Find sum of List where property == true?

Question

In my C# code, I have a list of type CustomClass. This class contains a boolean property trueOrFalse.

I have a List<CustomClass>. I wish to create an integer using this List which holds the number of objects in the list which have a trueOrFalse value of True.

What is the best way to do this ? I assume there is a clever way to use Linq to accomplish this, rather than having to iterate over every object ?

Thanks a lot.

Answer 1

You can use Enumerable.Count:

int numTrue = list.Count(cc => cc.trueOrFalse);

Remember to add using system.Linq;

Note that you should not use this method to check whether or not a sequence contains elements at all(list.Count(cc => cc.trueOrFalse) != 0). Therefore you should use Enumerable.Any:

bool hasTrue = list.Any(cc => cc.trueOrFalse);

The difference is that Count enumerates the whole sequence whereas Any will return true early as soon as it finds one element that passes the test predicate.

Answer 2

You can do that indeed simple with LINQ.

int amountTrue = list.Where(c => c.trueOrFalse).Count();

Or shorter with the Where in the count:

int amountTrue = list.Count(c => c.trueOrFalse);

Like Tim Schmelter stated: Add using System.Linq;