Question

I have a large DataTable – around 15000 rows and 100 columns – and I need to set the values for some of the columns in every row.

// Creating the DataTable
DataTable dt = new DataTable();
for (int i = 0; i < COLS_NUM; i++)
{
    dt.Columns.Add("COL" + i);
}    
for (int i = 0; i < ROWS_NUM; i++)
{
    dt.Rows.Add(dt.NewRow());
}

// Setting several values in every row
Stopwatch sw2 = new Stopwatch();
sw2.Start();
foreach (DataRow row in dt.Rows)
{
    for (int j = 0; j < 15; j++)
    {
        row["Col" + j] = 5;
    }
}
sw2.Stop();

The measured time above is about 4.5 seconds. Is there any simple way to improve this?

Answer 1

One improvement that I can think of is editing columns by their indices, rather than their names.

foreach (DataRow row in dt.Rows)
{
    for (int j = 0; j < 15; j++)
    {
        row[j] = 5;
    }
}

With an empirical test, your method seems to run in ~1500 milliseconds on my computer, and this index based version runs in ~1100 milliseconds.

Also, see Marc’s answer in this post:

Set value for all rows in a datatable without for loop