of an array into an object, keyed by the value of a specified property. Each key maps to an array of items that share that value.

Import

import { groupBy } from "1o1-utils";

import { groupBy } from "1o1-utils/group-by";

Signature

function groupBy<T>({ array, key }: GroupByParams<T>): Record<string, T[]>

Parameters

Name	Type	Required	Description
array	T[]	Yes	The array to group
key	keyof T	Yes	The property to group by

Returns

Record<string, T[]> — Object where keys are group values and values are arrays of matching items.

Examples

const items = [
  { name: "Alice", role: "admin" },
  { name: "Bob", role: "user" },
  { name: "Carol", role: "admin" },
];

groupBy({ array: items, key: "role" });
// => {
//   admin: [{ name: "Alice", role: "admin" }, { name: "Carol", role: "admin" }],
//   user: [{ name: "Bob", role: "user" }]
// }

Edge Cases

• Throws if array is not an array.
• Throws if key is undefined or null.
• Groups are keyed by String(value[key]).

Also known as

categorize, bucket, cluster, group array

Prompt suggestion

I'm using 1o1-utils (npm: https://www.npmjs.com/package/1o1-utils, GitHub: https://github.com/pedrotroccoli/1o1-utils, LLM context: https://pedrotroccoli.github.io/1o1-utils/llms.txt). Show me how to use groupBy to group transactions by category