Reduce应用 （持续更新中）

• 一、去重；

function deduplicate(arr, key)?{
  return arr.reduce((acc, cur) =>?{
    const target = key???cur[key]?: cur;
    if (!acc.has(target))?{
      acc.set(target, cur);
????}
    return acc;
??}, new Map()).values();
}

二、求和；

function?sum(arr,key)?{
????return?arr.reduce((acc,?curr)?=>?acc?+?`${key???curr[key]?:?curr}`,?0);??
}

三、拍平；

function flatten(arr, depth = 1)?{
  return arr.reduce((acc, val) =>?{
    return acc.concat(depth > 1 && Array.isArray(val)???flatten(val, depth - 1) : val);
??},?[]);
}
const arr =?[[1, 2],?[3, 4],?[5, 6]]；
const result = flatten(arr, len);
console.log(result); //?[1, 2, 3, 4, 5, 6];

四、升维；

function chunkArray(arr, len = 2)?{
  return arr.reduce((acc, curr, index) =>?{
    const chunkIndex = Math.floor(index / len);
    if (!acc[chunkIndex])?{
      acc[chunkIndex]?=?[];
????}
    acc[chunkIndex].push(curr);
    return acc;
??},?[]);
}
const arr =?[1, 2, 3, 4, 5, 6];
const result = chunkArray(arr, len);
console.log(result); //?[[1, 2],?[3, 4],?[5, 6]]

五、按条件分组

const groupBy = (arr, key) =>?{
  return arr.reduce((acc, curr) =>?{
    const key = curr =>?{?return curr[key]};
    if (!acc[key])?{
      acc[key]?=?[];
????}
    acc[key].push(curr);
    return acc;
??},?{});
};