Linq .Any VS .Exists - What's the Difference

LINQ .Any VS .Exists - What's the difference?

See documentation

List.Exists (Object method - MSDN)

Determines whether the List(T) contains elements that match the conditions defined by the specified predicate.

This exists since .NET 2.0, so before LINQ. Meant to be used with the Predicate delegate, but lambda expressions are backward compatible. Also, just List has this (not even IList)

IEnumerable.Any (Extension method - MSDN)

Determines whether any element of a sequence satisfies a condition.

This is new in .NET 3.5 and uses Func(TSource, bool) as argument, so this was intended to be used with lambda expressions and LINQ.

In behaviour, these are identical.

LINQ Any vs Exists Performance

Exists requires an instance of List<T> while Any is invoked on IEnumerable<T>. This means you have the potential for increased memory efficiency as IEnumerable<T> can be evaluated lazily.

LINQ extension methods - Any() vs. Where() vs. Exists()

Where returns a new sequence of items matching the predicate.

Any returns a Boolean value; there's a version with a predicate (in which case it returns whether or not any items match) and a version without (in which case it returns whether the query-so-far contains any items).

I'm not sure about Exists - it's not a LINQ standard query operator. If there's a version for the Entity Framework, perhaps it checks for existence based on a key - a sort of specialized form of Any? (There's an Exists method in List<T> which is similar to Any(predicate) but that predates LINQ.)

What is the difference between Contains and Any in LINQ?

Contains takes an object, Any takes a predicate.

You use Contains like this:

listOFInts.Contains(1);

and Any like this:

listOfInts.Any(i => i == 1);
listOfInts.Any(i => i % 2 == 0); // Check if any element is an Even Number

So if you want to check for a specific condition, use Any. If you want to check for the existence of an element, use Contains.

MSDN for Contains, Any

Linq Any() vs MoveNext()

Since IEnumerator<T> implements IDisposable (and thus can allocate resources) you have to put (in general case) not a simple line

// Don't do this: it can cause a resource leakage
HasChild = Childs.GetEnumerator().MoveNext() ? true : false;

but a fragment

bool HasChild = false;

using (var en = Childs.GetEnumerator()) {
  HasChild = en.MoveNext(); // You have no need in ternary operator here
}

And it seems too wordy when in case of Any all you should do

bool HasChild = Childs.Any();

And Enumerable<T>.Any will do the wordy part for you:

http://referencesource.microsoft.com/#System.Core/System/Linq/Enumerable.cs,8788153112b7ffd0

    public static bool Any<TSource>(this IEnumerable<TSource> source) {
        if (source == null) throw Error.ArgumentNull("source");
        using (IEnumerator<TSource> e = source.GetEnumerator()) {
            if (e.MoveNext()) return true;
        }
        return false;
    }

What are the difference between .Select, .Any, and .Count when using LINQ

Count needs to iterate the entire collection, because it (obviously) needs to count the number of instances.

Any finds the first occurrence & returns true or false. If there aren't any, then it needs to iterate the whole collection to try to find, but if the first instance matches then it only needs to check the first instance.

Select is completely different. It is used to project a collection into another collection. It does not perform any checking or filtering.

edit: In SQL terms, Any is like Exists, while Count is like Count(*).

If I want to know whether there are any people on the street today, it is completely unnecessarily to count all the people and see if the number is >= 1. As soon as I find one person then I'm done.

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