值 未在 Angular 中的键值对中输入

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，除了每个类别的所有项目都没有进入新对象newcat。

控制台上的结果应该是这样的.log：

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

相反，它像这样来：

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

我不知道为什么所有元素都没有进入

Answer 1

如果您已经在使用 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循环而不是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：

您的实现有两个问题。首先，设置isPresent的for/in循环在找到匹配项后不会break。其次，末尾的else语句会导致不推送类别中的第一项，因为您所做的只是创建空的类别数组。这是修复：

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 = {};
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
break;
}
else {
isPresent= false
}
}
if(isPresent== false){
newcat[cat] = []
}
newcat[cat].push(records[i])
}
console.log(newcat);

Answer 2

如果你使用ecmascript-6 作为标记，你应该可以访问 spread 运算符，而不必使用 Lodash 的繁重：

这基本上应该为您完成所有工作：

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

工作片段如下：

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)