How to combine || operators in condition statement

Question

Instead of

if (foo == "1" || foo == "5" || foo == "9" ... )

I like to combine them similar to the following (which doesn't work):

if (foo == ("1" || "5" || "9" ... ))

Is that possible?

Just as a related aside, Perl 6 is supposed to have these (`if (foo == any(1, 5, 9))`), and Perl 5 code can use them too using CPAN modules http://search.cpan.org/perldoc?Quantum%3A%3ASuperpositions or http://search.cpan.org/perldoc?Perl6%3A%3AJunction This any() and all() functions are called 'junctions', and I love the idea :) — Sundar R, Jul 23 '13 at 21:09
Do yuo have dicts in `c#`, we have in Python so we can do: `{"1": 1, "5": 1, "9": 1, .... }.gets(foo, false);` its `O(1)`. --- `gets()` is a dict's function that index `foo` key in dict and give value, else second arguments=false as default. .. I am not a c# user I came from hot question. — Grijesh Chauhan, Jul 23 '13 at 21:28
Another side note, python uses `foo in ("1", "5", "9")` which I think is less ambigous. If c# has a terse literal array syntax, perhaps the analogue would be `["1", "5", "9"].index(foo) != -1` — tobyodavies, Jul 23 '13 at 22:47
Won't work in all situations, so I won't post this as an answer, but for your specific example: `if (int.Parse(foo) % 4 == 1)` will do the trick as a good simple one-liner. Assumes in this case that `foo` will always be a single-digit parse-able int. Not knowing your intended use case I can't tell if that's what you'd need. — Darrel Hoffman, Jul 24 '13 at 03:05
Yeah, I was [thinking][1] it was an annoyance, too.... [1]: http://programmers.stackexchange.com/questions/205165/operator-distributivity-in-expressions-syntactic-sugar — Michael Rosefield, Jul 24 '13 at 08:12
in PERL you don't really need any function, you can just do a regex `if(foo=~/^(1|5|9)$/)` — Naryl, Jul 24 '13 at 09:55
Since we're mentioning different languages, Ruby does this easily: `["1", "5", "9"].include? foo`. Or Haskell: `any (== foo) ["1", "5", "9"]`. — Malcolm, Jul 24 '13 at 10:51
@sundar: Perl can also do `if ( grep { $foo eq $_ } (1, 5, 9) ) ...`. The resulting array evaluated as a scalar will evaluate 0 if empty (i.e., nothing matched) or the size of the array. — Blrfl, Jul 24 '13 at 12:26
Similar: http://stackoverflow.com/questions/17378673/1075247 — AncientSwordRage, Jul 24 '13 at 13:00
@Mohit That's why I used `int.Parse`. It would work for this very specific scenario, but if you passed in a string that wasn't parse-able as an int, it'd fail. (You could use `int.TryParse`, but it requires an extra line for validation.) Like I said, won't work in every case, but if you know certain things ahead of time it does. — Darrel Hoffman, Jul 24 '13 at 14:55
@GrijeshChauhan: if you don't need the values, then using `set()` is generally going to be better than a `dict()` whose values are always 1. — Lie Ryan, Jul 24 '13 at 15:08
@DarrelHoffman is tryParse available for lower versions like 3.5 — Trikaldarshiii, Jul 24 '13 at 17:23
@Mohit Pretty sure TryParse has always been available - at least as early as 2.0, which is the earliest that still seems to be covered on http://msdn.microsoft.com/en-us/library/system.int32.tryparse%28v=vs.80%29.aspx — Darrel Hoffman, Jul 24 '13 at 17:30
@DarrelHoffman ya i think i mixed with TryParse of Enum which is now available from 4.0 but not earlier it my lack — Trikaldarshiii, Jul 24 '13 at 19:11
@DarrelHoffman check my answer i think i have ultimate solution — Trikaldarshiii, Jul 24 '13 at 19:42

Trevor Pilley · Accepted Answer · 2013-07-23T17:33:47.867

169

Unfortunately not, your best bet is to create an extension method

public static bool IsOneOf<T>(this T value, params T[] options)
{
    return options.Contains(value);
}

and you can use it like this:

if (foo.IsOneOf("1", "5", "9"))
{
    ...
}

Being generic, it can be used for any type (int, string etc).

edited Jul 23 '13 at 17:33

answered Jul 23 '13 at 16:27

Trevor Pilley

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If I had any more up votes for the day I'd give you a +1 friend. Good, clever solution. – Mike Perrenoud Jul 23 '13 at 16:37
6

It's the cleanest and most reusable of out all answers. – Zbigniew Jul 23 '13 at 16:38
1

This and more http://stackoverflow.com/questions/271398/what-are-your-favorite-extension-methods-for-c-codeplex-com-extensionoverflow – Tomasito Jul 23 '13 at 23:45
1

The || operator in OP's question is a short cut operator. Does the Contains extension method exit as soon as it finds a match? Or does it iterate through the whole array? If it does not, this is preferable to the switch..case because you can use non-constant expressions. – Boluc Papuccuoglu Jul 24 '13 at 10:23
I would assume that Array.Contains would return true as soon as it finds a match in the collection it would make sense that it did but you'd have to decompile the source of mscorlib to verify that. – Trevor Pilley Jul 24 '13 at 10:27
@TrevorPilley Not necessarily. Make arrays of many sizes starting with `1` and call Contains for `1`. If the call is O(1), then it stops when it finds a match. If it is O(N), then it checks the whole array. No need for decompilation. – luiscubal Jul 24 '13 at 14:12
I use this exact code, but I call my method "In" because the usage is very similar to SQL. – KeithS Jul 24 '13 at 14:56
1

Unless optimized at compile time (such as is possible if all the values are constants), creating the `params T[]` array is always going to be `O(N)` so it will not necessarily benefit from short-circuit. – Lie Ryan Jul 24 '13 at 15:11
You should name the method `IsAnyOf`. The terms `Any` and `All` are used in the .NET framework for similar situations, so the terms are familiar and prevent the user from ever wondering whether `IsOneOf` means `IsAnyOf` or `IsOnlyOneOf`. – Sam Harwell Jul 25 '13 at 02:51
Adding a null source check to the extension method would be good practice, as well. Could potentially save you from digging through some cryptic stack traces. – nw. Aug 06 '13 at 23:14

score 37 · Answer 2 · answered Jul 23 '13 at 16:25

37

You cannot do it this way. Instead you can do this:

string[] validValues = new string[] { "1", "5", "9", "whatever" };
if(validValues.Contains(foo))
{
    // do something
}

answered Jul 23 '13 at 16:25

Zbigniew

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I'm not sure, but it appears somebody went through and down voted everybody's except for @Gray. – Mike Perrenoud Jul 23 '13 at 16:30
:( Wasn't me, I promise. I shall go and upvote all. – Gray Jul 23 '13 at 16:31
Then, as it appears, someone came in, and downvoted all (before Gray posted answer). Well, it's not the first time... – Zbigniew Jul 23 '13 at 16:34
2

not me, and I don't understand why my question was downvoted twice either.. – KMC Jul 23 '13 at 17:04
5

Some (not me!) might consider it basic or something that could have been answered by Google or elsewhere on the site. Or someone might just be a jerk. Or both. I gave you an upvote to undo the damage. Take that, anonymous jerk! – thumbtackthief Jul 23 '13 at 20:48
Unfortunately you just have to put up with a few idiotic jerks. The plus votes you are getting from people fed up with them should hopefully make up for it though! (+1) – Relaxing In Cyprus Jul 24 '13 at 08:26
Well, I certainly wasn't expecting to get +24 for this answer, it's accually pretty simple. On the other hand all my most upvoted answers are pretty much basic. Thanks! – Zbigniew Jul 24 '13 at 15:09

Mike Perrenoud · Answer 3 · 2013-07-24T15:12:21.427

25

One possible option is this:

switch (foo)
{
    case "1":
    case "5":
    case "9":
        // your code here

        break;
}

Another possible option is this:

var vals = new string[] { "1", "5", "9" };
if (vals.Contains(foo))
{
    // your code here
}

edited Jul 24 '13 at 15:12

answered Jul 23 '13 at 16:25

Mike Perrenoud

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i think its more code that foo = 1 || foo = 2 ....... – Trikaldarshiii Jul 24 '13 at 19:12
@mohit, the second option wouldn't be because you'd only have to declare the array once in the class. But yeah, I've been waiting on this syntax enhancement for a decade now. – Mike Perrenoud Jul 24 '13 at 19:21
would you like to consider to see my way dont you think its pretty better than the any answer given – Trikaldarshiii Jul 24 '13 at 19:41

score 23 · Answer 4 · answered Jul 23 '13 at 16:31

23

If all options are just one character you could do:

if ("159".IndexOf(foo) != -1)
{
  //do something
}

answered Jul 23 '13 at 16:31

jsedano

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1

Hmm, interesting approach. One I've never considered. Nice. – Mike Perrenoud Jul 23 '13 at 16:38
13

And there goes the readability... – RedX Jul 24 '13 at 08:11
4

@user902383 Yes I know that, that's why I wrote: **If all options are just one character** on the top of my answer – jsedano Jul 24 '13 at 14:01
@RedX I'm all about readability, that's why I think Trevor Pilley answer is the best one, this is great **foo.IsOneOf("1", "5", "9")**, I think my answer /could/ hurt readability depending on the context. – jsedano Jul 24 '13 at 18:50

Gray · Answer 5 · 2013-07-24T13:35:23.593

18

Here is yet another alternative:

bool x = new[] { "1", "5", "9" }.Any(a => a == "5"); //x == true
bool y = new[] { "1", "5", "9" }.Any(a => a == "8"); //y == false

It is better to use .Contains(foo) in this case, as the flexibility of the lambda is rather wasted here. If there was a complex expression that needed to be done, Any would be more useful.

edited Jul 24 '13 at 13:35

answered Jul 23 '13 at 16:28

Gray

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Instead of `.Any(x => x == val)` I would rather use `.Contains(val)`. – fjdumont Jul 24 '13 at 10:31
I could see that. I think, for this kind of collection, it makes no difference (aside from syntax), but for certain collections, like say, a Binary Search Tree, `.Contains` would perform a binary search... where `.Any` would still go through in O(n). – Gray Jul 24 '13 at 12:29
... which would be awesome, right? A binary search tree searches in O(log n) IIRC. – fjdumont Jul 24 '13 at 13:20
Right, that's what I was saying. This was a helpful discussion, though. I learned the real reason to use Any over Contains. You would only really use Any() over Contains if you need a specialized lamda (which I do not have in this case). Contains() is better (worst case: the same) as Any unless you need to check something a little more complex than if the value is equal. I'll leave my answer here just as a reference for future people. – Gray Jul 24 '13 at 13:29

score 13 · Answer 6 · answered Jul 23 '13 at 16:25

13

You can do this, if that's acceptable to you:

if ( (new string[] {"1","9","5","6" }).Contains(foo))
{

}

answered Jul 23 '13 at 16:25

Icarus

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Does this allocate a new array every time it runs? – Samuel Edwin Ward Jul 23 '13 at 20:39
@SamuelEdwinWard: It looks like it should. I don't know if the current runtime does it but escape analysis on this line should allow it to instantly free the new array. – Zan Lynx Jul 23 '13 at 23:42
1

You can leave out `string`, the compiler will infer this automatically from the specified array values. – Sandor Drieënhuizen Jul 24 '13 at 11:35
2

@SamuelEdwinWard - yes it will allocate and populate a new array each time the code block is executed. If the list of allowed values is defined at compile time & essentially "static" for the lifetime of the application, you could define it as a const or static field which would reduce the GC overhead of the method if it is called frequently. – Trevor Pilley Jul 24 '13 at 13:43

score 9 · Answer 7 · answered Jul 23 '13 at 16:25

9

You may use the switch statement:

switch (foo) {
    case "1":
    case "5":
    case "9":
        // ...
        break;
    case "2":
    case "4":
        // ...
        break;
}

If foo is a string, pay attention on case sensitivity.

answered Jul 23 '13 at 16:25

joe

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score 9 · Answer 8 · answered Jul 23 '13 at 16:31

If you have multiple if conditions you should always consider using switch statements as compiler will create Jumptables whereever possible to increase speed. You should take a look here for speed test. Thing to note here is that if number of conditions is big enough to cover overheads, C# compiler will also create a HashTable object.

So this is a better approach,

switch (foo) {
case "1":
case "5":
case "9":
    // ...
    break;
case "2":
case "4":
    // ...
    break;
}

How to combine || operators in condition statement

8 Answers8

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