JavaScript之纯数组按指定特征分组、map、reduce、typeof、concat、length

数组分组，将传入的数据按指定特征进行分组 输入：数组值，函数或属性 输出：对象 key:数组所有元素经过处理后的值 value:相同key的数组元素集合

let arrFloatingPointNumber = [7.7, 5.2, 7.3], arrLength = ['one', 'two', 'weet', 'thren']; function groupBy(arr, fn) { return arr.map(item => { if (typeof fn === 'function') { return fn(item); } else { return item[fn]; } }).reduce((pre, cur, i) => { if (!pre[cur]) { pre[cur] = [arr[i]]; } else { pre[cur] = pre[cur].concat(arr[i]); } return pre; }, {}); } console.log('arrFloatingPointNumber:', groupBy(arrFloatingPointNumber, Math.floor)); // arrFloatingPointNumber: {5: Array(1), 7: Array(2)} console.log('arrLength:', groupBy(arrLength, 'length')); // arrLength: {3: Array(2), 4: Array(1), 5: Array(1)}