How do you implement the equivalent of SQL IN() using .net

Question

In .net (c# or vb) expressions, how would you implement SQL\'s handy IN() functionality?

i.e. value in (1, 2, 4, 7)

rather than:

value = 1 or value =

Answer 1

Or using System.Linq...

(VB.NET)

Enumerable.Contains({1, 2, 4, 7}, value)

or

{1, 2, 4, 7}.Contains(value)

(C#)

Enumerable.Contains(new int[]{1, 2, 4, 7}, value);

or

new int[] {1, 2, 4, 7}.Contains(value);

Answer 2

if((new int[] {1, 2, 4, 7}).Contains(value))
{
    // Do some work.
}

As others have pointed out, you could create an In() Extension method (I'll keep it generic so you can use it on any type):

public static bool In<T>(T this obj, IEnumerable<T> col)
{
    return col.Contains(obj);
}

So the initial example becomes:

if(value.In(new int[] {1, 2, 4, 7}))
{
    // Do some work.
}

Answer 3

using System;
using System.Linq;

static class SqlStyleExtensions
{
    public static bool In(this string me, params string[] set)
    {
       return set.Contains(me);
    }
}

Usage:

if (Variable.In("AC", "BC", "EA"))
{

} 

Answer 4

I have made an extension method for this that I find quite useful. However, it is not much more than syntactic sugar wrapping the existing IEnumerable.Contains() function.

/// <summary>
/// Returns true if the value is represented in the provided enumeration.
/// </summary>
/// <typeparam name="T">Type of the value</typeparam>
/// <param name="obj">The object to check if the enumeration contains</param>
/// <param name="values">The enumeration that might contain the object</param>
/// <returns>True if the object exists in the enumeration</returns>
public static bool In<T>(this T obj, IEnumerable<T> values) {
    return values.Contains(obj);
}

Edit: Someone beat me to it, damnit. I'll keep by post here though since it's a more generic version.

Answer 5

If you will do many lookups on the same dataset it is good from a performance perspective to use HashSet<T>.

HashSet<int> numbers = new HashSet<int> { 1, 2, 4, 7 };
bool is5inSet = numbers.Contains(5);

Answer 6

Using LINQ

var q = from x in collection
        where (new int[] { 1, 2, 4, 7}).Contains(x.value)
        select x