Class: PiecePipe::MapStep

Inherits:
Step
  • Object
show all
Defined in:
lib/piece_pipe/map_step.rb

Overview

This type of Step is designed to produce key-value pairs in anticipation of a following aggregation step (see HashedAggregator).

Subclasses implement #map and can produce output via #emit(key, value). Zero-or-more pairs may be generted per #map invocation.

The output structure is in fact a Hash with two keys: :key and :value, eg

class CalorieCounter < PiecePipe::MapStep
  # Expects inputs to be a Hash with :person, :date and :calories.
  # Output will look like: { :key => ["Dave","2012-05-10"], :value => 6000 }
  def map(inputs)
    key = [inputs[:person], inputs[:date]]
    val = inputs[:calories]
    emit key, val
  end
end

Instance Attribute Summary

Attributes inherited from Step

#source

Instance Method Summary collapse

Methods inherited from Step

#to_enum

Instance Method Details

#emit(key, value) ⇒ Object 



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# File 'lib/piece_pipe/map_step.rb', line 30

def emit(key, value)
  produce key: key, value: value
end

#map(item) ⇒ Object 



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# File 'lib/piece_pipe/map_step.rb', line 26

def map(item)
  emit item, item
end

#process(item) ⇒ Object 



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# File 'lib/piece_pipe/map_step.rb', line 22

def process(item)
  map item
end