How to select array index after Where clause using Linq? How to select array index after Where clause using Linq? arrays arrays

How to select array index after Where clause using Linq?


c# linq arrays

You could do it this way:

weekDays.Select((day, index) => new { Day = day, Index = index })        .Where(x => x.Day.Contains("s"))        .Select(x => x.Index)        .ToArray();

Not sure if this is optimal..

c# linq arrays

Patko's answer is the way to go in the general case.

Here are 2 more options:

// Idea only works with collections that can be accessed quickly by index.int[] indices = Enumerable.Range(0, weekDays.Length)                          .Where(index => weekDays[index].Contains("s"))                          .ToArray();

With MoreLinq:

// Similar to Patko's idea, except using a 'named' type.int[] indices = weekDays.AsSmartEnumerable()                        .Where(item => item.Value.Contains("s"))                        .Select(item => item.Index)                        .ToArray();

c# linq arrays

This should work:

weekDays.Where(a => a.Contains("s")).Select((a, i) => i).ToArray();

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