我使用underscore.js来查找数组中的所有唯一项,但我无法弄清楚如何获得返回的唯一项的数量。
_PERSONARRAY = [{name:"tom",age:7}{name:"john",age:9}{name:"becky",age:2}{name:"sam",age:7}]
_UNIQUEAGEARRAY = _.chain(_PERSONARRAY).map(function(person) { return person.age }).uniq().value();
在这种情况下,_UNIQUEAGEARRAY将等于:
[7,9,2]
我实际需要返回的是:
[{uniqueAge:7,numberOfPeople:2}{uniqueAge:9,numberOfPeople:1}{uniqueAge:2,numberOfPeople:1}]
感谢帮助。另外,我假设_underscore.js很快就这样做了?如果这是愚蠢的慢,告诉我因为我会接受其他解决方案。
我想你正在寻找countBy
功能:
_UNIQUEAGEARRAY = _.countBy(_PERSONARRAY, "age");
它产生了结果:
{"2":1,"7":2,"9":1}
JSぇdでも但是:z zxswい
一个不错的解决方案是使用可选的迭代器函数来强调http://jsfiddle.net/4J2SX/函数:
uniq
文件:let people = [
{name: "Alice", age: 21},
{name: "Bob", age: 34},
{name: "Caroline", age: 21}
];
_.uniq(people, person => person.age);
如果需要,可以使用下划线的groupBy(对于大型数据集可能不是一个好主意,因为它保留了所有分组项的列表)
例:
http://underscorejs.org/#uniq
如果要将其映射到您的确切格式,请尝试在groupBy之后执行映射:
var d = _.groupBy(_PERSONARRAY, function(p){
return p.age;
});
的jsfiddle:var x = _.map(d, function(people, age) {
return {uniqueAge: age, numberOfPeople: people.length};
});
http://jsfiddle.net/jsgkC/2/功能很有用。
groupBy
会产生输出
_personsList = [{name:"anjo",age:5},{name:"george",age:3},{name:"jack",age:5}];
_uniqAgeList = _.groupBy(_personsList, "age");
的jsfiddle:{
"3":[{"name":"george","age":3}],
"5":[{"name":"anjo","age":5},{"name":"jack","age":5}]
}