Question

Is there a better way to do this?

string[] s = {'zero', 'one', 'two', 'three', 'four', 'five'};  var x =  s .Select((a,i) => new {Value = a, Index = i}) .Where(b => b.Value.StartsWith('t')) .Select(c => c.Index); 

i.e. I’m looking for a more efficient or more elegant way to get the positions of the items matching the criteria.

Answer 1

You could easily add your own extension method:

public static IEnumerable<int> IndexesWhere<T>(this IEnumerable<T> source, Func<T, bool> predicate) {     int index=0;     foreach (T element in source)     {         if (predicate(element))         {             yield return index;         }         index++;     } } 

Then use it with:

string[] s = {'zero', 'one', 'two', 'three', 'four', 'five'}; var x = s.IndexesWhere(t => t.StartsWith('t'));