From: Brian Candler <b.candler@...>
Date: 2009-02-26T00:46:57+09:00
Subject: Re: Newbie question > count array key?

Remco Swoany wrote:
> newbie question(i guess)
> 
> a = Bookings.find(:all, :conditions => [3.days.ago])
> a = [id : 1, departure : 'AMS', arrival => 'NY'],[id : 2, departure :
> 'AMS', arrival => 'BCN'],[id : 3, departure : 'AMS', arrival =>
> 'BKK'],[id : 4, departure : 'AMS', arrival => 'BKK'] ect.
> 
> The value of the key departure and arrival is dynamic based on
> table(3000 combinations) and the bookings
> 
> 
> I want to find the bookings and count the arrival and departure(s). I
> the case of the code above, i want the following output.
> 
> departure = AMS > total = 5
> arrival = BCN > total = 1
> arrival = NY > total = 1
> arrival = BKK > total = 2
> 
> How can i do this

You iterate through the rows, counting the values of interest.

Constructs you may find useful are:

(1) the 'each' method of the Array class (to iterate through your array)

  a.each do |booking|
    p booking
    # or do something else with it
  end

(2) Hashes, especially ones which have a default value of zero

  count = Hash.new(0)

  count["foo"] += 1
  count["bar"] += 1
  count["foo"] += 1

  # after this, count = {"foo"=>2, "bar"=>1}

(3) the 'each' method of the Hash class

  count.each do |key,value|
    puts "#{key}: #{value}"
  end

(4) The 'irb' shell, for trying these things out, or script/console if 
you are using Rails (the latter will also give you full access to your 
model classes)

$ irb
irb(main):001:0> count = Hash.new(0)
=> {}
irb(main):002:0> count["foo"] += 1
=> 1
irb(main):003:0> count["bar"] += 1
=> 1
irb(main):004:0> count["foo"] += 1
=> 2
irb(main):005:0> count
=> {"foo"=>2, "bar"=>1}

See your favourite Ruby documentation for more details on these topics. 
If you don't have any, then an old version of the Pickaxe book is 
browsable online for free here:
http://www.ruby-doc.org/docs/ProgrammingRuby/
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