.NET Predicates (and a .RemoveAll() example)

May 25th, 2007 by Sameer | Filed under .NET articles.

A predicate is a function that returns true or false and can be used for example to filter your results.. For example your .NET RemoveAll(…) function can actually do things like:

Remove all records that say …

  • "start with S"
  • or "are 5 letters long"
  • etc etc..
  • whatever you wanna do.. GO WILD!

And knowing this, plus using our .NET 2.0 anonymous methods, we can do the above filtering in a single line!  We don’t even need to write a special predicate function.

For example if you have a general list of ints, and you want to remove all ints that are equal to the value 5, you can do the following:

yourList.RemoveAll(new System.Predicate<int>( delegate(int val) { return (val == 5); }));

The keyword delegate(int val) { … } allows you to create an anonymous method.

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