Count array keys possible?

rubyonrails-talk
#1

departures = [ 'AMS', 'BCN', 'BBK' ]
sums = {}
departures.each do |d|
  sums[d] ||= 0
  sums[d] = sums[d] + 1
end
puts( sums )

#2

Maurício Linhares wrote:

departures = [ 'AMS', 'BCN', 'BBK' ]
sums = {}
departures.each do |d|
  sums[d] ||= 0
  sums[d] = sums[d] + 1
end
puts( sums )

-
Maur�cio Linhares
http://alinhavado.wordpress.com/ (pt-br) | http://blog.codevader.com/
(en)

On Tue, Feb 24, 2009 at 2:57 PM, Remco Swoany

Hi Maurício,

Thanks for your reply.

I have more bookings from the same departures, like this:

departures = [ 'AMS', 'BCN', 'BKK', 'AMS', 'AMS', 'BKK']

Then i want to count the departures, like this based on the array above:

AMS => '3'
BCN => '1'
BKK => '2'

Is this possibly?

(the objective is to store the values in a graph for management-info)

Thanks in advance..

remco

#3

Why don't you do it at the database with an order by?

#4

Maurício Linhares wrote:

Why don't you do it at the database with an order by?

-
Maurício Linhares
http://alinhavado.wordpress.com/ (pt-br) | http://blog.codevader.com/
(en)

On Wed, Feb 25, 2009 at 1:04 PM, Remco Swoany

hmm...i don't now how to count the values through the order_by condition
(yep..i am newbie)

grtz..remco

#5

Ok, so this is the best time to start learning SQL, here's a good
start -> http://oreilly.com/catalog/9780596526849/

Here's how the query would look like:

SELECT departure, COUNT(*) AS departures_count FROM bookings GROUP BY departure

#6

Ok, so this is the best time to start learning SQL, here's a good
start -> http://oreilly.com/catalog/9780596526849/

Here's how the query would look like:

SELECT departure, COUNT(*) AS departures_count FROM bookings GROUP BY departure

-
Maurício Linhares
http://alinhavado.wordpress.com/ (pt-br) | http://blog.codevader.com/ (en)

You can do some of this with ActiveRecord, too. (Note this is my own little extension so don't go looking in ActiveRecord documentation for this particular module.)

module ActiveRecord
   module Groups
     def groups(*columns)
       return if columns.empty?
       options = columns.last.is_a?(Hash) ? columns.pop.dup : {}
       select = columns.join(',') + ',count(*) AS count_all'
       group = columns.join(',')
       columns = (columns + ['count_all']).map{|c|c.to_s}
       find(:all, :select => select, :conditions => options.delete(:conditions),
            :group => group).map {|rec| rec.attributes(:only => columns).values_at(*columns) }
     end
   end
end

require 'pp'

pp Booking.count # so the Booking model class will exist
class Booking
   extend ActiveRecord::Groups
end

cols = [ :departure ]
result = Booking.groups(*cols)

# which gives something like
#=> [ ["AMS", 3 ], ["BCN", 1], ["BKK", 2] ]

# or write that out to a CSV file
require 'fastercsv'
filename = 'counts.csv'
FasterCSV.open(filename, 'w') do |csv|
   csv << cols
   result.each {|r| csv << r }
end
puts "%5d rows in %s"%[result.size, filename]

Exercises for the reader (the OP, in particular):
* look at how the :select option can limit the attributes created in the model
* read how the :group option works on ActiveRecord::Base.find
* look at the #attributes method of a model and the Hash#values_at method

-Rob

Rob Biedenharn http://agileconsultingllc.com
Rob@AgileConsultingLLC.com