Question

I am dealing with trying to chunk up items in a custom collection class that implements IEnumerable (and ICollection) in C# 2.0. Let’s say, for example, that I only want 1000 items at a time and I have 3005 items in my collection. I’ve got a working solution that I demonstrate below, but it seems so primitive that I figure there has to be a better way to do this.

Here’s what I have (for example’s sake, I’m using C# 3.0’s Enumerable and var, just replace those references with a custom class in your mind):

var items = Enumerable.Range(0, 3005).ToList();
int count = items.Count();
int currentCount = 0, limit = 0, iteration = 1;

List<int> temp = new List<int>();

while (currentCount < count)
{
    limit = count - currentCount;

    if (limit > 1000)
    {
        limit = 1000 * iteration;
    }
    else
    {
        limit += 1000 * (iteration - 1);
    }
    for (int i = currentCount; i < limit; i++)
    {
        temp.Add(items[i]);
    }

    //do something with temp

    currentCount += temp.Count;
    iteration++;
    temp.Clear();
}

Can anyone suggest a more elegant way of doing this in C# 2.0? I know if this project was from the past 5 years I could use Linq (as demonstrated here and here). I know my method will work, but I’d rather not have my name associated with such ugly (in my opinion) code.

Thanks.

Answer 1

Firstly . yield is your friend here, and it was introduced with 2.0. Consider:

public static IEnumerable<List<T>> Chunk<T>(IEnumerable<T> source, int chunkSize)
{
  List<T> list = new List<T>(chunkSize);
  foreach(T item in source)
  {
    list.Add(item);
    if(list.Count == chunkSize)
    {
      yield return list;
      list = new List<T>(chunkSize);
    }
  }
  //don't forget the last one!
  if(list.Count != 0)
    yield return list;
}

Then we’re flexible in type and size, so it’s nicely reusable. The only that being restricted to 2.0 means, is that we can’t make it an extension method.