Multiple Series Line Chart Using Chartkick and Rails

I'm trying to setup a multiple series line chart that shows monthly total exams by modality.

Something similar to this chart:

I want the modalities to be colored: (CT, MR, US, XR, MG, BD, NM)

The monthly date (to_date) will be the X-Axis data label.

Exams model:

has_many :modalities

Modality model:

belongs_to :exam

I have a monthly_modalities action on my Charts controller:

  def monthly_modalities
    chart_data = Modality.joins(:exam).map {|m|
      {name: m.name, data: m.exam.to_date}
    }
    render json: chart_data.each do |e|
      {name: :name, data: e.group_by_month(:to_date, format: '%b', range: 1.year).sum(:total).chart_json}
    end
  end

Here's the chart that is created:

The problem is that repeating modalities aren't grouping together and the monthly date (to_date) isn't showing on the X-Axis data label.

I ended up asking another question regarding this issue but even more specific about how I was looping through and outputting the data.

Here's the way I solved this:

now = Time.now

chart_data = Modality.joins(:exam)
                     .where(exams: {from_date: (now - 1.year)..now}).map {|m|
  {name: m.name, data: {m.exam.from_date => m.total}}}

@exams = chart_data.group_by {|h| h[:name]}
             .map {|k, v| {name: k, data: v.map {|h| h[:data]}.reduce(&:merge)}}

Here's the hash needed for displaying the chart:

[
  {:name=>"MR", :data=>{Wed, 01 Feb 2017=>41, Wed, 01 Mar 2017=>66, Sat, 01 Apr 2017=>73, Sun, 01 Jan 2017=>44}}, 
  {:name=>"CT", :data=>{Wed, 01 Feb 2017=>4, Wed, 01 Mar 2017=>6, Sat, 01 Apr 2017=>8, Sun, 01 Jan 2017=>52}}, 
  {:name=>"XR", :data=>{Wed, 01 Mar 2017=>1}}, 
  {:name=>"US", :data=>{Sat, 01 Apr 2017=>1, Sun, 01 Jan 2017=>1}}
]

In my view, I rendered the chart like so:

<%= line_chart @exams %>

And the correct chart: