C#/Linq: Apply a mapping function to each element in an IEnumerable?

You can just use the Select() extension method:

IEnumerable<int> integers = new List<int>() { 1, 2, 3, 4, 5 };
IEnumerable<string> strings = integers.Select(i => i.ToString());

Or in LINQ syntax:

IEnumerable<int> integers = new List<int>() { 1, 2, 3, 4, 5 };

var strings = from i in integers
              select i.ToString();