Kernel#itself method simply yields the object that it was called on:

1.itself
=> 1

You can group an array by an amount of occurrences like this:

[1, 2, 2, 3, 4, 5, 6].group_by { |item| item }

Or like this, using Kernel#itself:

[1, 2, 2, 3, 4, 5, 6].group_by(&:itself)