CHIA-MING LIN thinks this is interesting: (v) => (v, 1) From 4. Working with Key/Value Pairs from Learning Spark by Matei Zaharia, Patrick Wendell, Andy Konwinski, Holden Karau Publisher: O'Reilly Media, Inc. Released: February 2015 Note createCombiner: the return of this creator determines the type of accumulator. Share this highlight http://learning.oreilly.com/a/learning-spark/1246665/ Twitter Facebook Google Plus Email Get Instant Access Now Start a Free Trial Have an account? Sign in.