Question

我有一个json文件：

var records= 
[
    {
        "category" : "chinese",
        "name": "noodles"
    },
    {
        "category" : "chinese",
        "name": "veg"  
    },
    {
        "category" : "Indian",
        "name": "Dal"  
    },
    {
        "category" : "Indian",
        "name": "Rajma"  
    },
    {
        "category" : "chinese",
        "name": "chicken"  
    },
    {
        "category" : "continental",
        "name": "fish"
    },
    {
        "category" : "continental",
        "name": "Veg"
    },
    {
        "category" : "Indian",
        "name": "Paratha" 
    }
]

我正在尝试将此JSON转换为以下格式：

var newcat = 
{
   "chinese": [
               { "name": "noodles", "category": "chinese" },
               {"name": "veg", "category": "chinese"}, 
               {"name":"chicken", "category": "chinese"}
            ], 
   "indian":  [
               { "name": "Dal", "category": "indian" },
               {"name": "rajma", "category": "indian"}, 
               {"name":"chicken", "category": "indian" }
            ], 
  "continental": [
                 { "name": "fish", "category": "continental" },
                 { "name": "veg", "category": "continental"} 

            ] 
}

我在角度中使用的代码是：

var newcat={}
            var arr= {}
            var isPresent= false;
            var cat
            for (let i=0;i< records.length;i++) {
                cat= records[i].category
                for(let item in newcat) {
                    if(cat == item) {
                        isPresent= true
                    }
                    else {
                            isPresent= false
                    }
                }
                if(isPresent== false){
                    newcat[cat]= []
                }
                else {
                    newcat[cat].push(records[i])
                    console.log("===>",newcat)
                }

            }

我能够构建对象，除此之外，每个类别的所有项目都没有输入新对象 newcat 。

结果应该在console.log上显示：

{chinese: Array(3), indian: Array(3), continental: Array(2)}

相反它会像：

{chinese: Array(0), indian: Array(1), continental: Array(1)}

我无法弄清楚为什么所有元素都没有进入

Answer 1

如果您已经使用Lodash，请使用_.groupBy。否则，您可以编写自己的groupBy函数：

var records = [
    {
        "category" : "chinese",
        "name": "noodles"
    },
    {
        "category" : "chinese",
        "name": "veg"  
    },
    {
        "category" : "Indian",
        "name": "Dal"  
    },
    {
        "category" : "Indian",
        "name": "Rajma"  
    },
    {
        "category" : "chinese",
        "name": "chicken"  
    },
    {
        "category" : "continental",
        "name": "fish"
    },
    {
        "category" : "continental",
        "name": "Veg"
    },
    {
        "category" : "Indian",
        "name": "Paratha" 
    }
];

function groupBy(array, key) {
  return array.reduce((groups, value) => {
    const group = groups[value[key]] || (groups[value[key]] = []);
    group.push(value);
    return groups;
  }, {});
}

console.log(groupBy(records, 'category'));

或者，使用for循环代替reduce：

function groupBy(array, key) {
  const groups = {};
  for(let i = 0; i < array.length; i++) {
    const value = array[i];
    const valueKey = value[key];
    if(!groups[valueKey]) groups[valueKey] = [];
    groups[valueKey].push(value);
  }
  return groups;
}

编辑：修复现有代码：

您的实施有两个问题。首先，设置for/in的{{1}}循环在找到匹配后不会isPresent。其次，最后的break语句会导致类别中的第一项不被推送，因为您所做的就是创建空类别数组。这是修复：

else

Answer 2

如果您使用ecmascript-6作为标记，您应该可以访问传播运算符而不会使用Lodash：

这基本上应该为你完成所有工作：

records.map(item => {
    newcat[item.category.toLowerCase()] = newcat[item.category.toLowerCase()] || []
    newcat[item.category.toLowerCase()] = [
        ...newcat[item.category.toLowerCase()],
        { ...item }
    ] 
})

下面的工作代码段：

＆＃13;

var records = [{
    "category": "chinese",
    "name": "noodles"
  },
  {
    "category": "chinese",
    "name": "veg"
  },
  {
    "category": "Indian",
    "name": "Dal"
  },
  {
    "category": "Indian",
    "name": "Rajma"
  },
  {
    "category": "chinese",
    "name": "chicken"
  },
  {
    "category": "continental",
    "name": "fish"
  },
  {
    "category": "continental",
    "name": "Veg"
  },
  {
    "category": "Indian",
    "name": "Paratha"
  }
]

var newcat = {}

records.map(item => {
  newcat[item.category.toLowerCase()] = newcat[item.category.toLowerCase()] || []
  newcat[item.category.toLowerCase()] = [
    ...newcat[item.category.toLowerCase()],
    { ...item }
  ]
})

console.log(newcat)

＆＃13;

值未在Angular中输入键值对

2 个答案: