How to remove elements from a generic list while iterating over it?

c#, generics, key-value, list, loops

Solution

Iterate your list in reverse with a for loop:

for (int i = safePendingList.Count - 1; i >= 0; i--)
{
    // some code
    // safePendingList.RemoveAt(i);
}

Example:

var list = new List<int>(Enumerable.Range(1, 10));
for (int i = list.Count - 1; i >= 0; i--)
{
    if (list[i] > 5)
        list.RemoveAt(i);
}
list.ForEach(i => Console.WriteLine(i));

Alternately, you can use the RemoveAll method with a predicate to test against:

safePendingList.RemoveAll(item => item.Value == someValue);

Here's a simplified example to demonstrate:

var list = new List<int>(Enumerable.Range(1, 10));
Console.WriteLine("Before:");
list.ForEach(i => Console.WriteLine(i));
list.RemoveAll(i => i > 5);
Console.WriteLine("After:");
list.ForEach(i => Console.WriteLine(i));

Problem

I am looking for a better pattern for working with a list of elements which each need processed and then depending on the outcome are removed from the list. You can't use `.Remove(element)` inside a `foreach (var element in X)` (because it results in `Collection was modified; enumeration operation may not execute.` exception)... you also can't use `for (int i = 0; i < elements.Count(); i++)` and `.RemoveAt(i)` because it disrupts your current position in the collection relative to `i`. Is there an elegant way to do this?

Original source

Related problems