检查值是否在数组中（C#）
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Check if a value is in an array (C#)
提问by Cecil Rodriguez
How do I check if a value is in an array in C#?
如何检查值是否在 C# 中的数组中？
Like, I want to create an array with a list of printer names.
就像，我想创建一个包含打印机名称列表的数组。
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.
这些将被提供给一个方法，该方法将依次查看每个字符串，如果字符串与数组中的值相同，则执行该操作。
For example:
例如：
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.
这些是打印机的名称，它们被提供给 PrinterSetup 方法。
PrinterSetup will look sort of like this (some pseudocode):
PrinterSetup 看起来像这样（一些伪代码）：
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?
如何if (printer == "jupiter")以 C# 可以识别的方式进行格式化？
采纳答案by Dmytro
Add necessary namespace
添加必要的命名空间
using System.Linq;
Then you can use linq Contains()method
然后你可以使用 linqContains()方法
string[] printer = {"jupiter", "neptune", "pangea", "mercury", "sonic"};
if(printer.Contains("jupiter"))
{
Process.Start("BLAH BLAH CODE TO ADD PRINTER VIA WINDOWS EXEC"");
}
回答by Dmytro
You are just missing something in your method:
你只是在你的方法中遗漏了一些东西：
public void PrinterSetup(string printer)
{
if (printer == "jupiter")
{
Process.Start("BLAH BLAH CODE TO ADD PRINTER VIA WINDOWS EXEC"");
}
}
Just add stringand you'll be fine.
只需添加string，你会没事的。
回答by code4life
Something like this?
像这样的东西？
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"");
}
}
回答by Brandon Moretz
Not very clear what your issue is, but it sounds like you want something like this:
不太清楚您的问题是什么，但听起来您想要这样的东西：
List<string> printer = new List<string>( new [] { "jupiter", "neptune", "pangea", "mercury", "sonic" } );
if( printer.Exists( p => p.Equals( "jupiter" ) ) )
{
...
}
回答by Raz Megrelidze
public static bool Contains(Array a, object val)
{
return Array.IndexOf(a, val) != -1;
}
回答by Raz Megrelidze
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);
Console.WriteLine(b);
Console.WriteLine(c);
Console.WriteLine(d);
----------------------------output-----------------------------------
1)True 2)False 3)True 4)False
1)正确 2)错误 3)正确 4)错误
回答by Guest
if ((new [] {"foo", "bar", "baaz"}).Contains("bar"))
{
}
回答by Sergey Brunov
Consider using HashSet<T>Classfor the sake of lookup performance:
为了查找性能考虑使用HashSet<T>Class：
This method is an O(1) operation.
该方法是一个 O(1) 操作。
For example:
例如：
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");
}
// ...
}
}
回答by Ricardo Fercher
I searched now over 2h to find a nicely way how to find duplicatesin a list and how to remove them. Here is the simplest answer:
我现在搜索了 2 小时以上，以找到一种很好的方法，即如何在列表中查找重复项以及如何删除它们。这是最简单的答案：
//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!
输出将如下所示： 重复元素将在名为 distinct 的新列表中删除！
回答by Philm
Note: The question is about arrays of strings. The mentioned routines are not to be mixed with the .Contains method of single strings.
注意：问题是关于字符串数组。上述例程不能与单个字符串的 .Contains 方法混合使用。
I would like to add an extending answer referring to different C# versions and because of two reasons:
我想添加一个涉及不同 C# 版本的扩展答案，原因有两个：
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).
接受的答案需要 Linq，它是完全惯用的 C#，但它并非没有成本，并且在 C# 2.0 或更低版本中不可用。当涉及数组时，性能可能很重要，因此在某些情况下您希望使用 Array 方法。
没有答案直接涉及还要求将其放入函数的问题（因为有些答案也将字符串与字符串数组混合，这并非完全不重要）。
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.
Array.Exists() 是一种 C#/.NET 2.0 方法，不需要 Linq。在数组中搜索是 O(n)。为了更快地访问，请使用 HashSet 或类似的集合。
Since .NET 3.5 there also exists a generic method Array<T>.Exists():
从 .NET 3.5 开始，还存在一个通用方法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 ".Contains" for strings for all arrays without including Linq:
您可以编写自己的扩展方法（C# 3.0 及更高版本）来添加语法糖，以便在不包括 Linq 的情况下为所有数组的字符串获得相同的“.Contains”：
// Using the generic extension method below as requested.
public void PrinterSetup(string[] printer)
{
if (printer.Contains("jupiter"))
{
Process.Start("BLAH BLAH CODE TO ADD PRINTER VIA WINDOWS EXEC");
}
}
public static bool Contains<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 Contains()method is used and not the one of Linq.
在这种情况下，使用此Contains()方法而不是 Linq 方法。
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.
其他地方提到的 .Contains 方法是指List<T>.Contains（自 C# 2.0 起）或ArrayList.Contains（自 C# 1.1 起），但不直接指代数组本身。
