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README.md

lambda_map_reduce gem

A MapReduce implementation for use with lambdas.

Installation

Run gem install lambda_map_reduce on the command line or add gem 'lambda_map_reduce' to your project's Gemfile.

Usage

LambdaMapReduce.map_reduce takes an Enumerable, a mapper lambda, and a reducer lambda.

The mapper lambda is called once for every item in the Enumerable. It should take a single item and return an Array of [key, value] pairs.

The algorithm will shuffle all value items with the same key together, and pass the resulting [key, Array of values] Arrays to the reducer, which should return a single item.

The mapper and reducer may return nil. The result of the algorithm is the Array of items produced from each reducer call.

An example from the team_api gem's CrossReferencer class:

require 'lambda_map_reduce'

module TeamApi
  class CrossReferencer
    def self.create_tag_xrefs(site, items, category, xref_data)
      items_to_tags = lambda do |item|
        item_xref = xref_data.item_to_xref item
        item[category].map { |tag| [tag, item_xref] } unless item[category].nil?
      end
      create_tag_xrefs = lambda do |tag, item_xrefs|
        [tag, tag_xref(site, category, tag, item_xrefs)]
      end
      LambdaMapReduce.map_reduce(items, items_to_tags, create_tag_xrefs).to_h
    end
  end
end

Public domain

This project is in the worldwide public domain. As stated in CONTRIBUTING:

This project is in the public domain within the United States, and copyright and related rights in the work worldwide are waived through the CC0 1.0 Universal public domain dedication.

All contributions to this project will be released under the CC0 dedication. By submitting a pull request, you are agreeing to comply with this waiver of copyright interest.

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