Differences
This shows you the differences between two versions of the page.
Both sides previous revision Previous revision | Next revision Both sides next revision | ||
courses:mapreduce-tutorial:step-29 [2012/01/31 14:41] straka |
courses:mapreduce-tutorial:step-29 [2012/02/05 18:23] straka |
||
---|---|---|---|
Line 1: | Line 1: | ||
====== MapReduce Tutorial : Custom sorting and grouping comparators. ====== | ====== MapReduce Tutorial : Custom sorting and grouping comparators. ====== | ||
+ | ====== Sorting comparator ====== | ||
+ | |||
+ | The keys are sorted before processed by a reducer, using a | ||
+ | [[http:// | ||
+ | |||
+ | ====== Grouping comparator ====== | ||
+ | |||
+ | In a reduce, it is guaranteed that keys are processed in ascending order. Sometimes it would be useful if the //values associated with one key// could also be processed in ascending order. | ||
---- | ---- | ||
Line 13: | Line 21: | ||
</ | </ | ||
</ | </ | ||
+ |