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Scalding

Scalding is a Scala library that makes it easy to specify Hadoop MapReduce jobs. Scalding is built on top of Cascading, a Java library that abstracts away low-level Hadoop details. Scalding is comparable to Pig, but offers tight integration with Scala, bringing advantages of Scala to your MapReduce jobs.

Scalding Logo

Current version: 0.12.0rc4

Word Count

Hadoop is a distributed system for counting words. Here is how it's done in Scalding.

package com.twitter.scalding.examples

import com.twitter.scalding._

class WordCountJob(args : Args) extends Job(args) {
  TextLine( args("input") )
    .flatMap('line -> 'word) { line : String => tokenize(line) }
    .groupBy('word) { _.size }
    .write( Tsv( args("output") ) )

  // Split a piece of text into individual words.
  def tokenize(text : String) : Array[String] = {
    // Lowercase each word and remove punctuation.
    text.toLowerCase.replaceAll("[^a-zA-Z0-9\\s]", "").split("\\s+")
  }
}

Notice that the tokenize function, which is standard Scala, integrates naturally with the rest of the MapReduce job. This is a very powerful feature of Scalding. (Compare it to the use of UDFs in Pig.)

You can find more example code under examples/. If you're interested in comparing Scalding to other languages, see our Rosetta Code page, which has several MapReduce tasks in Scalding and other frameworks (e.g., Pig and Hadoop Streaming).

Documentation and Getting Started

Please feel free to use the beautiful Scalding logo artwork anywhere.

Building

There is a script (called sbt) in the root that loads the correct sbt version to build:

  1. ./sbt update (takes 2 minutes or more)
  2. ./sbt test
  3. ./sbt assembly (needed to make the jar used by the scald.rb script)

The test suite takes a while to run. When you're in sbt, here's a shortcut to run just one test:

> test-only com.twitter.scalding.FileSourceTest

Please refer to FAQ page if you encounter problems when using sbt.

We use Travis CI to verify the build: Build Status

Scalding modules are available from maven central.

The current groupid and version for all modules is, respectively, "com.twitter" and 0.11.0.

Current published artifacts are

  • scalding-core_2.9.3
  • scalding-core_2.10
  • scalding-args_2.9.3
  • scalding-args_2.10
  • scalding-date_2.9.3
  • scalding-date_2.10
  • scalding-commons_2.9.3
  • scalding-commons_2.10
  • scalding-avro_2.9.3
  • scalding-avro_2.10
  • scalding-parquet_2.9.3
  • scalding-parquet_2.10
  • scalding-repl_2.9.3
  • scalding-repl_2.10

The suffix denotes the scala version.

Adopters

  • Ebay
  • Etsy
  • Sharethrough
  • Snowplow Analytics
  • Soundcloud
  • Twitter

To see a full list of users or to add yourself, see the wiki

Contact

For user questions, we are using the cascading-user mailing list for discussions: http://groups.google.com/group/cascading-user

For scalding development (internals, extending, release planning): https://groups.google.com/forum/#!forum/scalding-dev

In the remote possibility that there exist bugs in this code, please report them to: https://github.com/twitter/scalding/issues

Follow @Scalding on Twitter for updates.

Chat (IRC): freenode channel: #scalding

Authors:

Thanks for assistance and contributions:

A full list of contributors can be found on GitHub.

License

Copyright 2013 Twitter, Inc.

Licensed under the Apache License, Version 2.0: http://www.apache.org/licenses/LICENSE-2.0