从对象数组中计算特定键值

Question

我有以下JSON数组我想创建对象表单状态键计数

[
  {
    "id": "65:0",    
    "status": "ORANGE"
  },
  {
    "id": "65:0",
    "status": "GREEN"
  },
  {
    "id": "65:0",
    "status": "ORANGE"
  },
  {
    "id": "65:0",
    "status": "YELLOW"
  },
  {
    "id": "65:0",
    "status": "RED"
  },
  {
    "id": "65:0",
    "status": "GREEN"
  },
  {
    "id": "65:0",
    "status": "GREEN"
  },
   {
    "id": "65:0",
    "status": "ORANGE"
  },
  {
    "id": "65:0",
    "status": "YELLOW"
  },
  {
    "id": "65:0",
    "status": "GREEN"
  }
] 

想要计算状态键值并创建以下对象

{
 'ORANGE' : 3,
 'GREEN' : 4,
 'YELLOW' : 2,
 'RED' : 1,
}

Answer 1

使用Array#reduce方法

var res = data.reduce(function(obj, v) {
  // increment or set the property
  // `(obj[v.status] || 0)` returns the property value if defined
  // or 0 ( since `undefined` is a falsy value
  obj[v.status] = (obj[v.status] || 0) + 1;
  // return the updated object
  return obj;
  // set the initial value as an object
}, {})

var data = [{
  "id": "65:0",
  "status": "ORANGE"
}, {
  "id": "65:0",
  "status": "GREEN"
}, {
  "id": "65:0",
  "status": "ORANGE"
}, {
  "id": "65:0",
  "status": "YELLOW"
}, {
  "id": "65:0",
  "status": "RED"
}, {
  "id": "65:0",
  "status": "GREEN"
}, {
  "id": "65:0",
  "status": "GREEN"
}, {
  "id": "65:0",
  "status": "ORANGE"
}, {
  "id": "65:0",
  "status": "YELLOW"
}, {
  "id": "65:0",
  "status": "GREEN"
}];

var res = data.reduce(function(obj, v) {
  obj[v.status] = (obj[v.status] || 0) + 1;
  return obj;
}, {})

console.log(res);

虽然您可以使用Array#forEach相同代码的方法.

var res = {};
data.forEach(function(v) {
  res[v.status] = (res[v.status] || 0) + 1;
})

var data = [{
  "id": "65:0",
  "status": "ORANGE"
}, {
  "id": "65:0",
  "status": "GREEN"
}, {
  "id": "65:0",
  "status": "ORANGE"
}, {
  "id": "65:0",
  "status": "YELLOW"
}, {
  "id": "65:0",
  "status": "RED"
}, {
  "id": "65:0",
  "status": "GREEN"
}, {
  "id": "65:0",
  "status": "GREEN"
}, {
  "id": "65:0",
  "status": "ORANGE"
}, {
  "id": "65:0",
  "status": "YELLOW"
}, {
  "id": "65:0",
  "status": "GREEN"
}];

var res = {};
data.forEach(function(v) {
  res[v.status] = (res[v.status] || 0) + 1;
})

console.log(res);