tip_returning_group_by_index_by.rb

def get_vehicle_report(vehicle_id)
  vehicle = Vehicle.find(vehicle_id)
  returning Report.new(vehicle_id, vehicle.year, vehicle.description) do |report|
    if report.something.nil?
      owner = vehicle.owner
      # ...
    end
  end
end



## group_by
#  - Partition a collection based on the value returned by a block
>> (1..20).group_by {|n| n%3}
#   => {0=>[3,6,9,12,15,18],
#       1=>[1,4,7,10,13,16,19],
#       2=>[2,5,8,11,14,17,20]}

## index_by
#  - Convert a collection into a hash where keys are values returned by a block
>> (1..5).index_by {|n| n*10}
#   => {50=>5, 40=>4, 30=>3, 20=>2, 10=>1}

## sum
#  - Sum the values returned by the block
>> [1,3,5,7,9].sum
#   => 25
>> [1,3,5,7,9].sum {|n| n*n}
#   => 165
>> Orders.find(:all).sum {|o| o.total}
#   => 12345.67



## in_groups_of
#  - Partitions an array into chunks of N elements
>> %w{ a b c d e f g h i j }.in_groups_of(3)
#   => [["a", "b", "c"],
#       ["d", "e", "f"],
#       ["g", "h", "i"],
#       ["j", nil, nil]]

## to_sentence
#  - Like #join on steroids (sometimes useful for listing tags)
>> names = %w{ Ryan Paul Heath }
>> names.to_sentence
#   => "Ryan, Paul, and Heath"
>> names.to_sentence(:connector => "and also")
#   => "Ryan, Paul, and also Heath"