Best way to remove items from a collection

Question

What is the best way to approach removing items from a collection in C#, once the item is known, but not it\'s index. This is one way to do it, but it seems inelegant at be

Answer 1

Here is a pretty good way to do it

http://support.microsoft.com/kb/555972

        System.Collections.ArrayList arr = new System.Collections.ArrayList();
        arr.Add("1");
        arr.Add("2");
        arr.Add("3");

        /*This throws an exception
        foreach (string s in arr)
        {
            arr.Remove(s);
        }
        */

        //where as this works correctly
        Console.WriteLine(arr.Count);
        foreach (string s in new System.Collections.ArrayList(arr)) 
        {
            arr.Remove(s);
        }
        Console.WriteLine(arr.Count);
        Console.ReadKey();

Answer 2

There is another approach you can take depending on how you're using your collection. If you're downloading the assignments one time (e.g., when the app runs), you could translate the collection on the fly into a hashtable where:

shortname => SPRoleAssignment

If you do this, then when you want to remove an item by short name, all you need to do is remove the item from the hashtable by key.

Unfortunately, if you're loading these SPRoleAssignments a lot, that obviously isn't going to be any more cost efficient in terms of time. The suggestions other people made about using Linq would be good if you're using a new version of the .NET Framework, but otherwise, you'll have to stick to the method you're using.

Answer 3

A lot of good responses here; I especially like the lambda expressions...very clean. I was remiss, however, in not specifying the type of Collection. This is a SPRoleAssignmentCollection (from MOSS) that only has Remove(int) and Remove(SPPrincipal), not the handy RemoveAll(). So, I have settled on this, unless there is a better suggestion.

foreach (SPRoleAssignment spAssignment in workspace.RoleAssignments)
{
    if (spAssignment.Member.Name != shortName) continue;
    workspace.RoleAssignments.Remove((SPPrincipal)spAssignment.Member);
    break;
}