Question

Ruby noob here!

I have an array of structs that look like this

Token = Struct.new(:token, :ordinal)

So an array of these would look like this, in tabular form:

 Token | Ordinal
 ---------------
    C  | 2
    CC | 3
    C  | 5

And I want to group by the “token” (i.e. the left hand column) of the struct and get a count, but also preserve the “ordinal” element. So the above would look like this

 Token | Merged Ordinal | Count
 ------------------------------
    C  | 2, 5           | 2
    CC | 3              | 1

Notice that the last column is a count of the grouped tokens and the middle column merges the “ordinal”. The first column (“Token”) can contain a variable number of characters, and I want to group on these.

I have tried various methods, using group_by (I can get the count, but not the middle column), inject, iterating (does not seem very functional) but I just can’t get it right, partly because I don’t have a good grasp of Ruby and the available operations / functions.

I have also had a good look around SO, but I am not getting very far.

Any help, pointers would be much appreciated!

Answer 1

Use Enumerable#group_by to do the grouping for you and use the resulting hash to get what you want with map or similar.

structs.group_by(&:token).map do |token, with_same_token|
  [token, with_same_token.map(&:ordinal), with_same_token.size]
end