c# Array.FindAllIndexOf which FindAll IndexOf

Question

I know c# has Array.FindAll and Array.IndexOf.

Is there a Array.FindAllIndexOf which returns int[]?

Answer 1

string[] myarr = new string[] {"s", "f", "s"};  int[] v = myarr.Select((b,i) => b == "s" ? i : -1).Where(i => i != -1).ToArray(); 

This will return 0, 2

If the value does not exist in the array then it will return a int[0].

make an extension method of it

public static class EM {     public static int[] FindAllIndexof<T>(this IEnumerable<T> values, T val)     {         return values.Select((b,i) => object.Equals(b, val) ? i : -1).Where(i => i != -1).ToArray();     } } 

and call it like

string[] myarr = new string[] {"s", "f", "s"};  int[] v = myarr.FindAllIndexof("s"); 

Answer 2

You can write something like :

string[] someItems = { "cat", "dog", "purple elephant", "unicorn" };  var selectedItems = someItems.Select((item, index) => new{     ItemName = item,     Position = index}); 

or

var Items = someItems.Select((item, index) => new{     ItemName = item,     Position = index}).Where(i => i.ItemName == "purple elephant"); 

Read : Get the index of a given item using LINQ