Using the StringComparer class for string equality with C# .NET

In this post we saw how to use the generic IEqualityComparer of T interface to indicate equality for our custom types. If you need a similar comparer for strings then there’s a ready-made static class called StringComparer which can construct string comparers for you.

The StringComparer class provides comparers for the common string comparison scenarios: ordinal, locale specific and invariant culture comparisons. This is a good MSDN article on the differences between these.

Let’s first build a string list:

List<string> strings = new List<string>();
strings.Add("hello");
strings.Add("HELLO");
strings.Add("hELLO");
strings.Add("bye");
strings.Add("hello");
strings.Add("bye");
strings.Add("BYE");
strings.Add("byE");
strings.Add("HELLO");
strings.Add("BYE");

If you’d like to get the unique elements with casing taken into account you can write something like this:

List<string> uniqueStrings = strings.Distinct(StringComparer.InvariantCulture).ToList();

uniqueStrings will contain 6 elements.

However, if you’d like to perform a case-insensitive filtering then it’s equally easy:

List<string> uniqueStrings = strings.Distinct(StringComparer.InvariantCultureIgnoreCase).ToList();

uniqueStrings will now only contain 2 elements.

View all various C# language feature related posts here.

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About Andras Nemes
I'm a .NET/Java developer living and working in Stockholm, Sweden.

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