Question

Assume I have an enumerable object enum and now I want to get the third item.

I know one of a general approach is convert into an array and then access with index like:

enum.to_a[2]

But this way will create a temporary array and it might be inefficient.

Now I use:

enum.each_with_index {|v, i| break v if i == 2}

But this is quite ugly and redundant.

What’s the most efficient way to do this?

Answer 1

You could use take to peel off the first three elements and then last to grab the third element from the array that take gives you:

third = enum.take(3).last

If you don’t want to generate any arrays at all then perhaps:

# If enum isn't an Enumerator then 'enum = enum.to_enum' or 'enum = enum.each'
# to make it one.
(3 - 1).times { enum.next }
third = enum.next