Linq & Boolean Function

Question

Is there any way one can apply a function with signature

bool IsOdd(int number);

to an array of integers and return whether any given integer in that array is odd in a single instruction? I know I can use

return (array.Where(IsOdd).Count() > 0);

but that implies calling two methods and making a comparison... Isn't there really a shorter way to achieve the same?

Answer 1

Yes.

To start with you could use the form of Count which takes a predicate:

return array.Count(IsOdd) > 0;

... but you don't want to do that. That code is still expressing a numerical comparison which is unnecessary. You want to ask if any item in the array is odd. In other words:

return array.Any(IsOdd);

Not only is this more expressive - it's also potentially much faster. As soon as Any finds a match, it will return true - whereas Count would have to iterate over the whole array to find out exactly how many matches there are.

Basically, whenever you see a LINQ query using Count() > 0 you should think about using Any instead. In some cases with expression-tree-based queries such as LINQ to SQL it may not make a performance difference (if the query optimizer has visibility of the comparison with 0) but in LINQ to Objects it certainly can.