Remove temp with functional

gistfile1.rb

###
### First approach
###

[class_months(es, class_name)].flat_map { |range| [range.count.to_f, month_range(range.first, upto_date).count] }
                              .reduce(:/) * 100

###
### Second Approach
###

# define operator `?` as `memoize function`

?class_months(es, class_name).count.to_f / month_range(?class_months(es, class_name).first, upto_date).count * 100.0