Question

I am new to Ruby and I am trying to write a method that groups an array of words into anagram groups. Here is the code:

def combine_anagrams(words)
  dict = words.inject(Hash.new(0)) do |list,ws|
    key = sort_word(ws)
    if !list.has_key?(key)
      list[key] = []
    end
    list[key].push(ws)
    list             #What is this
  end
  return dict.values
end   

My question is what the statement list is for. If I take it out list becomes an array instead of hash.

Answer 1

Every method/block/etc. in Ruby returns something, and unless there is an early return statement, whatever the last statement in the method/block/etc. is, is what is returned.

In your case, having list be the last line in the block passed to inject ensures that list is returned by the block. When you remove it, the return value of list[key].push(ws) is returned, which obviously isn’t what you want.

Note that this behavior also makes using the return keyword when it is the last statement that would be executed otherwise is unnecessary (this includes the return you have at the end of your method). Though some prefer to be explicit that they intend to return something and use them even when not needed.

On an unrelated note: your if !list.has_key?(key) can be rewritten unless list.has_key?(key).