按 Javascript 对象键 + 数组分组答案

【问题标题】：Group by Javascript Object keys + array按 Javascript 对象键 + 数组分组
【发布时间】：2017-01-09 18:27:26
【问题描述】：

我正在尝试使用下划线将我的对象数组分组到一个较小的列表中：

    var list = [
  { Region: 'A', Vals: [ 7, 'H' ] },
  { Region: 'B', Vals: [ 40, 'H' ] },
  { Region: 'B', Vals: [ 24, 'VH' ] },
  { Region: 'C', Vals: [ 4, 'VH' ] },
  { Region: 'A',Vals: [ 40, 'VH' ] }
  ];


    var groups = _.groupBy(list, function(value){
        return value.Region;
    });

var grouped = _.map(groups, function(group){
        return {
            Region: group[0].Region,
            Vals: group[0].Vals
        }
    });

这会有点接近，但它缺少一些 Vals。我想要基于键连接的“vals”数组。

   var list = [
  { Region: 'A', Vals: [ 7, 'H', 40, 'VH' ] },
  { Region: 'B', Vals: [ 40, 'H',  24, 'VH' ] },
  { Region: 'B', Vals: [ 24, 'VH' ] },
  { Region: 'C', Vals: [ 4, 'VH' ] }
  ];

http://jsfiddle.net/77gL11c9/1/

【问题讨论】：

您可以通过将group[0].Vals 替换为_.flatten(_.pluck(group, 'Vals')) 来获得所有Vals
var res = list.reduce(function(arr, v) { if (!(v.Region in ref)) { ref[v.Region] = arr.length; arr.push({Region: v.Region, Vals: v.Vals}); } else{ [].push.apply(arr[ref[v.Region]].Vals, v.Vals); } return arr; }, []);

标签： javascript arrays underscore.js

【解决方案1】：

list.reduce(function (memo, v) {
  if (memo[v.Region]) {
    memo[v.Region] = memo[v.Region].concat(v.Vals)
  } else {
    memo[v.Region] = v.Vals.slice()
  }
  return memo
}, {})

输出将如下所示：

{
  A: [ 7, "H", 40, "VH" ],
  B: [40, "H", 24, "VH" ],
  C: [ 4, "VH" ]
}

【讨论】：

【解决方案2】：

使用原生 JavaScript Array#reduce 方法和引用对象来保存索引。

var list = [
  { Region: 'A', Vals: [ 7, 'H' ] },
  { Region: 'B', Vals: [ 40, 'H' ] },
  { Region: 'B', Vals: [ 24, 'VH' ] },
  { Region: 'C', Vals: [ 4, 'VH' ] },
  { Region: 'A',Vals: [ 40, 'VH' ] }
];


// object for refering index
var ref = {};

// iterate over the array
var res = list.reduce(function(arr, v) {
      // check property defined if not define and push
      // value to array
      if (!(v.Region in ref)) {
        ref[v.Region] = arr.length;
        arr.push({Region: v.Region, Vals: v.Vals});
      // if index already defined then push values
      } else{
        [].push.apply(arr[ref[v.Region]].Vals, v.Vals);
      }
    // return the array reference
    return arr;
  // set initial value as empty array
}, []);

console.log(res);

更新：如果你想生成一个对象，其中Region 值作为属性名称，Vals 值作为它的值，然后执行类似的操作。

var list = [
  { Region: 'A', Vals: [ 7, 'H' ] },
  { Region: 'B', Vals: [ 40, 'H' ] },
  { Region: 'B', Vals: [ 24, 'VH' ] },
  { Region: 'C', Vals: [ 4, 'VH' ] },
  { Region: 'A',Vals: [ 40, 'VH' ] }
];


// iterate over the array
var res = list.reduce(function(obj, v) {
  // define the property as an array if not 
  // already defined
  obj[v.Region] = obj[v.Region] || [];
  
  // push all values to array
  [].push.apply(obj[v.Region], v.Vals);
  
  // return the object reference
  return obj;
  
  // set initial value as an empty object
}, {});

console.log(res);

【讨论】：

【解决方案3】：

这将产生您正在寻找的确切输出。

//first build an object with Region properties, and add the Vals to each of those properties

var tempList = {}; 
for (var i=0; i < list.length; i++) {
  if (!(list[i].Region in tempList)) {
    tempList[list[i].Region] = [];
  }
  Array.prototype.push.apply(tempList[list[i].Region],list[i].Vals);
}

//then format this as an array of objects    
var groupedList = [];
for (var region in tempList) {
    groupedList.push({Region:region, Vals: tempList[region]});
}

list = groupedList;

在上面的代码之后，以下将是正确的：

list = [
  { Region: 'A', Vals: [ 7, 'H', 40, 'VH' ] },
  { Region: 'B', Vals: [ 40, 'H',  24, 'VH' ] },
  { Region: 'B', Vals: [ 24, 'VH' ] },
  { Region: 'C', Vals: [ 4, 'VH' ] }
];

【讨论】：