javascript - 查找具有多次匹配属性的 JSON 对象

Question

我需要在 json 数组中找到具有相同名称属性的每个元素，例如这里的 Alaska 是两次，然后我需要比较两个对象的 lastupdate 并选择具有最新更新时间的那个。采用 stackoverflow 中的答案(抱歉，我丢失了链接)我可以删除具有相同名称属性的对象，但如何保留具有最新更新时间的对象？

[{
    "name": "Alaska",
    "Republican_fre": 3,
    "Democrats_fre": 0,
    "winner": "R",
    "iso_2": "AK",
    "electoral_vote": 3,
    "totalComponents": 3,
    "date": "29.06.2016",
    "lastupdate": "1467233426"
}, {
    "name": "Alabama",
    "Republican_fre": 3,
    "Democrats_fre": 0,
    "winner": "R",
    "iso_2": "AL",
    "electoral_vote": 9,
    "totalComponents": 3,
    "date": "29.06.2016",
    "lastupdate": "1467233426"
}, {
    "name": "Arkansas",
    "Republican_fre": 2,
    "Democrats_fre": 0,
    "winner": "R",
    "iso_2": "AR",
    "electoral_vote": 6,
    "totalComponents": 2,
    "date": "29.06.2016",
    "lastupdate": "1467233426"
},
{
    "name": "Alaska",
    "Republican_fre": 5,
    "Democrats_fre": 0,
    "winner": "R",
    "iso_2": "AK",
    "electoral_vote": 3,
    "totalComponents": 5,
    "date": "29.06.2016",
    "lastupdate": "1467282133"                 
}]

代码:

function arrUnique(arr) {
    var cleaned = [];
    data.forEach(function(itm) {
        var unique = true;
        cleaned.forEach(function(itm2) {
         var minValue = Math.min(itm.lastupdate, itm2.lastupdate)
            if (_.isEqual(itm.name, itm2.name)){
            unique = false;
            } 
        });
        if (unique)  cleaned.push(itm);
    });
    return cleaned;
}

var uniqueStandards = arrUnique(data);

jsfiddle:

预期输出预期的输出是它保留具有最新“lastupdate”值的 Alsaka 对象之一。所以它首先检查具有相同名称属性的对象，然后比较上次更新值并保留具有最新值的对象

Answer 1

您可以使用下划线的 sortBy()按 lastupdate 键对集合中的项目进行排序，reverse()让所有项目按 lastupdate 降序排列，然后使用 uniq()仅保留唯一的 name 项。

var uniqueStandards = _.uniq(_.sortBy(data, 'lastupdate').reverse(), 'name');

var data = [{
  "name": "Alaska",
  "Republican_fre": 3,
  "Democrats_fre": 0,
  "winner": "R",
  "iso_2": "AK",
  "electoral_vote": 3,
  "totalComponents": 3,
  "date": "29.06.2016",
  "lastupdate": "1467233426"
}, {
  "name": "Alabama",
  "Republican_fre": 3,
  "Democrats_fre": 0,
  "winner": "R",
  "iso_2": "AL",
  "electoral_vote": 9,
  "totalComponents": 3,
  "date": "29.06.2016",
  "lastupdate": "1467233426"
}, {
  "name": "Arkansas",
  "Republican_fre": 2,
  "Democrats_fre": 0,
  "winner": "R",
  "iso_2": "AR",
  "electoral_vote": 6,
  "totalComponents": 2,
  "date": "29.06.2016",
  "lastupdate": "1467233426"
}, {
  "name": "Alaska",
  "Republican_fre": 5,
  "Democrats_fre": 0,
  "winner": "R",
  "iso_2": "AK",
  "electoral_vote": 3,
  "totalComponents": 5,
  "date": "29.06.2016",
  "lastupdate": "1467282133"
}];

var uniqueStandards = _.uniq(_.sortBy(data, 'lastupdate').reverse(), 'name');

document.body.innerHTML = '<pre>' + JSON.stringify(uniqueStandards, 0, 4) + '</pre>';

<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js"></script>

---

普通的 JS 解决方案是:

var uniqueStandards = data
.slice() // this makes sure that we're not mutating the original array
.sort(function(x, y) { return y.lastupdate - x.lastupdate; }) // sort in descending order
.filter(function(x) {  // this ensure items with unique names
  return (this[x.name]? false: (this[x.name] = true));
}, {});

var data = [{
  "name": "Alaska",
  "Republican_fre": 3,
  "Democrats_fre": 0,
  "winner": "R",
  "iso_2": "AK",
  "electoral_vote": 3,
  "totalComponents": 3,
  "date": "29.06.2016",
  "lastupdate": "1467233426"
}, {
  "name": "Alabama",
  "Republican_fre": 3,
  "Democrats_fre": 0,
  "winner": "R",
  "iso_2": "AL",
  "electoral_vote": 9,
  "totalComponents": 3,
  "date": "29.06.2016",
  "lastupdate": "1467233426"
}, {
  "name": "Arkansas",
  "Republican_fre": 2,
  "Democrats_fre": 0,
  "winner": "R",
  "iso_2": "AR",
  "electoral_vote": 6,
  "totalComponents": 2,
  "date": "29.06.2016",
  "lastupdate": "1467233426"
}, {
  "name": "Alaska",
  "Republican_fre": 5,
  "Democrats_fre": 0,
  "winner": "R",
  "iso_2": "AK",
  "electoral_vote": 3,
  "totalComponents": 5,
  "date": "29.06.2016",
  "lastupdate": "1467282133"
}];

var uniqueStandards = data
.slice() // this makes sure that we're not mutating the original array
.sort(function(x, y) { return y.lastupdate - x.lastupdate; }) // sort in descending order
.filter(function(x) {  // this ensure items with unique names
  return (this[x.name]? false: (this[x.name] = true));
}, {});

document.body.innerHTML = '<pre>' + JSON.stringify(uniqueStandards, 0, 4) + '</pre>';

---

或者，您可以提供 lodash尝试一下:

var uniqueStandards = _(data).orderBy('lastupdate', 'desc').uniqBy('name').value();

上面的代码片段使用了 orderBy()按 lastupdate 降序排列集合，uniqBy()以确保该集合仅具有唯一名称。

var data = [{
  "name": "Alaska",
  "Republican_fre": 3,
  "Democrats_fre": 0,
  "winner": "R",
  "iso_2": "AK",
  "electoral_vote": 3,
  "totalComponents": 3,
  "date": "29.06.2016",
  "lastupdate": "1467233426"
}, {
  "name": "Alabama",
  "Republican_fre": 3,
  "Democrats_fre": 0,
  "winner": "R",
  "iso_2": "AL",
  "electoral_vote": 9,
  "totalComponents": 3,
  "date": "29.06.2016",
  "lastupdate": "1467233426"
}, {
  "name": "Arkansas",
  "Republican_fre": 2,
  "Democrats_fre": 0,
  "winner": "R",
  "iso_2": "AR",
  "electoral_vote": 6,
  "totalComponents": 2,
  "date": "29.06.2016",
  "lastupdate": "1467233426"
}, {
  "name": "Alaska",
  "Republican_fre": 5,
  "Democrats_fre": 0,
  "winner": "R",
  "iso_2": "AK",
  "electoral_vote": 3,
  "totalComponents": 5,
  "date": "29.06.2016",
  "lastupdate": "1467282133"
}];

var uniqueStandards = _(data).orderBy('lastupdate', 'desc').uniqBy('name').value();

document.body.innerHTML = '<pre>' + JSON.stringify(uniqueStandards, 0, 4) + '</pre>';

<script src="https://cdn.jsdelivr.net/lodash/4.13.1/lodash.min.js"></script>