标签：组成 argument logs cab 代码示例 turn 示例 rate 代码
_.countBy(list, iteratee, [context])
排序一个列表组成一个组，并且返回各组中的对象的数量的计数。类似groupBy，但是不是返回列表的值，而是返回在该组中值的数目。就像EXCEL里的分类统计
var parity = _.countBy([1, 2, 3, 4, 5], function (num) { return num % 2 === 0; }); //符合条件的key为在true，不符合条件的key为false。 console.log(parity); //=> Object {false: 3, true: 2}
var parity = _.countBy([1, 2, 3, 4, 5], function(num) { return num % 2 == 0 ? ‘even‘: ‘odd‘; }); console.log(parity); //=> Object {odd: 3, even: 2}
var parity = _.countBy(‘12345‘, function (num) { console.log(this); //5 times => Object {no: 3} return num > this.no; }, {no : 3}); console.log(parity); //=> Object {false: 3, true: 2}
var parity = _.countBy(‘abc‘, function (element, index, list) { console.log(element, index, list); //=> a 0 abc //=> b 1 abc //=> c 2 abc }); console.log(parity); //=> Object {undefined: 3}
var list = [‘one‘, ‘two‘, ‘three‘, ‘four‘, ‘five‘, ‘six‘, ‘seven‘, ‘eight‘, ‘nine‘, ‘ten‘]; var grouped = _.countBy(list, ‘length‘); console.log(grouped); //=> Object {3: 4, 4: 3, 5: 3}
var list = [{x:‘a‘}, {x:‘b‘}, {x:‘a‘}]; var grouped = _.countBy(list, ‘x‘); console.log(grouped); //=> Object {a: 2, b: 1}
var list = [{x:0, y:0}, {x:0, y:1}, {x:1, y:1}]; var grouped = _.countBy(list, {x:0}); console.log(grouped); //=> Object {true: 2, false: 1}
var parity = _.countBy(‘abcab‘); console.log(parity); //=> Object {a: 2, b: 2, c: 1}
console.log(_.countBy(0)); //=> Object {} console.log(_.countBy(NaN)); //=> Object {} console.log(_.countBy(null)); //=> Object {} console.log(_.countBy(undefined)); //=> Object {} console.log(_.countBy(true)); //=> Object {} console.log(_.countBy(false)); //=> Object {}
underscorejs之_.countBy(list, iteratee, [context])
标签：组成 argument logs cab 代码示例 turn 示例 rate 代码
原文地址：http://www.cnblogs.com/rechel/p/7615199.html
