@ysfe/array-groupby/src/lib/group-by.ts

array group by function. support Array.prototype

/**
 * 数组分组函数(根据指定条件分组) array grouy by .
 * @description array extand function
 * @version 1.0.1 下个版本实现将方法写入Array.prototype,并直接在数组中使用.
 * @param array origin array
 * @param compute diff a and b ,return whether to be divided into a group
 * @param isSorted if origin array is sorted,then you can input isSorted is true. this speeds up grouping,but there are risks in this operation.
 *
 */
export const GroupBy = <T>(array: Array<T>, compute: (a: T, b: T) => boolean, isSorted?: boolean): Array<Array<T>> => {
    let r = new Array<Array<T>>(0)
    let db = (r: Array<Array<T>>, n: T, compute: (a: T, b: T) => boolean, index: number = 0): number => {
        if (r[index] && compute(n, r[index][0])) return index
        else if (r.length > index) return db(r, n, compute, index + 1)
        else return -1
    }
    // diff and merge to result
    for (let n = 0, lastIndex = 0, index = 0, a = null; n < array.length; n++) {
        a = array[n]
        if (r.length == 0) {
            r.push([a])
        } else {
            // # 优化: if origin array is sorted,
            index = db(r, a, compute, isSorted ? lastIndex : 0)
            if (index === -1) {
                r.push([a])
                lastIndex = 0
            } else {
                r[index].push(a)
                lastIndex = index
            }
        }
    }
    return r
}