Question

I have a data set something like this:

2,Black
2,Blue
2,Red
1,Small
1,Medium

I need to convert this into the following:

2_0
2_1
2_2
1_0
1_1

The LINQ query I have at the moment uses an index for the second number, however it doesn’t reset to 0 when changing from 2_ to 1_. I’ve tried using a GroupBy, but I can’t get the results I need – can anyone help?

Answer 1

IEnumerable<string> output = input
    .GroupBy(i => i.Num)
    .SelectMany(grp => grp.Select((item, idx) => string.Format("{0}_{1}", grp.Key, idx)));