如何在c＃.net中按arraylist分组 [英] How to group by arraylist in c#.net

问题描述

我有一个带有以下数据的arrayList作为一个字符串，它被分隔;在c＃.net中我想计算特殊日期时间内每个ID的类型我该怎么做

I have a arrayList with below data as a string which is seperated by ; in c#.net.I want to count type for each ID in a special datetime How can I do this

ArrayList arrn = new ArrayList();

"1;2017-2-3 08:21:03;type1"
"1;2017-2-4 08:21:03;type1"
"1;2017-2-4 08:21:03;type1"
"2;2017-2-3 08:21:03;type1"
"2;2017-2-3 08:21:03;type1"
"3;2017-2-3 08:21:03;type1"

请帮我分组这个arraylist来计算类型在每个ID的特殊日期时间



我尝试过：



我在互联网上搜索了很多但是我没有成功

please help me to group by this arraylist to count types in a special datetime for each ID

What I have tried:

I searched a lot in internet but I was not successful

推荐答案

你应该使用 List< T> 代替 ArrayList [ ^ ]。



为了能够按id分组数据，你必须创建自定义对象，例如：

You should use List<T> instead of ArrayList[^].

To be able to group data by id, you have to create custom object, for example:

public class MyObject
{
	public int Id {get; set;}
	public DateTime Dt {get; set;}
	public string sType {get; set;}
}

现在，您必须创建 List< MyObject> ，能够通过 arrn 对象的项目并将它们转换为 MyObject的列表 ：

Now, you have to create List<MyObject>, to be able to go though the items of arrn object and convert them into a List of MyObject:

List<MyObject> mydata = new List<MyObject>();

foreach(string x in arrn)
{
    mydata.Add(new MyObject
        {
            Id = Convert.ToInt32(x.Split(new string[]{";"}, StringSplitOptions.RemoveEmptyEntries)[0]),
            Dt = Convert.ToDateTime(x.Split(new string[]{";"}, StringSplitOptions.RemoveEmptyEntries)[1]),
            sType = x.Split(new string[]{";"}, StringSplitOptions.RemoveEmptyEntries)[2]
        });
}

最后，您已准备好使用 Linq [ ^ ]对数据进行分组和统计：

Finally, you're ready to use Linq[^] to group and count data:

var result = mydata
    .GroupBy(x=>x.Id)
    .Select(grp=> new
        {
            Id = grp.Key,
            Count = grp.Count()
        })
    .ToList();

结果：

Result:

Id Count
1  3 
2  2 
3  1 

最好的办法是：

1）停止使用ArrayList - 它被泛型集合取代在.NET的.NET中！

2）创建一个类来保存值，并给它一个带字符串的构造函数。



首先，使用string拆分每个字符串.Split：

然后使用DateTime.TryParseExact将每个日期转换为DateTime值，并使用intTryParse转换ID：

The best things to do are:
1) Stop using ArrayList - it was superseded by generic collections in V2 of .NET!
2) Create a class to hold the values, and give it a constructor which takes a string.

First, split each string using string.Split:
Then use DateTime.TryParseExact to convert each date to a DateTime value, and intTryParse to convert the ID:

private class MyData
            {
            private int _ID;
            public int ID
                {
                get { return _ID; }
                set { _ID = value; }
                }
            private DateTime _Date;
            public DateTime Date
                {
                get { return _Date; }
                set { _Date = value; }
                }
            private string _Type;
            public string Type
                {
                get { return _Type; }
                set { _Type = value; }
                }
            public MyData(string s)
                {
                string[] parts = s.Split(';');
                if (parts.Length != 3) throw new ArgumentException("Not a valid MyData element: " + s);
                if (!int.TryParse(parts[0], out _ID)) throw new ArgumentException("Bad ID Value: " + parts[0]);
                if (!DateTime.TryParseExact(parts[1], "yyyy-M-dd HH:mm:ss", CultureInfo.InvariantCulture, DateTimeStyles.None, out _Date)) throw new ArgumentException("Bad date format: " + parts[1]);
                _Type = parts[2];
                }
            }

使用每个字符串生成一个新的MyData实例，并将它们存储在List< MyData>

然后它是非常简单的使用Linq查询（甚至是foreach循环）来获取按日期，ID或两者分组的总计。

Use each string to generate a new instance of MyData, and store them in a List<MyData>
Then it's pretty trivial to use a Linq query (or even a foreach loop) to get the totals grouped by date, ID, or both.

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