Split List into Sublists with LINQ

Question

Is there any way I can separate a List<SomeObject> into several separate lists of SomeObject, using the item index as the delimiter of each split?

Let me exemplify:

I have a List<SomeObject> and I need a List<List<SomeObject>> or List<SomeObject>[], so that each of these resulting lists will contain a group of 3 items of the original list (sequentially).

eg.:

• Original List: [a, g, e, w, p, s, q, f, x, y, i, m, c]

• Resulting lists: [a, g, e], [w, p, s], [q, f, x], [y, i, m], [c]

I'd also need the resulting lists size to be a parameter of this function.

Answer 1

I find this little snippet does the job quite nicely.

public static IEnumerable<List<T>> Chunked<T>(this List<T> source, int chunkSize)
{
    var offset = 0;

    while (offset < source.Count)
    {
        yield return source.GetRange(offset, Math.Min(source.Count - offset, chunkSize));
        offset += chunkSize;
    }
}

Answer 2

Here's a list splitting routine I wrote a couple months ago:

public static List<List<T>> Chunk<T>(
    List<T> theList,
    int chunkSize
)
{
    List<List<T>> result = theList
        .Select((x, i) => new {
            data = x,
            indexgroup = i / chunkSize
        })
        .GroupBy(x => x.indexgroup, x => x.data)
        .Select(g => new List<T>(g))
        .ToList();

    return result;
}

Answer 3

What about this one?

var input = new List<string> { "a", "g", "e", "w", "p", "s", "q", "f", "x", "y", "i", "m", "c" };
var k = 3

var res = Enumerable.Range(0, (input.Count - 1) / k + 1)
                    .Select(i => input.GetRange(i * k, Math.Min(k, input.Count - i * k)))
                    .ToList();

As far as I know, GetRange() is linear in terms of number of items taken. So this should perform well.