How is it possible that selecting first after GroupBy on a DataTable does not return one value for e-CodePudding

I am trying to get one row per id from a DataTable, and I do not care which row I take. The same id can exist on several rows in the table.

Here's the expression that's giving me trouble:

dt.AsEnumerable().GroupBy(i => i.Field<int>("id")).Select(i => i.First())

Running just this section dt.AsEnumerable().GroupBy(i => i.Field<int>("id") correctly gives me a result of 22 groupings for my DataTable. (I have 22 ids with data in this table)

However, when adding on the .Select(i => i.First()), I am only seeing 10 data rows.

To me this doesn't seem to make any sense. If the GroupBy function managed to find 22 distinct id values, I would expect this logic to grab one of each.

My only other thought is that maybe it's just a weird side effect of viewing this data through a watch in Visual Studio rather than assigning to a variable.

CodePudding user response：

If you think it's just weird side effects of viewing the data in a watch, which can happen with LINQ statements, then split it out into

var groups = dt.AsEnumerable().GroupBy(i => i.Field<int>("id")).ToList();
var firstOfGroups = groups.Select(i => i.First()).ToList();

and then look at groups and firstOfGroups in the debugger. Temporarily evaluating items with .ToList() can help a lot with viewing things in the debugger.

CodePudding user response：

I think it is possible, can double check the count of each group items

.Select(g=>new { k = g.Key, c = g.Count() })