Check if a value is in an array (C#)

Question

How do I check if a value is in an array in C#?

Like, I want to create an array with a list of printer names.

These will be fed to a method, which will look at each string in turn, and if the string is the same as a value in an array, do that action.

For example:

string[] printer = {"jupiter", "neptune", "pangea", "mercury", "sonic"};
foreach (p in printer)
{
   PrinterSetup(p);     
}

These are the names of the printers, they are being fed to the PrinterSetup method.

PrinterSetup will look sort of like this (some pseudocode):

public void PrinterSetup(printer)
{
   if (printer == "jupiter") 
   {
      Process.Start("BLAH BLAH CODE TO ADD PRINTER VIA WINDOWS EXEC");
   }
}

How do I format if (printer == "jupiter") in a way that C# can recognize?

Solution 1

Add necessary namespace

using System.Linq;

Then you can use linq Contains() method

string[] printer = {"jupiter", "neptune", "pangea", "mercury", "sonic"};
if(printer.Contains("jupiter"))
{
    Process.Start("BLAH BLAH CODE TO ADD PRINTER VIA WINDOWS EXEC"");
}

Solution 2

Add using System.Linq; at the top of your file. Then you can do:

if ((new [] {"foo", "bar", "baaz"}).Contains("bar"))
{

}  

Solution 3

    public static bool Contains(Array a, object val)
    {
        return Array.IndexOf(a, val) != -1;
    }

Solution 4

Something like this?

string[] printer = {"jupiter", "neptune", "pangea", "mercury", "sonic"};
PrinterSetup(printer);

// redefine PrinterSetup this way:
public void PrinterSetup(string[] printer)
{
    foreach (p in printer.Where(c => c == "jupiter"))
    {
        Process.Start("BLAH BLAH CODE TO ADD PRINTER VIA WINDOWS EXEC"");
    }
}

Solution 5

Note: The question is about arrays of strings. The mentioned routines are not to be mixed with the .Contains method of single strings.

I would like to add an extending answer referring to different C# versions and because of two reasons:

• The accepted answer requires Linq which is perfectly idiomatic C# while it does not come without costs, and is not available in C# 2.0 or below. When an array is involved, performance may matter, so there are situations where you want to stay with Array methods.

• No answer directly attends to the question where it was asked also to put this in a function (As some answers are also mixing strings with arrays of strings, this is not completely unimportant).

Array.Exists() is a C#/.NET 2.0 method and needs no Linq. Searching in arrays is O(n). For even faster access use HashSet or similar collections.

Since .NET 3.5 there also exists a generic method Array<T>.Exists() :

public void PrinterSetup(string[] printer)
{
   if (Array.Exists(printer, x => x == "jupiter"))
   {
      Process.Start("BLAH BLAH CODE TO ADD PRINTER VIA WINDOWS EXEC");
   }
}

You could write an own extension method (C# 3.0 and above) to add the syntactic sugar to get the same/similar ".Contains" as for strings for all arrays without including Linq:

// Using the generic extension method below as requested.
public void PrinterSetup(string[] printer)
{
   if (printer.ArrayContains("jupiter"))
   {
      Process.Start("BLAH BLAH CODE TO ADD PRINTER VIA WINDOWS EXEC");
   }
}

public static bool ArrayContains<T>(this T[] thisArray, T searchElement)
{
   // If you want this to find "null" values, you could change the code here
   return Array.Exists<T>(thisArray, x => x.Equals(searchElement));
}

In this case this ArrayContains() method is used and not the Contains method of Linq.

The elsewhere mentioned .Contains methods refer to List<T>.Contains (since C# 2.0) or ArrayList.Contains (since C# 1.1), but not to arrays itself directly.

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Comments

[Jon Skeet]

Try giving your parameter name a type (string) and it will be fine.

[newfurniturey]

I'm kind of confused as the question. Are you asking how to check if a value is in an array, or how to do string-comparison in C#? If it's the latter, you would use printer.Equals("jupiter"). If it's the former, use linq and printer.Contains("jupiter")

[kaz]

This is a general example - can you provide one that matches the question better?

[Jeppe Stig Nielsen]

I like this. However, it will fail if a is a multidimensional array (such as new string[10, 20, 15] for example), with an exception. It will also fail with one-dimensional arrays that are not indexed from zero (such as Array.CreateInstance(typeof(string), new[] { 5, }, new[] { -2, }), rare in C# I admit), with a possibly wrong return value. These shortcomings are easy to fix with generics: public static bool Contains<TElement>(TElement[] a, TElement val) { return Array.IndexOf(a, val) != -1; }

[Grant Birchmeier]

It may be a general example, but it's exactly what I was looking for.

[peter.cyc]

I suggest to change name to ArrayContains() to avoid confusion with the Linq Contains()

[Philm]

I´ve done this, although there are also arguments against: It is the basic idea of polymorphism to use the same name for different data types, Especially with a Linq-setting in mind. Using different names is not polymorph. But readibility and avoiding misunderstandings shall win, I think, so, yes.