This class provides a simple way to apply transformations and filters that get run while you are aggregating data. This is used primarily to build constrained wrappers to Ruport::Data::Table, but can be used with abstract data structures as well.
Table Example:
t = Table(%w[a b c]) do |feeder| feeder.filter { |r| r.a < 5 } feeder.transform { |r| r.b = "B: #{r.b}"} feeder << [1,2,3] feeder << [7,1,2] feeder << { "a" => 3, "b" => 6, "c" => 7 } end t.length #=> 2 t.column("b") #=> ["B: 2","B: 6"]
Filters and transforms are added in a sequential order to a single list of constraints. You could add some constraints and then append some data, then add additional constraints, or even build up dynamic constraints if you'd like.
Wrapping an arbitrary data object:
In order to make Data::Feeder work with an object other than Data::Table, it must implement two things:
* A method called feed_element that accepts a single argument. When Feeder#<< is called, the object to be appended is converted by this method, and then yielded to the filters / transforms. * A meaningful #<< method. Feeder#<< simply delegates this to the wrapped object once the filters and transforms have been applied, so be sure that the object returned by feed_element is one that can be used by your #<< method.
Here is a sample implementation of wrapping a feeder around an Array.
class Array def feed_element(element) element end end int_array = [] feeder = Ruport::Data::Feeder.new(int_array) feeder.filter { |r| r.kind_of?(Integer) } feeder << 1 << "5" << 4.7 << "kitten" << 4 int_array #=> [1, 4]
Creates a new Data::Feeder, wrapping the data object provided.
# File lib/ruport/data/feeder.rb, line 64 def initialize(data) @data = data @constraints = [] end
Constrained append operation.
Before filters and transforms are run, the element to be appended is first converted by data.feed_element(some_element)
Filters and transforms are then run sequentially, and if the constraints are met, it is appended using data << some_element.
# File lib/ruport/data/feeder.rb, line 80 def <<(element) feed_element = data.feed_element(element) @constraints.each do |type,block| if type == :filter return self unless block[feed_element] else block[feed_element] end end data << feed_element return self end
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