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NaCl
Asked: 2020-06-29 07:18:48 +0800 CST 2020-06-29 07:18:48 +0800 CST

Why does List<T>.Remove(T) only remove the first matching element?

  • 772

I have the following problem.

I have a List<string>with information that can vary depending on the actions taken and I need to remove all the elements that match the string.

I have tried the following code in the List<T>:

List<string> Strings = new List<string>() {
    "658", "123", "321", "123"
};
foreach (string s in Strings) Console.WriteLine(s); // Imprime: 658, 123, 321, 123
Strings.Remove("123");
foreach (string s in Strings) Console.WriteLine(s); // Imprime: 658, 321, 123

And I need the last loop to foreachreturn 658, 321.

I know I can loop through the List, but I need to understand why not all matching elements are removed.

Greetings.

c#

3 Answers

  1. Best Answer

    There are several alternatives for what you are looking for, you could use

    List<string> Strings = new List<string>() {
    "658", "123", "321", "123"
};

foreach (string s in Strings) Console.WriteLine(s);
Strings.RemoveAll(x=> x=="123");
foreach (string s in Strings) Console.WriteLine(s);

    or help you with linq

    List<string> Strings = new List<string>() {
    "658", "123", "321", "123"
};

foreach (string s in Strings) Console.WriteLine(s);
Strings = Strings.Where(x=> x != "123").ToList();
foreach (string s in Strings) Console.WriteLine(s);

    with linq you basically filter by removing the value you don't want

    • 14

  2. The Removeonly removes the first element, to remove all matches you have several options:

    1. Use the RemoveAll( documentation ), specifically:

      Strings.RemoveAll(x => x == "123");

      It is important to note that he RemoveAll updates the current list.

    2. Another good option is to use Linq to do it (with Select):

      List<string> Strings2 = Strings.Select(x => x != "123"); //Sin el ToList()!

    3. Also with Linq but with where(I prefer the del option Select):

      List<string> Strings2 = Strings.Where(x => x != "123").ToList();
    • 7

  3. I'm not a C# expert but maybe you should use the RemoveAll method instead of Remove

    Console.WriteLine("\n{0} elementos quitados mediante RemoveAll(MetodoDeFiltrado()).", 
            lista.RemoveAll(MetodoDeFiltrado()));
    • 2