Remove adjacent identical elements in a Ruby Array?

Question

Ruby 1.8.6

I have an array containing numerical values. I want to reduce it such that sequences of the same value are reduced to a single instance of that value.

Answer 1

I can think only of this

a.each_with_index{|item,i| a[i] = nil if a[i] == a[i+1] }.compact

but it is more or less the same.