从 JSON 中 Select 不同的值

发布于07月22日

I have my JSON as follows

{"DATA": [{"id":11,"name":"ajax","subject":"OR","mark":63},
{"id":12,"name":"javascript","subject":"OR","mark":63},
{"id":13,"name":"jquery","subject":"OR","mark":63},
{"id":14,"name":"ajax","subject":"OR","mark":63},
{"id":15,"name":"jquery","subject":"OR","mark":63},
{"id":16,"name":"ajax","subject":"OR","mark":63},
{"id":20,"name":"ajax","subject":"OR","mark":63}],"COUNT":"120"}

有什么好方法可以从这个JSON中找出distinct name吗

Result javascript,jquery,ajax

我可以用下面的方法

var arr=[''];
var j=0;
for (var i = 0; i < varjson.DATA.length; i++) {
  if($.inArray(varjson.DATA[i]["name"],arr)<0){
      arr[j]=varjson.DATA[i]["name"];
      j++;
  }
}

有没有better method个能给我更好的表现？

推荐答案

如果您想节省一些周期，我会使用一个对象和一个数组:

var lookup = {};
var items = json.DATA;
var result = [];

for (var item, i = 0; item = items[i++];) {
  var name = item.name;

  if (!(name in lookup)) {
    lookup[name] = 1;
    result.push(name);
  }
}

In this way you're basically avoiding the indexOf / inArray call, and you will get an Array that can be iterate quicker than iterating object's properties – also because in the second case you need to check hasOwnProperty.

Of course if you're fine with just an Object you can avoid the check and the result.push at all, and in case get the array using Object.keys(lookup), but it won't be faster than that.