Question

I have a list of items e.g

id
1
2
3
4
5
6
7
8
9
10
11
12
13

I want to write this to csv and do it in batches of 5 so when it reaches id 5 it will go to next batch. I was thinking of doing mod to cater for this so

int noOfIds = MyIDList.Count % 5; // to get the number of loops i need

List<MyIDList> topFiveID = (from c in MyIDList
                select c).Take(5).ToList(); // get top 5 from the list

Then I am getting the rest by

List<MyIDList> restOfIDs = MyIDList.Where(c => !topFiveID.Any(tc => tc.ID == c.ID)).ToList();

Now I can see this can cater for up to 9 ids, can someone please tell me how to cater for all the ids no matter how many are there.

Hope it is clear enough.

Answer 1

The following will return batches of a given size from an enumeration:

public static IEnumerable<IEnumerable<TSource>> Batch<TSource>(
    this IEnumerable<TSource> source,
    int batchSize)
{
    var batch = new List<TSource>();
    foreach (var item in source)
    {
        batch.Add(item);
        if (batch.Count == batchSize)
        {
             yield return batch;
             batch = new List<TSource>();
        }
    }

    if (batch.Any()) yield return batch;
}

Used like:

foreach (var list in MyIdList.Batch(5))
{
    // list is an IEnumerable<T> containing up to 5 items
    Console.WriteLine("{0}", String.Join(",", list));
}