56 proc rank data=match2 out=match3 groups=10;
57 by year1;
58 var msmvttl;
59 ranks yeargroup;
60 run;
ERROR: Data set WORK.MATCH2 is not sorted in ascending sequence. The current by-group has year1 =
2009 and the next by-group has year1 = 1997.
NOTE: The SAS System stopped processing this step because of errors.
NOTE: There were 146 observations read from the data set WORK.MATCH2.
谁能告诉我这种错误是什么意思啊?多谢