Lets say we have a datagridview that is looking similar to this -

Question

Lets say we have a datagridview that is looking similar to this in c#:

I want that when I click the button, my program should look for uinique TaxRate and sum up the records so that I could get the following result using c#

Answer 1

You could use a Linq Sum() aggregate on a datatable column assuming you are using a datatable and show the results on the grid.

https://www.c-sharpcorner.com/article/calculate-the-sum-of-the-datatable-column-in-c-sharp/

https://learn.microsoft.com/en-us/dotnet/csharp/linq/

https://www.codecompiled.com/query-datatable-using-linq-in-csharp/

Answer 2

Here is a complete example which does grouping as asked. I didn't setup formatting of columns in the DataGridView.

Data class using mocked data

using System.Data;  
using System.Linq;  
  
namespace GroupbyDataTable  
{  
    public class Operations   
    {  
        public static DataTable Mocked()  
        {  
            var table = new DataTable();  
  
            table.Columns.Add(new DataColumn("TaxRate", typeof(decimal)));  
            table.Columns.Add(new DataColumn("Value", typeof(decimal)));  
            table.Columns.Add(new DataColumn("TaxAmount", typeof(decimal)));  
            table.Columns.Add(new DataColumn("FinalValue", typeof(decimal),   
                "Value + TaxAmount"));  
  
            table.Rows.Add(5, 1000, 50);  
            table.Rows.Add(5, 2000, 100);  
              
            table.Rows.Add(10, 1000, 100);  
            table.Rows.Add(10, 2000, 200);  
              
            table.Rows.Add(15, 1000, 150);  
            table.Rows.Add(15, 2000, 300);  
  
            return table;  
              
        }  
  
        public static DataTable GroupData(DataTable dt)  
        {  
  
            return dt.AsEnumerable()  
                .GroupBy(row => DataRowExtensions.Field<decimal>(row, "TaxRate"))  
                .Select(grouped =>  
                {  
                    var row = dt.NewRow();  
  
                    row["TaxRate"] = grouped.Key;  
                    row["Value"] = grouped.Sum(dRow => dRow.Field<decimal>("Value"));  
                    row["TaxAmount"] = grouped.Sum(dRow => dRow.Field<decimal>("TaxAmount"));  
                    row["FinalValue"] = grouped.Sum(dRow => dRow.Field<decimal>("FinalValue"));  
  
                    return row;  
                }).CopyToDataTable();  
        }  
    }  
}  

Form code

using System;  
using System.Data;  
using System.Windows.Forms;  
  
namespace GroupbyDataTable  
{  
    public partial class Form1 : Form  
    {  
        public Form1()  
        {  
            InitializeComponent();  
            Shown += OnShown;  
        }  
  
        private void OnShown(object sender, EventArgs e)  
        {  
            dataGridView1.DataSource = Operations.Mocked();  
        }  
  
        private void GroupButton_Click(object sender, EventArgs e)  
        {  
            dataGridView1.DataSource = Operations  
                .GroupData((DataTable)dataGridView1.DataSource);  
        }  
  
        private void ReloadButton_Click(object sender, EventArgs e)  
        {  
            dataGridView1.DataSource = Operations.Mocked();  
        }  
    }  
}