Question

I am trying to run the following code:

dupe_groups = Activity.all.group_by { |e| e.non_id_attributes }.select{ |gr| gr.last.size > 1 }
      redundant_elements = dupe_groups.map { |group| group.last - [group.last.first] }.flatten
      redundant_elements.each(&:destroy)

However, I get the following error:

Activity.find(:all).group_by { |e| e.non_id_attributes }.select{ |gr| gr.last.size > 1 }
NoMethodError: undefined method `last' for #<Hash:0x00000107e505e8>
    from (irb):10:in `block in irb_binding'
    from (irb):10:in `select'
    from (irb):10
    from /usr/local/bin/irb:12:in `<main>'

How can I get this fella to work?

Answer 1

When you do a group_by you get a hash, the thing you group by is represented as the keys in the hash so when you select over it you should be doing .select{|key, values| …} and you can then values.size > 1

Although, when I look at this code, it has a smell to me. What are you actually trying to do?