justaddwater.dk

In a Ruby on Rails app, I wanted a list to be at least of two items. This could be done in several ways.

Here is a first naïve impementation:

# Naïve implementation, just return whatever number I need
def sum_up_a(existing)
  return 2 if existing == 0
  return 1 if existing == 1
  return 0
end

sum_up_a(0)   # => 2
sum_up_a(1)   # => 1
sum_up_a(2)   # => 0
sum_up_a(3)   # => 0
sum_up_a(10)  # => 0

A slightly improved version could investigate number of existing, and return the diff only if needed:

MIN_COUNT = 2
# slightly improved with less conditionals
def sum_up_b(existing)
  return 0 if existing >= MIN_COUNT
  MIN_COUNT - existing
end

sum_up_b(0)   # => 2
sum_up_b(1)   # => 1
sum_up_b(2)   # => 0
sum_up_b(3)   # => 0
sum_up_b(10)  # => 0

Now, my favourite. If you look at the result of “MIN_COUNT – existing”. This number is negative or zero if we dont want extra rows. This means that we can rewrite the algorithm without any conditional logic like this:

# my favorite: return the biggest number either 0 or the difference
# Works well because difference is only positive for numbers where I 
# need some extra rows
def sum_up_c(existing)
  [MIN_COUNT - existing, 0].max 
end

sum_up_c(0)   # => 2
sum_up_c(1)   # => 1
sum_up_c(2)   # => 0
sum_up_c(3)   # => 0
sum_up_c(10)  # => 0

I like the latter, since too many conditional statements tend to clutter the logic. Just a short tip and a reminder for myself next time I run into this kind of problem.

Complete example gist avalilable on Github:

This entry was posted by Jesper Rønn-Jensen on Sunday, December 13th, 2015 at 21:20 (GMT-1) and is filed under Code, Ruby on Rails. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.