Question

I’ve a C# generics list collection of customer Ids[customerIdsList].Lets say its count is 25.

I need to pass these Ids in sets of 10[a value which would be configurable and read from app.config]
to another method ProcessCustomerIds() which would process this customer Ids one by one.
ie. the first iteration will pass 10,next will pass the next 10 customer Ids and the last one will pass 5 Ids…and so on and so forth…

How do I achieve this using Linq?
Shall I be using Math.DivRem to do this?

int result=0;
int quotient = Math.DivRem(customerIdsList.Count, 10, out result)
Output:
quotient=2
result=5

So, I will iterate customerIdsList 2 times and invoke ProcessCustomerIds() in each step.

And if result value is greater than 0,then I will do customerIdsList.Skip(25-result) to get the last 5 customerIds from the collection.
Is there any other cleaner, more efficient way to do this? Please advise.

Answer 1

In our project, we have an extension method “Slice” which does exactly what you ask. It looks like this:

public static IEnumerable<IEnumerable<T>> Slice<T>(this IEnumerable<T> list, int size)
{
    var slice = new List<T>();
    foreach (T item in list)
    {
        slice.Add(item);
        if (slice.Count >= size)
        {
            yield return slice;
            slice = new List<T>();
        }
    }

    if (slice.Count > 0) yield return slice;
}

You use it like this:

customerIdsList.Slice(10).ToList().ForEach(ProcessCustomerIds);

An important feature of this implementation is that it supports deferred execution. (Contrary to an approach using GroupBy). Granted, this doesn’t matter most of the time, but sometimes it does.