lodash：从对象数组中计算值

Question

我有一个像这样的对象数组：

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

我想按问题键分组并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
    }]
}

,

我可以使用groupBy问题： .groupBy("question")并使用.countBy()计算值的出现次数，但我不确定如何组合分组和计数功能来实现所需的输出？

Answer 1

您可以从_.groupBy(array, 'question') - 然后使用.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));

查看工作版本： http : //jsbin.com/wixoronoqi/edit?js,console

Answer 2

这是针对此问题的本机/vanilla js 解决方案，使用Array.reduce() ，带有和不带有扩展运算符。

使用扩展运算符，不可变样式：

 const questions = [ {"question":"Q1","answer":"my answer 2"}, {"question":"Q1","answer":"my answer"}, {"question":"Q1","answer":"my answer"}, {"question":"Q2","answer":"answer 2"} ]; const groupedQuestions = questions.reduce( (g, q) => { return { ...g, [q.question]: { ...g[q.question], [q.answer] : (g[q.question] && g[q.question][q.answer] || 0) + 1 } } }, {}) document.write(JSON.stringify(groupedQuestions))

没有传播运算符：

 const questions = [ {"question":"Q1","answer":"my answer 2"}, {"question":"Q1","answer":"my answer"}, {"question":"Q1","answer":"my answer"}, {"question":"Q2","answer":"answer 2"} ]; const groupedQuestions = questions.reduce( (g, q) => { typeof g[q.question] !== "undefined" || (g[q.question] = {}); typeof g[q.question][q.answer] !== "undefined" || (g[q.question][q.answer] = 0); g[q.question][q.answer] += 1; return g; }, {}) document.write(JSON.stringify(groupedQuestions))

Answer 3

使用Array.forEach和Array.push函数的“原生 javascript”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
        }
    ]
}