What's the use of .Any() in a C# List<>?

Question

I've been discussing this with colleagues, and we couldn't figure out what the use is of .Any for any given List<>, in C#.

You can check the validity of an element in the array like the following statement:

if (MyList.Any()){ ...}  //Returns true or false

Which is exactly the same as

if (MyList.Count() != 0) { ... }

and is much more common, readable and clear about the intent of the if statement.

In the end, we were stuck with this thought:

.Any() can be used, will work just as well, but is less clear about the intent of the programmer, and it that case it should not be used.

But we feel like this can't be right; we must be missing something.

Are we?

I challenge your claim that `Any()` is less clear: `Any()` seems more clear to me, especially with a lambda-condition. Translating code to English in my head, `if(MyList.Count(o => o > 10) > 0)` becomes _"Is the number of items greater than 10 more than 0?"_ whereas `if(MyList.Any(o => o > 10))` becomes _"Are there any items greater than 10?"_ — BlueRaja - Danny Pflughoeft, Sep 04 '15 at 21:32
In some regards, these functions are not well-named. In C++, it would have been `if (!list.empty())`, which seems more related to a list being empty or not. While I am not usually into negating things, `list not empty` is clearer to me than `list any`. Surely, if you insert a `list _has_ any`, it's clearer. But then, Any also has other meanings, e.g. "any true", and you have to put it in mentally, already knowing what "Any" does. — phresnel, Sep 05 '15 at 06:18
they are not well-named because they are trying to mimic SQL. (select instead of map, aggregate instead of fold, where instead of filter, etc.); in Haskell this is a lot better. — Display Name, Sep 05 '15 at 07:29
@SargeBorsch - only if you prefer Heskel/functional naming, which most people don't. — Davor Ždralo, Sep 05 '15 at 08:14
@BlueRaja-DannyPflughoeft i agree. I think any is more clear since it eliminates a what could be considered a magic number. — Andy, Sep 05 '15 at 19:49
@SargeBorsch: The SQL parallel to `Any` is `Exists`. The Linq name is probably more inspired by Haskell and Python which also have any/all functions. — JacquesB, Sep 06 '15 at 11:53
@phresnel: Empty() works when there is no predicate but reads really strange when a predicate is supplied. Any() works in both cases and have a nice symmetry with All(), and the Any()/All() pair have precedence in other languages. — JacquesB, Sep 06 '15 at 11:58
@JacquesB: Personally, I associate any/none/all with checking for a condition _on_ a list, but not with the meaning of "has any". Probably because there is no symmetry between "list.empty"=="list *is* empty", and "list.any"=="list *has* any". Whereas upon a list, it reads "if any true in list", "if none true in list", "if all true in list". I guess it's that symmetry that makes it less intuitive to me. Personally, while I find it uglier, but I think I would prefer if they'd just stick to "list.hasXXX", "list.isXXX" naming convention, looks less leet, but is less ambiguous. — phresnel, Sep 07 '15 at 07:46
With 3 more years of experience behind me (it was my second year of development back in 2015), I do not have the same point of view I had back in the day. After re-reading the question I wrote, I now completely disagree with the intent being unclear. — Gil Sand, Oct 23 '18 at 09:23
@KolobCanyon Because on stackoverflow the answer would've been one single line explaining what Any actually does, and not my actual question which is "why would you do it" and not "what does it do ?" — Gil Sand, Jan 31 '19 at 15:02

Mason Wheeler · Accepted Answer · 2015-09-04T18:30:54.243

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Keep in mind that Any doesn't operate on a List; it operates on an IEnumerable, which represents a concrete type that may or may not have a Count property. It's true that it's not necessarily the best thing to use on a List, but it definitely comes in handy at the end of a LINQ query. And even more useful than the standalone version is the override that takes a predicate just like Where. There's nothing built in on List that's anywhere near as convenient or expressive as the predicate-Any extension method.

Also, if you're using Count() (the LINQ extension method for IEnumerable), rather than Count (the property on List), it can have to enumerate the entire sequence if it can't optimize this away by detecting that your underlying data type has a Count Property. If you have a long sequence, this can be a noticeable performance hit when you don't really care about what the count is, and just want to know if there are any items in the collection.

edited Sep 04 '15 at 18:30

answered Sep 04 '15 at 18:21

Mason Wheeler

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This. Performance aside, `Any()` with a predicate is *more* expressive than comparing the override of `Enumerable.Count()` that takes a predicate with 0. :) – Dan J Sep 04 '15 at 19:54
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I think this explains the fundamentals so clearly that explains the answer at best. – Tarik Sep 08 '15 at 16:44
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IMHO, `Exists` is just as convenient and expressive as `Any`, with a predicate. Using `Count != 0` property on a `List` is more normal than using `Any()`. It's just personal preference. I've also gone through the effort of changing `_list_.Count()` to `_list_.Count` in my group's code. It made a noticeable difference to me. – Suncat2000 May 25 '17 at 14:43

score 61 · Answer 2 · answered Sep 04 '15 at 18:26

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There is a run time difference Count() can be O(n) where Any() is O(1).

answered Sep 04 '15 at 18:26

Sign

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`Count()` also will not halt for infinite iterators, while `Any()` will, since it only needs to call `MoveNext()` once. – Jon Purdy Sep 04 '15 at 18:31
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Succinct and accurate, but this reads more as a comment than an answer. Programmers prefers answers that delve into the _why_ and providing a measure of explanation. Consider [edit]ing your answer and expanding upon why O(1) might be (is) important. – Sep 04 '15 at 18:40
very good answer just learned i should use any instead of count==0 :d – Furkan Gözükara Sep 04 '15 at 18:59
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`Any(Func)` is O(n) – BlueRaja - Danny Pflughoeft Sep 04 '15 at 21:34
This isn't always true. It depends on the concrete type you call it on, but I can never remember which ones it's not true for. IIRC though, it's never *worse* than `Count`. – RubberDuck Sep 05 '15 at 01:14
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In the specific case of `List`, performance is the same because the extension uses the property. True for all collections implementing the `ICollection` interface. – Thorkil Holm-Jacobsen Sep 05 '15 at 07:49
@tahatmat i believe linq will use Length for arrays as well. – Andy Sep 05 '15 at 19:51

sstan · Answer 3 · 2015-09-05T17:31:42.400

11

Actually, keep in mind that there is the List.Count property, and then there is the Enumerable.Count method.

In your example, you are using the Enumerable.Count() method, which has to iterate through every single item of the enumeration to return a result. That is clearly slower than calling Any() which only needs to iterate over the first item, if it exists.

EDIT:

In the comments it was pointed out, rightly so, that Enumerable.Count() extension method doesn't need to iterate through all the items if it detects that the enumerable also happens to be an ICollection<T>. So in the case of a List<T>, using the Count property or method doesn't actually make a difference.

IEnumerable.Count source:

public static int Count<TSource>(this IEnumerable<TSource> source) {
    if (source == null) throw Error.ArgumentNull("source");
    ICollection<TSource> collectionoft = source as ICollection<TSource>;
    if (collectionoft != null) return collectionoft.Count;
    ICollection collection = source as ICollection;
    if (collection != null) return collection.Count;
    int count = 0;
    using (IEnumerator<TSource> e = source.GetEnumerator()) {
        checked {
            while (e.MoveNext()) count++;
        }
    }
    return count;
}

edited Sep 05 '15 at 17:31

answered Sep 04 '15 at 18:28

sstan

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Fair enough. What about the use of the .Count property then? wouldn't that make the read significantly faster, maybe as fast or even faster than calling .Any() ? – Gil Sand Sep 04 '15 at 18:29
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With a `List` the performance difference will be negligible. So just use what you prefer. But for other types of IEnumerables, you only get to pick between `Count()` (the method), and `Any()`, and in that case, `Any()` will always be the clear winner for your use case and should be preferred. For what it's worth, I think `Any()` is quite readable and clear. – sstan Sep 04 '15 at 18:34
@sstan yes unless if the ienumerable can be cast to a collention then it can be optimized and it won't matter. – Esben Skov Pedersen Sep 04 '15 at 19:10
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`Count()` has the same complexity as `Count` for `ICollection`s, since the extension method then uses the property instead of iterating. – Thorkil Holm-Jacobsen Sep 05 '15 at 07:38
Linq extensions are optimised for known interfaces - IList , ICollection. Performance discussion here is totally redundant, even if that is an implementation detail – Gusdor Sep 05 '15 at 17:20
@tahatmat: Absolutely right. I had not noticed that in the implementation. Thanks for pointing that out. – sstan Sep 05 '15 at 17:24

JacquesB · Answer 4 · 2015-09-06T09:07:29.663

A surprising question - I find the intent of list.Any() to be much clearer than the intent of list.Count()!=0.

Intent means: If you read someones code (and you didn't write it yourself), is it completely obvious what the programmer wants to achieve and why it written written like it is? If a common problem is solved in a needlessly complex way, you immediately gets suspicious and wonder why the developer didn't use the simple way. You look through the code and try to see if you have missed something. You are afraid to change the code because you worry there is some side effect you are missing and changing it may cause unexpected problems.

The intent of using the Any() method is completely clear - you want to know if there are any elements in the list or not.

The intent of the expression Count()!=0 on the other hand is not obvious for the reader. It is of course not hard to see that the expression tells you if the list is empty or not. The questions arises because you write it this particular way rather than using the standard method. Why do you use Count() explicitly? If you really just need to know if there are any elements in a list, why do you want to count the whole list first? As soon as you reach 1 you already have have your answer. If the source was an iterator over a large (perhaps infinite) collection or is translated to sql, it could make a big difference performance wise. So maybe the explicit use of Count() is to force a deferred query to execute or to traverse an iterator?

But the source is actually a List<T> where Count() is O(1) and has no side effects. But if the code relies of this property of List<T>, then why not use the Count-property which more clearly indicate that you expect an O(1) operation with no side effects?

As it is written, list.Count()!=0 does exactly the same as list.Any() except it is needlessly more complex and the intent is unclear.

I read both as, "does the list contain any items?" `Count()` has an implied conversion that I would avoid using, but it's not unclear. The compiler may optimize it away, which only makes it careless coding. — Suncat2000, May 25 '17 at 14:53

score 3 · Answer 5 · answered Sep 04 '15 at 23:14

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Maybe it's just the word? Any is an adjective, not really saying anything. Coming from Java, I'd call it isNonEmpty which contains a verb. A SQL guy might prefer EXISTS. But maybe Any fits best in the C# system.

Whatever the word choice, once you get used to it, it must be way clearer. Would you ask "Is there more than zero beer bottles left". Would you expect one or more persons starting to count them before they answer "No, there isn't any"?

answered Sep 04 '15 at 23:14

maaartinus

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The name "any" makes sense when you think of it in terms of LINQ: `Any()` is really a shortcut for `Any(o => true)` – BlueRaja - Danny Pflughoeft Sep 04 '15 at 23:30
I wouldn't normally use empty to describe if an enumerable had anytjing to enumerate over. But "is there **any**thing to enumerate" seems natural to me, and Any works against any enumeration. – Andy Sep 05 '15 at 19:59

What's the use of .Any() in a C# List<>?

5 Answers5