检查值是否在数组中（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?

Answer 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"");
}

Answer 2

string[] array = { "cat", "dot", "perls" };

// Use Array.Exists in different ways.
bool a = Array.Exists(array, element => element == "perls");
bool b = Array.Exists(array, element => element == "python");
bool c = Array.Exists(array, element => element.StartsWith("d"));
bool d = Array.Exists(array, element => element.StartsWith("x"));

// Display bools.
Console.WriteLine(a); // true
Console.WriteLine(b); // false
Console.WriteLine(c); // true
Console.WriteLine(d); // false

Answer 3

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

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

}  

Answer 4

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

Answer 5

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"");
    }
}

Answer 6

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.

Answer 7

You are just missing something in your method:

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

Just add string and you'll be fine.

Answer 8

Not very clear what your issue is, but it sounds like you want something like this:

    List<string> printer = new List<string>( new [] { "jupiter", "neptune", "pangea", "mercury", "sonic" } );

    if( printer.Exists( p => p.Equals( "jupiter" ) ) )
    {
        ...
    }

Answer 9

Consider using HashSet<T> Class for the sake of lookup performance:

This method is an O(1) operation.

— HashSet<T>.Contains Method (T), MSDN .

For example:

class PrinterInstaller
{
    private static readonly HashSet<string> PrinterNames = new HashSet<string>
        {
            "jupiter", "neptune", "pangea", "mercury", "sonic"
        };

    public void Setup(string printerName)
    {
        if (!PrinterNames.Contains(printerName))
        {
            throw new ArgumentException("Unknown printer name", "printerName");
        }
        // ...
    }
}

Answer 10

I searched now over 2h to find a nicely way how to find duplicates in a list and how to remove them . Here is the simplest answer:

//Copy the string array with the filtered data of the analytics db into an list
// a list should be easier to use
List<string> list_filtered_data = new List<string>(analytics_db_filtered_data);

// Get distinct elements and convert into a list again.
List<string> distinct = list_filtered_data.Distinct().ToList();

The Output will look like this: Duplicated Elements will be removed in the new list called distinct!