Foreach loop, determine which is the last iteration of the loop - DataRow

Question

Please take a look at this link.
Now i have a foreach like this :

//DataRow last = dsRequests.Tables["Requests"].Rows.Last();

foreach (DataRow drRequests in dsRequests.Tables["Requests"].Rows)
{
}

I want to determine the last iteration of the foreach loop.
So i tried this :

DataRow last = dsRequests.Tables["Requests"].Rows.Last();

But I have this error:

Error CS1061 'DataRowCollection' does not contain a definition for 'Last' and no extension method 'Last' accepting a first argument of type 'DataRowCollection' could be found (are you missing a using directive or an assembly reference?)

How can I do that?

Steve · Accepted Answer · 2019-03-17T18:07:25.893

You can simply write

 DataRow last = dsRequests.Tables["Requests"].AsEnumerable().LastOrDefault();
 if(last != null)
     .....

forcing the DataTable to be enumerable then you can use LastOrDefault(). Notice that I am using LastOrDefault because, if the table is empty, Last() will get you an exception.

Another approach is through the old fashioned index over the Rows collection

    DataRow last = null;
    int idx = dsRequests.Tables["Requests"].Rows.Count;
    if(idx > 0) last = dsRequests.Tables["Requests"].Rows[idx -1];
    if(last != null)
        ....

In this example you have to test the number of rows after getting the count.

I should also add that the last example using the index to access the last row is more performant. However my tests show that on a 100000 loop the difference is simply 40 millisecs. Nothing to worry about.

Foreach loop, determine which is the last iteration of the loop - DataRow

1 Answers1