C# Syntax - Split String into Array by Comma, Convert To Generic List, and Reverse Order


Question

What is the correct syntax for this:

IList<string> names = "Tom,Scott,Bob".Split(',').ToList<string>().Reverse();

What am I messing up? What does TSource mean?

1
85
11/24/2008 8:30:50 PM

Accepted Answer

The problem is that you're calling List<T>.Reverse() which returns void.

You could either do:

List<string> names = "Tom,Scott,Bob".Split(',').ToList<string>();
names.Reverse();

or:

IList<string> names = "Tom,Scott,Bob".Split(',').Reverse().ToList<string>();

The latter is more expensive, as reversing an arbitrary IEnumerable<T> involves buffering all of the data and then yielding it all - whereas List<T> can do all the reversing "in-place". (The difference here is that it's calling the Enumerable.Reverse<T>() extension method, instead of the List<T>.Reverse() instance method.)

More efficient yet, you could use:

string[] namesArray = "Tom,Scott,Bob".Split(',');
List<string> namesList = new List<string>(namesArray.Length);
namesList.AddRange(namesArray);
namesList.Reverse();

This avoids creating any buffers of an inappropriate size - at the cost of taking four statements where one will do... As ever, weigh up readability against performance in the real use case.

235
11/24/2008 9:05:21 PM

I realize that this question is quite old, but I had a similar problem, except my string had spaces included in it. For those that need to know how to separate a string with more than just commas:

string str = "Tom, Scott, Bob";
  IList<string> names = str.Split(new string[] {","," "},
  StringSplitOptions.RemoveEmptyEntries);

The StringSplitOptions removes the records that would only be a space char...


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