如何按月对一组对象进行分组？ [英] How can I group an array of objects by month?

问题描述

我正在使用JavaScript。我有一个包含这种格式数据的数组：

  [
 {USER_NAME：User1， LAST_SUCCESSFUL_CONNECT：1373978337642，
 {USER_NAME：User2，LAST_SUCCESSFUL_CONNECT：1374515704026}，
 {USER_NAME：User3，LAST_SUCCESSFUL_CONNECT：1374749782479 （上面的数字表示以毫秒为单位的UTC日期/时间。）
 
 
 
 
我想按月对数据进行分组（计数），如下所示： 
 
 
  {Month：2014年1月，User_Count：2}，
 {Month：2014年2月，User_Count：1}，
 
  
我可以使用 jQuery 如果它简化了一些事情。   

map reduce 问题。高级解决方案如下：



1. 重新组织这个memb


$ b

以下是一步一步的介绍如何实现这一点：



Map






1. 遍历字典列表


2. 将datetime字符串转换为javascript datetime对象。


3. 使用month-year作为键和词典列表作为值。



现在按月份分组。



例子：



  var l = [...]; 
 var o = {}; 
 var f = function（x）{
 var dt_object = Date（x [LAST_SUCCESSFUL_CONNECT]）; //转换为datetime对象
 var key = dt_object.year +' - '+ dt_object.month; 
 
 if（o [key] === undefined）{
 var o [key] = []; 
}; 
 $ b $ [b] bush（x）
} 
 
 _.map（l，f（x））//将f应用于l 
  





减少






1. 迭代包含列表字典的新对象。


2. 计算每个字典列表的长度。


3. 使用 count 作为键值和列表长度作为其值。



示例：

  var g = function（member_count）{
 //额外的逻辑可能会在这里
返回member_count 
} 
 
用于o {
 count = _.reduce（l，g（成员））
成员['count'] = count 
} 
  





结果API





  o ['month-year'] //当月字典清单
o ['month-year'] ['count'] //用于该月字典列表的计数。 
  





参考文献：





在javascript中为 map 和 reduce 函数请参阅underscore.js：

http://underscorejs.org/#map

http://underscorejs.org/#reduce





Javascript日期对象：

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date





有关Date和DateTime对象的更多信息：

https://en.wikipedia.org/wiki/ISO_8601





有关 map 的更多信息， code> reduce ：

https：/ /en.wikipedia.org/wiki/MapReduce




I'm using JavaScript. I have an array that contains data in this format:

[
        {"USER_NAME":"User1","LAST_SUCCESSFUL_CONNECT":"1373978337642"},
        {"USER_NAME":"User2","LAST_SUCCESSFUL_CONNECT":"1374515704026"},
        {"USER_NAME":"User3","LAST_SUCCESSFUL_CONNECT":"1374749782479"}
]

(the numbers above represent UTC date/time in milliseconds.

I would like to group (count) the data by month. Something like this:

[
    {"Month":"January, 2014","User_Count": 2},
    {"Month":"February, 2014","User_Count": 1},
]

I could use jQuery if it simplifies matters.

解决方案

This looks like a map reduce problem. The high-level solution is as follows:

1. Re-organize the members of the list.
2. Count them.

Here is a step-by-step how-to for achieving this:

Map

1. Iterate through the list of dictionaries
2. Convert datetime string to javascript datetime object.
3. Use month-year as key and list of dictionaries as value.

These are now grouped by month-year.

Example:

var l = [...];
var o = {};
var f = function(x){
    var dt_object = Date(x["LAST_SUCCESSFUL_CONNECT"]); // convert to datetime object
    var key = dt_object.year + '-' + dt_object.month;

    if (o[key] === undefined) {
        var o[key] = [];
    };

    o[key].push(x)
}

_.map(l, f(x)) //apply f to each member of l

Reduce

1. Iterate through the new object containing dictionaries of lists.
2. Calculate length of each dictionary's list.
3. Use count as key and length of list as its value.

Example:

var g = function(member_count){
    //extra logic may go here
    return member_count
}

for member in o {
    count = _.reduce(l, g(member))
    member['count'] = count
}

Resulting API

o['month-year'] //for list of dictionaries in that month
o['month-year']['count'] //for the count of list of dictionaries in that month.

References:

For map and reduce functions in javascript see underscore.js:
http://underscorejs.org/#map
http://underscorejs.org/#reduce

Javascript Date object:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date

For more information on Date and DateTime objects:
https://en.wikipedia.org/wiki/ISO_8601

For more information on map reduce:
https://en.wikipedia.org/wiki/MapReduce

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