cluster should accept a callback instead of size argument

[aleclarson]

This allows cluster to be used similarly to group

import * as _ from 'radashi'

const data = [1, 2, 3]

const groups = _.group(data, n => n % 2)
// => { 0: [2], 1: [1, 3] }

const clusters = _.cluster(data, n => n % 2)
// => [[1, 3], [2]]

• Why not do Object.values(_.group(…))?
  Because that results in (number[] | undefined)[] and there's nothing we can do about that, except for a manual type assertion (which is error-prone).

Inspired by #287

[Minhir]

It totally breaks cluster semantics (BTW, I don't really like cluster naming. chunk sounds much better to me). We can introduce groupArr or some different name for it.

[aleclarson]

chunk makes sense, and Lodash uses it. 👍

I agree we should keep group in the name, but my rationale for that is different than yours: to make it easily discoverable and clearly related to group.

I don't fully understand the idea that it breaks cluster's semantics, since clustering/chunking is a form of grouping, but since we agree, there's no point in debating it. 😃