Compare values of datatable and remove duplicate

Question

Hi. I have a data table with few columns. F some of the columns, I have some duplicate values.

col1	col2	col3
Region	cell2	Cell 2
Region	cell2	Cell 4
Green	cell3	cell5
Green	cell3	cell7

For example: I want to compare the col1 values and then keep the datatable as below. How to achieve this ?

col1	col2	col3
Region	cell2	Cell 2
	cell2	Cell 4
Green	cell3	cell5
	cell3	cell7

Thanks

Answer 1

Hi @Padmanabhan, Venkatesh ，welcome to Microsoft Q&A.

You could directly add a null value directly from the second line when creating it.

You could create a HashSet<string>. Start traversing from the first row, if the current row value is not in it, keep it and save it in HashSet; if it exists, make it empty.

The specific code is as follows:

DataTable dt = new DataTable();
dt.Columns.Add("col1");
dt.Columns.Add("col2");
dt.Columns.Add("col3");
dt.Rows.Add("Region", "Cell 2", "XXXX 3");
dt.Rows.Add("Region", "Cell 5", "XXXX 4");
dt.Rows.Add("Region", "Cell 6", "XXXX 7");
dt.Rows.Add("Green", "cell5", "XXXX 8");
dt.Rows.Add("Green", "cell7", "XXXX 9");
HashSet<string> seenCol1Values = new HashSet<string>();
for (int i = 0; i <= dt.Rows.Count - 1; i++)
{
    DataRow row = dt.Rows[i];
    string col1Value = row["col1"].ToString();
    if (seenCol1Values.Contains(col1Value))
    {
        row["col1"] = DBNull.Value;
    }
    else
    {
        seenCol1Values.Add(col1Value);
    }
}
dataGridView1.DataSource = dt;

Best Regards,

Jiale

---

If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment". 

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.