在C#中对DataTable进行分组，并使用Linq在新列中添加重复行

var groupedData = from row in dataTable.AsEnumerable()
                  group row by row.Field<string>("列名") into grp
                  select grp;

foreach (var group in groupedData)
{
    foreach (var row in group)
    {
        row["新列"] = group.Count();
    }
}

using System;
using System.Data;
using System.Linq;

class Program
{
    static void Main()
    {
        // 创建一个DataTable对象并添加数据
        DataTable dataTable = new DataTable();
        dataTable.Columns.Add("列名", typeof(string));
        dataTable.Rows.Add("A");
        dataTable.Rows.Add("A");
        dataTable.Rows.Add("B");
        dataTable.Rows.Add("C");
        dataTable.Rows.Add("C");

        // 对DataTable进行分组并添加重复行
        var groupedData = from row in dataTable.AsEnumerable()
                          group row by row.Field<string>("列名") into grp
                          select grp;

        foreach (var group in groupedData)
        {
            foreach (var row in group)
            {
                row["新列"] = group.Count();
            }
        }

        // 打印结果
        foreach (DataRow row in dataTable.Rows)
        {
            Console.WriteLine(row["列名"] + " " + row["新列"]);
        }
    }
}

A 2
A 2
B 1
C 2
C 2