lodash：从对象的数组计数值

Question

我有对象的一个​​这样的数组：

[ 
{"question":"Q1","answer":"my answer 2"}, 
{"question":"Q1","answer":"my answer"} 
{"question":"Q1","answer":"my answer"} 
{"question":"Q2","answer":"answer 2"} 
] 

我想按的问题键和返回每个答案的计数。

例如

{ 
    "Q1": [{ 
     "answer": "my answer", 
     "count": 2 
    }, { 
     "answer": "my answer 2", 
     "count": 1 
    }], 
    "Q2": [{ 
     "answer": "answer 2", 
     "count": 1 
    }] 
} 

，

我能够groupBy问题使用：使用.countBy()值 .groupBy("question")和计数occurances但我不知道如何分组合并及计数功能，以实现所需的输出？

Answer 1

您可以_.groupBy(array, 'question')开始 - 然后用.map

例如：

var arr = [ 
{"question":"Q1","answer":"my answer 2"}, 
{"question":"Q1","answer":"my answer"}, 
{"question":"Q1","answer":"my answer"}, 
{"question":"Q2","answer":"answer 2"} 
]; 

var result = _(arr) 
    .groupBy('question') 
    .map(function(item, itemId) { 
    var obj = {}; 
    obj[itemId] = _.countBy(item, 'answer') 
    return obj 
    }).value(); 

console.log(JSON.stringify(result, null, 2)); 

参见工作版本在：http://jsbin.com/wixoronoqi/edit?js,console

Answer 2

使用Array.forEach和Array.push功能的 “本地JavaScript” 的解决方案：

var arr = [{"question":"Q1","answer":"my answer 2"},{"question":"Q1","answer":"my answer"}, {"question":"Q1","answer":"my answer"}, {"question":"Q2","answer":"answer 2"}]; 

var result = {}; 
arr.forEach(function(v){ 
    var key = v['question'], Q = this[key], found = false; 
    if (Q) { 
     var len = Q.length; 
     while (len--) { 
      if (Q[len]['answer'] === v['answer']) { 
       Q[len]['count']++; 
       found = true; 
      } 
     } 
     if (!found) Q.push({'answer': v['answer'], 'count' : 1}); 
    } else { 
     this[key] = []; 
     this[key].push({'answer': v['answer'], 'count' : 1}); 
    } 
}, result); 

console.log(JSON.stringify(result, 0, 4)); 

输出：

{ 
    "Q1": [ 
     { 
      "answer": "my answer 2", 
      "count": 1 
     }, 
     { 
      "answer": "my answer", 
      "count": 2 
     } 
    ], 
    "Q2": [ 
     { 
      "answer": "answer 2", 
      "count": 1 
     } 
    ] 
}