Is there set comparsion operation for C#?

Question

I have the following while statement:

while ((leftSide.Count-rightSide.Count!=-1)&&(leftSide.Count-rightSide.Count!= 0))
{
     // Do stuff here
}

I would love to write this something like this:

while (leftSide.Count - rightSide.Count ! in [-1, 0])
{
     // Do stuff here
}

but that is illegal syntax. I am wondering, is there some way to that? Some syntax I don't know?

I want to see if the difference of the counts in a set of numbers without having to re-include the whole left side of the statement again?

I suppose I could do this:

int x = leftSide.Count-rightSide.Count;
while ((x != -1) && (x != 0))
{
     // Do stuff here
     x = leftSide.Count-rightSide.Count;
}

but I would rather not.

If there is no way to do a "set" comparison does anyone know why? C# is such a full featured language that it seems odd to have something like this missing.

See: http://stackoverflow.com/questions/973916/linq-where-in-collection-clause — Mike Atlas, Feb 25 '11 at 16:37

score 8 · Accepted Answer · answered Feb 25 '11 at 16:34

8

Using extension methods, you could easily create an In operator:

public static class Extensions
{
    public static Boolean In<T>(this T obj, params T[] items)
    {
        return items.Contains(obj);
    }
}

Usage:

Int32 i = 10;
i.In(10, 20, 30); // True

answered Feb 25 '11 at 16:34

decyclone

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Very very nice! Using the `params` makes it really usable. – Vaccano Feb 25 '11 at 17:30
Added that to my extension methods class and now my `while` looks like this: – Vaccano Feb 25 '11 at 17:31
I wrote about this in my blog. http://www.thecodepage.com/post.aspx?id=28197601-0cae-48a2-aadf-992e073f8690 – Gabriel McAdams Nov 21 '11 at 02:46

score 7 · Answer 2 · answered Feb 25 '11 at 16:33

7

It doesn't need to be in the language, because it can easily be in a library:

private static readonly int[] ValidValues = { -1, 0 };

...

if (!ValidValues.Contains(leftSide.Count - rightSide.Count))
{
    ...
}

I've used an array here because it's so small... but you would want to consider using a HashSet<int> for a large collection.

answered Feb 25 '11 at 16:33

Jon Skeet

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Once again, you are the king of the quick-draw. Well played Mr. Skeet, well played. – Justin Niessner Feb 25 '11 at 16:36
OK, I can use that. I come from a Delphi background where this was part of the language. I guess I just assumed it should be a language level feature in C# too. – Vaccano Feb 25 '11 at 16:43

score 1 · Answer 3 · answered Feb 25 '11 at 16:34

1

new[]{0,1}.Contains(leftSide.Count - rightSide.Count)

answered Feb 25 '11 at 16:34

Bala R

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This is probably the best C# way to do it. I went with the extension method because it reads a bit better to me. (With my delphi background) – Vaccano Feb 25 '11 at 17:42

score 0 · Answer 4 · answered Feb 25 '11 at 16:33

0

.Contains

http://msdn.microsoft.com/en-us/library/bhkz42b3.aspx

answered Feb 25 '11 at 16:33

Kris Ivanov

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score 0 · Answer 5 · answered Feb 25 '11 at 16:33

0

You can use HashSet (or anything implementing ISet) to do set comparisons. For your purposes, this is overkill.

I suspect that using x>0 would work for your example though.

answered Feb 25 '11 at 16:33

Jamie Treworgy

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score 0 · Answer 6 · answered Feb 25 '11 at 16:33

0

For larger amounts, you can declare a List<T> and use the Contains method:

List<int> values = new List<int> {-1, 0};

if(!values.Contains(x))
  //do stuff

answered Feb 25 '11 at 16:33

Femaref

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score 0 · Answer 7 · answered Feb 25 '11 at 16:33

0

Use extension methods:

public static class DoubleInExtension
{
    public static bool IsIn(this double x, double a, double b)
    {
        return x >= a && x <= b;
    }
}

answered Feb 25 '11 at 16:33

Aliostad

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score 0 · Answer 8 · answered Feb 25 '11 at 16:38

0

int[] set = {-1, 0};
while (!set.Contains(leftSide.Count - rightSide.Count))
{
//Do stuff here
}

answered Feb 25 '11 at 16:38

Peter Olson

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Is there set comparsion operation for C#?

8 Answers8