javascript - 值未输入 Angular 中的键值对

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 Angular 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)
                }

            }

除了每个类别的所有项目都没有进入新对象 newcat 之外，我能够构建对象。

console.log 中的结果应该是这样的:

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

相反，它是这样的:

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

我不明白为什么所有的元素都没有进入

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:修复您现有的代码:

您的实现有两个问题。首先，设置isPresent 的for/in 循环在找到匹配后不会中断。其次，末尾的 else 语句导致类别中的第一项不被推送，因为您所做的只是创建空类别数组。这里有修复:

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);