Question

I want to return all of the indices from an array where a condition is met. I’ve come up with

myarray
   .Select((p,i) => 
       {              
          if (SomeCondition(p)) return i; 
          else return -1;
       })
   .Where(p => p != -1);

I know I can write an extension method or do it with a loop, but I was wondering if there was something built into LINQ that I’m unfamiliar with. Apologies if this is trivial

Answer 1

Personally, I’d go with this:

myarray
    .Select((p, i) => new { Item = p, Index = i })
    .Where(p => SomeCondition(p.Item))
    .Select(p => p.Index);