Linq Select 5 items per Iteration [duplicate]

Answer 1

Try this one:

 for (int i = 0; i < list.Count; i = i + 5) {
                var fiveitems = list.Skip(i).Take(5);
                foreach(var item in fiveitems)
                {

                }
            }

Answer 2

You can also do this with pure linq by taking advantage of integer arithmetic and the GroupBy method:

int blockSize = 5;
var group = theList.Select((x, index) => new { x, index })
                   .GroupBy(x => x.index / blockSize, y => y.x);

foreach (var block in group)
{
    // "block" will be an instance of IEnumerable<T>
    ...
}

There are a number of advantages to this approach which aren't necessarily immediately apparent:

• Execution is deferred, so it's efficient when you're working with conditional processing
• You don't need to know the length of the collection, thus avoiding multiple enumeration while also being generally cleaner than other approaches

Answer 3

It sounds like you want the Batch operator from MoreLINQ:

foreach (var batch in query.Batch(5))
{
    foreach (var item in batch)
    {
        ...
    } 
}

Answer 4

for (int i=0; i < 20 ; i++)
{
    var fiveitems = theList.Skip(i*5).Take(5);
}

Answer 5

The following static extension method would make it a straightforward process to break up a list into multiple lists of a specific batch size.

    public static IEnumerable<IEnumerable<T>> Batch<T>(this IEnumerable<T> items, int noOfItemsPerBatch)
    {
        decimal iterations = items.Count() / noOfItemsPerBatch;

        var roundedIterations = (int)Math.Ceiling(iterations);

        var batches = new List<IEnumerable<T>>();

        for (int i = 0; i < roundedIterations; i++)
        {
            var newBatch = items.Skip(i * noOfItemsPerBatch).Take(noOfItemsPerBatch).ToArray();
            batches.Add(newBatch);
        }

        return batches;
    }

Example of use

var items = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

var batchedItems = items.Batch(4);

Assert.AreEqual(batchedItems.Count() == 3);
Assert.AreEqual(batchedItems[0].Count() == 4);
Assert.AreEqual(batchedItems[1].Count() == 4);
Assert.AreEqual(batchedItems[2].Count() == 2);