How to Remove Elements from a Generic List While Iterating Over It

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

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));

Python: How to remove elements from list while iterating through it without skipping future iterations

You are right. You need an additional list. But there is an easier solution.

def print_numTXTs(fileList):

    counter = 0
    for file in list(fileList):
        if file.name[-4:] == ".txt":
            counter +=1
            if file.name == "a.txt":
                fileList.remove(file)
   

The secret is "list(fileList)". You creating an additional list and iterates over this.

Just as powerful are list compressions. In your example it should work like this. I have not tried now...only quickly written here.

fileList = [ file for file in fileList if file.name != "a.txt" ]

Remove an item in a list while it's in a foreach loop c#

Try just creating another temporary list for the items that need to be deleted then when your done looping you can just delete the ones in the temp list.

List<Type> temp = new List<Type>()
foreach(item in mainList)
{
   if (item.Delete)
   {
      temp.Add(item);
   }
}

foreach (var item in temp)
{
   mainList.Remove(item);
}

Best way to iterate over a list and remove items from it?

Willy-nilly you have to loop over the list, and the for loop is the most efficient one:

  for (int i = safePendingList.Count - 1; i >= 0; --i) 
    if (condition)
      safePendingList.RemoveAt(i);

If you want to remove in range (not in the entire list), just modify for loop:

  // No Enumarable.Range(1, 10) - put them into "for"
  for (int i = Math.Min(11, safePendingList.Count - 1); i >= 1; --i)
    if (condition)
      safePendingList.RemoveAt(i); 

Or if you have to remove items in forward looping:

  for (int i = 0; i < safePendingList.Count;) // notice ++i abscence
    if (condition)
      safePendingList.RemoveAt(i);
    else
      i += 1; // ++i should be here

On the contrary safePendingList.ToList() creates a copy of initial safePendingList and this means memory and CPU overhead:

  // safePendingList.ToList() - CPU and Memory overhead (copying)
  foreach (var item in safePendingList.ToList()) {
    if (condition)
      myList.Remove(item); // Overhead: searching
  }

However, the most reasonable plan in many cases is just to let .Net work for you:

  safePendingList.RemoveAll(item => condition);

How to remove items from a list while iterating?

You can use a list comprehension to create a new list containing only the elements you don't want to remove:

somelist = [x for x in somelist if not determine(x)]

Or, by assigning to the slice somelist[:], you can mutate the existing list to contain only the items you want:

somelist[:] = [x for x in somelist if not determine(x)]

This approach could be useful if there are other references to somelist that need to reflect the changes.

Instead of a comprehension, you could also use itertools. In Python 2:

from itertools import ifilterfalse
somelist[:] = ifilterfalse(determine, somelist)

Or in Python 3:

from itertools import filterfalse
somelist[:] = filterfalse(determine, somelist)

Remove an item from a generic list while in a foreach

The simplest approach is to remember all the elements you want to remove, then remove them later:

var tilesToRemove = new List<CollisionTiles>();
foreach (var tile in map.CollisionTiles)
{
    if (!tile.IsTransparent)
    {
        player.Collision(tile.Rectangle, map.Width, map.Height);
    }
    else if (player.PickUp(tile, map.Width, map.Height))
    {
        tilesToRemove.Add(tile);
    }
    camera.Update(player.Position, map.Width, map.Height);
}

// Remove all the ones we didn't want
foreach (var tile in tilesToRemove)
{
    map.Remove(tile);
}
// Potentially call camera.Update here? We don't know if it uses the tiles

(It's not clear why you're calling camera.Update that often, by the way - could you not call it once after the loop?)

Java: How to remove elements from a list while iterating over/adding to it

Split off a method stop() from stopAndRemove(). Then write the loop with an explicit iterator, do the stop and then iterator.remove().

"and" in a method name is a code smell.

C# List - Removing items while looping / iterating

If you need to remove elements then you must iterate backwards so you can remove elements from the end of the list:

var data=new List<string>(){"One","Two","Three"};
for(int i=data.Count - 1; i > -1; i--)
{
    if(data[i]=="One")
    {
        data.RemoveAt(i);
    }
}

However, there are more efficient ways to do this with LINQ (as indicated by the other answers).

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