Question

How can I get an array of datatable row numbers which meet a certain criteria? For example I have a datatable with a column “DateTime”. I want to retrieve the row numbers of the datatable where “DateTime” equals the variable startTime.

I know how to retrieve the actual row, but not the number of the row in the datatable.

Any help will be appreciated 🙂

Answer 1

If I am reading the question right, using the overload of Select that allows a second input for the index may work for you. Something like

var indices = 
    table.AsEnumerable()
         .Select((row, index) => new { row, index })
         .Where(item => item.row.Field<DateTime?>("DateTime") == startTime)
         .Select(item => item.index)
         .ToArray();

If that date matches on the first, third, and sixth rows, the array will contain indices 0, 2, and 5. You can, of course, add 1 to each index in the query if you would like row numbers to start at 1. (ex: .Select(item => item.index + 1))