Retrieving Generic List Item index

Question

I have a list as below. I would like to retrieve the indexes of all the items which have the value 1.

        List<int> listFilter = new List<int>();

        listFilter.Add(1);
        listFilter.Add(0);
        listFilter.Add(0);
        listFilter.Add(1);

I should be getting 0 and 3 for the sample data above.

The code below gives me an object of [value, index] pair. How do I modify this to just output a list which has only the indexes.

        var val = listFilter.Select((value, index) => new { Value = value, Index = index }).Where(item => item.Value == 1).ToList();

Thanks

Regards, Balan Sinniah

Answer 1

The problem is that in the initial Select clause you returned an anonymous type. To get back out the value you need an additional Select later on to filter back to that value.

var val = listFilter
  .Select((value, index) => new { Value = value, Index = index })
  .Where(item => item.Value == 1)
  .Select(item => item.Index)
  .ToList();