why does this enumerable list split up?

Question

I try to take 3 rows at a time from a List of string but its not working as expected. Consider this code...

var listOfStrings = new List<string>
{
    "String 1",
    "String 2",
    "String 3",
    "String 4",
    "String 5",
    "String 6"
};

foreach (var x in listOfStrings.Take(3).ToList())
{
    var currRows = x.ToList();

    // currRows should have 3 items
    foreach (var itm in currRows)
    {

    }
}

The first run I expect currRows to have 3 items (String 1, 2 and 3), the second time I expect to have these 3 items (String 4, 5 and 6). But when I run this currRows only contains for example "String 1" and this is split up character by character?!

What am I missing here?

Answer 1

But when I run this currRows only contains for example "String 1" and this is split up character by character?!

That's because Enumerable.Take will take the requested amount of items from the IEnumerable<T>. This makes your x variable be of type string, which you later call ToList() on, effectively creating a List<char>, which isn't what you want.

You can use MoreLINQ which has a Batch extension method which does exactly what you want. It returns an IEnumerable<IEnumerable<T>>:

foreach (var batch in listOfStrings.Batch(3))
{
    // batch is an IEnumerable<T>, and will have 3 items.
    foreach (var item in batch)
    {

    }
}

Another possibility is to create that extension method yourself. This is taken from this answer:

public static class EnumerableExtensions
{
    public static IEnumerable<IEnumerable<T>> Batch<T>(this IEnumerable<T> items,
                                                       int maxItems)
    {
        return items.Select((item, inx) => new { item, inx })
                    .GroupBy(x => x.inx / maxItems)
                    .Select(g => g.Select(x => x.item));
    }
}