Question

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Rails ActiveRecord group_by & sum db results for use with Lazy HighCharts

I am completely new to RoR/Ruby and i am using Lazy High Charts gem to generate some purdy charts based on some database information.

I have tried the answers that were provided but i am still a bit confused as to how to do this..

I need to sum amount_used, and billed_amount and group by month/year (e.g; Aug/2012)

The end result will be something similar to a dual axis chart with two series "Amount Used", and "Cost".. This information is specific to a certain account_id.

Invoices table

+---------------+--------------+------+-----+---------+----------------+
| Field         | Type         | Null | Key | Default | Extra          |
+---------------+--------------+------+-----+---------+----------------+
| id            | int(11)      | NO   | PRI | NULL    | auto_increment |
| account_id    | int(11)      | YES  |     | NULL    |                |
| invoice_date  | varchar(255) | YES  |     | NULL    |                |
| amount_used   | float        | YES  |     | NULL    |                |
| billed_amount | float        | YES  |     | NULL    |                |
| comments      | text         | YES  |     | NULL    |                |
| created_at    | datetime     | NO   |     | NULL    |                |
| updated_at    | datetime     | NO   |     | NULL    |                |
+---------------+--------------+------+-----+---------+----------------+

Controller Chart Code

@account = Account.find(params[:id])
@invoices = Invoice.where("account_id = #{@account.id}").order("invoice_date DESC")

@h = LazyHighCharts::HighChart.new('area') do |f|
  f.options[:chart][:defaultSeriesType] = "area"
  #Sample dates right now, should be the grouped_by :invoice_date
  f.xAxis( :categories => ['May', 'Jun', 'Jul'] )
  f.yAxis([
    {
      :title => { :text => "Amount Used" }
    },
    {
      :title => { :text => "Cost" },
      :opposite => true
    }
  ])
  #Sample data right now, should be the summed amounts of the :amount_used correpsonding for each above grouped invoice_date
  f.series(:name => "Amount Used", :data => [100,300,500] )
  #Sample data right now, should be the summed amounts of the :billed_amount correpsonding for each above grouped invoice date
  f.series(:name => "Cost", :yAxis => 1, :data => [200,400,600] )
end 

Answer 1

The key is to use Enumerable#group_by to find all the rows with the same month and then add them together:

require 'date'

# Simulate rows from your DB
Row = Struct.new(:date,:amount)
rows = DATA.read.scan(/(\S+) - (\d+)/).map do |date,amount|
    Row.new( Date.strptime(date,'%m/%d/%y'), amount.to_i )
end

sum_by_month = rows.sort_by(&:date).group_by do |row|
    row.date.strftime('%b/%Y')
end.map do |year_and_month,sub_rows|
    [ year_and_month, sub_rows.map(&:amount).inject(:+) ]
end

p sum_by_month
#=> [
#=>   ["Aug/2012", 22000],
#=>   ["Sep/2012", 5000],
#=>   ["Oct/2012", 76000]
#=> ]

__END__
08/01/12 - 10000
08/16/12 - 12000
09/13/12 - 5000
10/12/12 - 76000

For your specific use case, you could use this like:

<table><thead><tr><td></td>
  <%sum_by_month.each do |month,total|%>
    <th scope="col"><%=month%></th>
  <%end%>
</thead><tbody>
  <tr><th>Usage:</th>
  <%sum_by_month.each do |month,total|%>
    <td><%=total%></td>
  <%end%></tr>
</tbody></table>

---

Alternatively, here’s a more direct approach (that I do not recommend):

sum_by_month = {}
last_month = nil
total      = nil
@invoices.each do |inv|
  month = inv.date.strftime('%b/%Y')
  unless last_month==month
    sum_by_month[month] = total if last_month
    last_month = month
    total      = 0
  end
  total += inv.amount
end

# Make sure to add in the very last month
sum_by_month[month] = total if last_month