Question

I’m new to ruby, and I’ve been googling for hours, but I can’t figure this one out. It looks like it should be really easy so I’m getting pretty frustrated.

I’m working in ruby and need to compare 2 arrays of symbols for a true or false return.

array1 = [:a, :c]
array2 = [:a, :b, :c]

The comparison I need to do, is to see if array2 includes all the elements of array1.
In this case array2 includes array1, but array1 does not include array2.

I tried:

array2.to_s.include?(array1.to_s) 

Which only returns true if they are in the same order because it needs to convert to a string for comparison. So as is it returns false (not what I’m looking for), but if array2 = [:a, :c, :b] it would be true. Is there a more appropriate way of making this comparison?

Answer 1

venj’s answer is fine for small arrays but might not perform well (this is debatable) for large arrays. Since you’re basically doing a set operation (“is Set(array1) a subset of Set(array2)?”), it makes sense to see how Ruby’s own Set library does this. Set has a subset? method, and taking a peek at its source we see that it’s short and sweet:

def subset?(set)
  set.is_a?(Set) or raise ArgumentError, "value must be a set"
  return false if set.size < size
  all? { |o| set.include?(o) }
end

We could just instantiate two Set objects from the arrays and call it a day, but it’s just as easy to distill it into a oneliner that operates directly on them:

array1 = [:a, :c]
array2 = [:a, :b, :c]

array1.length < array2.length && array1.all? {|el| array2.include? el }
# => true

array1 << :z
array1.length < array2.length && array1.all? {|el| array2.include? el }
# => false