Drop the last item with LINQ

Question

Seems like a trivial task with LINQ (and probably it is), but I cannot figure out how to drop the last item of squence with LINQ. Using Take and passing the length of the sequence - 1 works fine of course. However, that approach seems quite inconvienient when chaining up multiple LINQ in a single line of code.

IEnumerable<T> someList ....

// this works fine
var result = someList.Take(someList.Count() - 1);


// but what if I'm chaining LINQ ?
var result = someList.Where(...).DropLast().Select(...)......;

// Will I have to break this up?
var temp = someList.Where(...);
var result = temp.Take(temp.Count() - 1).Select(...)........;

In Python, I could just do seq[0:-1]. I tried passing -1 to Take method, but it does not seem to do what I need.

Answer 1

For .NET Core 2+ and .NET Standard 2.1 (planned), you can use .SkipLast(1).

For other platforms, you could write your own LINQ query operator (that is, an extension method on IEnumerable<T>), for example:

static IEnumerable<T> SkipLast<T>(this IEnumerable<T> source)
{
    using (var e = source.GetEnumerator())
    {
        if (e.MoveNext())
        {
            for (var value = e.Current; e.MoveNext(); value = e.Current)
            {
                yield return value;
            }
        }
    }
}

Unlike other approaches such as xs.Take(xs.Count() - 1), the above will process a sequence only once.

Answer 2

someList.Reverse().Skip(1).Reverse()

Answer 3

You can quite easily do this with an extension method, either using the form you've already found, or perhaps a combination of Take and Count

public static IEnumerable<T> DropLast<T>(this IEnumerable<T> enumerable)
{
  return enumerable.Take(enumerable.Count()-1);
}