Ruby: adding a new element to each array in an array, such that the new element is the downcased version of an existing element

Question

if

@users = User.all.group_by(&:iso).map{|k,v| [k, v.count]}

returns

 [["GB", 1], ["GI", 3], ["BD", 1]]

Why can't I do this

 @users = User.all.group_by(&:iso).map{|k,v| [k, v.count, k.downcase]}

to get

[["GB", 1, "gb"], ["GI", 3, "gi"], ["BD", 1, "bd"]]

I am getting the error

      undefined method `downcase' for nil:NilClass

How do I get this.

If I do

   @user_json = User.all.group_by(&:iso).map{|k,v| [k, v.count, k.inspect]}

I get

   [["GB", 1, "\"GB\""], ["GI", 3, "\"GI\""], ["BD", 1, "\"BD\""]

and then

  @user_json = User.all.group_by(&:iso).map{|k,v| [k, v.count, k.inspect.downcase]}

 [["GB", 1, "\"gb\""], ["GI", 3, "\"gi\""], ["BD", 1, "\"bd\""]

V. confused

FOR MORE DETAILS - THIS WORKS (but if it is wrong and can't explain why)

I am trying to build a JSON array with the structure:

   [{"code":"GB","value":1,"flag":"gb"},{"code":"GI","value":3,"flag":"gi"},{"code":"BD","value":1,"flag":"bd"}]

My controller code

     def global_chart
          @user_json = User.all.group_by(&:iso).map{|k,v| [k, v.count, k.to_s.downcase]}.map {|c, v | ["code" => c, "value" => v, "flag" => c.to_s.downcase]}.flatten.to_json
          render 'users/charts/global'
    end

This works ( the @user_json variable has the right structure) however I can't explain the behaviour above....

so one of your 'iso' is empty. try this User.all.group_by(&:iso).map{|k,v| [k, v.count, k.try(:downcase)]} — fl00r
– fl00r, Commented Aug 19, 2015 at 15:52
With your code I get: undefined local variable or method `downcase' for #<UsersController:0x007fdab38110b0> — GhostRider
– GhostRider, Commented Aug 19, 2015 at 15:52

fl00r · Accepted Answer · 2015-08-19 16:06:30Z

Your code

@users = User.all.group_by(&:iso).map{ |k,v| [k, v.count] }

is absolutely valid and its output shows us that you have got only three iso groups. Then

@users = User.all.group_by(&:iso).map{ |k,v| [k, v.count, k.downcase] }

is absolutely valid code as well. But you get an error undefined method 'downcase' for nil:NilClass which tells us that one of iso values is nil. Which is not true from your first example output.

After that, your third snippet

User.all.group_by(&:iso).map{ |k,v| [k, v.count, k.inspect.downcase] }

which is again correct, returns the same output as first one (I mean same sample of iso).

So somewhere in your code is bug. I believe it is close to provided piece of code. You could show whole controller's code to see maybe the problem is on the surface.

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