使用map函数在Javascript中创建关联数组

I've an array of objects with the following format

我有一个具有以下格式的对象数组

[{'list': 'one', 'item': 1}, 
 {'list': 'one', 'item': 2},
 {'list': 'one', 'item': 3},
 {'list': 'two', 'item': 1},
 {'list': 'two', 'item': 2}]

And I want to transform it like this

我想像这样改造它

[{'one': [1, 2, 3]},
 {'two': [1, 2]}]

How can i do it using Array.map function? It's the best alternative?

我怎么能用Array.map函数呢？这是最好的选择吗？

3 个解决方案

#1

To your specific question:

针对您的具体问题：

// Let x hold your array of objects.

res={}; // Create an empty object that will hold the answer

x.forEach (function (e) { // Use this function to iterate over each item in the list
    res[e.list] = res[e.list] || [];   // inspired by the Nina Scholz answer below
    res[e.list].push(e.item);   // Append the result to the array
 });

#2

You may use Array.prototype.reduce for your task. It allows a return value in the callback function for the next call.

您可以使用Array.prototype.reduce来完成任务。它允许回调函数中的返回值用于下一次调用。

var data = [
        { 'list': 'one', 'item': 1 },
        { 'list': 'one', 'item': 2 },
        { 'list': 'one', 'item': 3 },
        { 'list': 'two', 'item': 1 },
        { 'list': 'two', 'item': 2 }
    ],
    flat = data.reduce(function (r, a) {
        r[a.list] = r[a.list] || [];
        r[a.list].push(a.item);
        return r;
    }, {});

document.write('<pre>' + JSON.stringify(flat, 0, 4) + '</pre>');

#3

What you're looking for is a group-by method. This question has a nice answer: https://codereview.stackexchange.com/questions/37028/grouping-elements-in-array-by-multiple-properties

您正在寻找的是一种分组方法。这个问题有一个很好的答案：https：//codereview.stackexchange.com/questions/37028/grouping-elements-in-array-by-multiple-properties

The code:

代码：

function groupBy( array , f )
{
  var groups = {};
  array.forEach( function( o )
  {
    var group = JSON.stringify( f(o) );
    groups[group] = groups[group] || [];
    groups[group].push( o );  
  });
  return Object.keys(groups).map( function( group )
  {
    return groups[group]; 
  })
}

var result = groupBy(list, function(item)
{
  return [item.lastname, item.age];
});

#1