[ https://issues.apache.org/jira/browse/HIVE-3455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13454465#comment-13454465 ]
Maxim Bolotin commented on HIVE-3455: ------------------------------------- the test, the correct answer is 1. hive> select * from max_corr ; OK 1 2 2 4 3 6 Time taken: 2.304 seconds hive> select corr(a,b) from max_corr ; Total MapReduce jobs = 1 Launching Job 1 out of 1 Number of reduce tasks determined at compile time: 1 In order to change the average load for a reducer (in bytes): set hive.exec.reducers.bytes.per.reducer=<number> In order to limit the maximum number of reducers: set hive.exec.reducers.max=<number> In order to set a constant number of reducers: set mapred.reduce.tasks=<number> Starting Job = job_201207232322_2781, Tracking URL = http://*****/jobdetails.jsp?jobid=job_201207232322_2781 Kill Command = /usr/lib/hadoop/bin/hadoop job -Dmapred.job.tracker=hdfs://***** -kill job_201207232322_2781 2012-09-12 10:04:17,663 Stage-1 map = 0%, reduce = 0% 2012-09-12 10:04:20,681 Stage-1 map = 100%, reduce = 0% 2012-09-12 10:04:27,720 Stage-1 map = 100%, reduce = 33% 2012-09-12 10:04:28,728 Stage-1 map = 100%, reduce = 100% Ended Job = job_201207232322_2781 OK 0.27586206896551724 Time taken: 15.088 seconds hive> > ANSI CORR(X,Y) is incorrect > --------------------------- > > Key: HIVE-3455 > URL: https://issues.apache.org/jira/browse/HIVE-3455 > Project: Hive > Issue Type: Bug > Components: UDF > Affects Versions: 0.7.1, 0.8.0, 0.9.0 > Reporter: Maxim Bolotin > > A simple test with 2 collinear vectors returns a wrong result. > The problem is the merge of variances, file: > http://svn.apache.org/viewvc/hive/trunk/ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFCorrelation.java?revision=1157222&view=markup > lines: > 347: myagg.xvar += xvarB + (xavgA-xavgB) * (xavgA-xavgB) * myagg.count; > 348: myagg.yvar += yvarB + (yavgA-yavgB) * (yavgA-yavgB) * myagg.count; > the correct merge should be like this: > 347: myagg.xvar += xvarB+(xavgA - xavgB)*(xavgA-xavgB)/myagg.count*nA*nB; > 348: myagg.yvar += yvarB+(yavgA - yavgB)*(yavgA-yavgB)/myagg.count*nA*nB; -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira