How can I make my own "foreach" or similar for my 2D array of custom objects?

Question

I have a class (Biome) which contains a 2D array of custom objects (Level). I frequently want to loop through all (or some) of the levels and perform some actions, e.g. set their colour property.

Rather than writing the same nested for-loop over and over again, can I make my own method which will let me do something like: ForEachLevel(SetColour())?. Where SetColour() would be a method in my Biome class which just sets the Level's colour property to some random value or using some other logic based on factors within the Biome?

So instead of:

for (int r = 0; d < Rows; r++)
{
    for (int c = 0; l < Cols; c++)
    {
        if (some logic here)
            Levels[r, c].Colour = Color.Red;
        else
            Levels[r, c].Colour = Color.Green;
    }
}

I could do something like:

ForEachLevel(SetColour(--what goes here?--));

void SetColour(Level level){
    if (some logic here)
        level.Colour = Color.Red;
    else
        level.Colour = Color.Green;
}

Or even better, I'd like to make something similar which only runs a function on, say, rows X through to Y.

As you can see from my example I don't even know how I'd get the context of each Level instance into the SetColour function.

I can keep copy/pasting my custom nested for-loops to achieve what I want, but I was hoping someone with more experience might be able to understand what I'm trying to do and point me to the right direction on how I can use better C# techniques.

Because I've been vague I understand if a specific answer cannot be given, but some key concepts for further research would be appreciated!! Thanks

EDIT2 actually that previous attempt doesnt work at all. I forgot I need to actually call ForEachLevel somewhere else. Still working on it.

private void SomeOtherMethod()
{
    // where I want to actually use the ForEachLevel()
    ForEachLevel(SetLevelColor(--Level??--, Color.red));
}
private void ForEachLevel(Action DoAThing)
{
    for (int d = 0; d < Depths; d++)
    {
        for (int l = 0; l < Lanes; l++)
        {
            DoAThing();
        }
    }
}
private void SetLevelColor(Level level, Color color)
{
    // trivial example
    level.Color = color;
}

Answer 1

The LINQ methods you are referring to (e.g. .Where()) and the built-in foreach keyword both rely on a generic interface in C# called IEnumerable<T>. This is what allows you to "iterate" over a collection.

You can add this iteration behavior to your own class by having it implement the interface.

public class Level { }
public class Biome : IEnumerable<Level>
{
    private List<List<Level>> _levels = new();

    public IEnumerator<Level> GetEnumerator()
        => ForEachLevelInternal().GetEnumerator();

    IEnumerator IEnumerable.GetEnumerator()
        => GetEnumerator();

    private IEnumerable<Level> ForEachLevelInternal()
        => _levels.SelectMany(levelList => levelList);
}

If you want to then add additional LINQ-like methods to create collections over particular rows or columns, you can do so by writing a generator method.

public IEnumerable<Level> ForEachAtColumn(int index)
{
    foreach (var lst in _levels)
    {
        if (lst.Count <= 0 || index >= lst.Count) yield break;
        yield return lst[index];
    }
}

public IEnumerable<Level> ForEachAtRow(int index)
    => _levels?[index] ?? Enumerable.Empty<Level>();

If you then wanted to call a function on each element within the sequence, you can write a method for that which accepts an Action<Level> as an argument and invokes it within the loop.

public void ForEachAtColumn(int index, Action<Level> action)
{
    foreach (var level in ForEachAtColumn(index))
    {
        action(level);
    }
}

You can construct much more advanced and abstracted helper methods if you further explore the LINQ libraries (including the NuGet package System.Linq.Async).