https://communities.sas.com/t5/SAS-Programming/changing-a-percentage-or-set-of-a-vars-observations/m-p/20177#M3121 What is the simplest way to change a percentage of a vars observations in a data set based on a condition on that single var? <BR /> <BR /> For example: I want to change 50% of the observations in a data set where var A = 1 to var A = 2? (50 current obs where A =1 are to be changed to 25 obs where A = 1 and 25 where A = 2.)<BR /> <BR /> Even the ability to change x-number of obs where var A = 1 to A = 2 would work. <BR /> <BR /> For example: 100 obs where A = 1; A is changed to 2 <BR /> <BR /> Normally I have the luxury of a second variable to condition against but in this case I don't have anything to use.<BR /> <BR /> Thanks. Wed, 12 May 2010 07:01:54 GMT veblen 2010-05-12T07:01:54Z https://communities.sas.com/t5/SAS-Programming/changing-a-percentage-or-set-of-a-vars-observations/m-p/20177#M3121 What is the simplest way to change a percentage of a vars observations in a data set based on a condition on that single var? <BR /> <BR /> For example: I want to change 50% of the observations in a data set where var A = 1 to var A = 2? (50 current obs where A =1 are to be changed to 25 obs where A = 1 and 25 where A = 2.)<BR /> <BR /> Even the ability to change x-number of obs where var A = 1 to A = 2 would work. <BR /> <BR /> For example: 100 obs where A = 1; A is changed to 2 <BR /> <BR /> Normally I have the luxury of a second variable to condition against but in this case I don't have anything to use.<BR /> <BR /> Thanks. Wed, 12 May 2010 07:01:54 GMT https://communities.sas.com/t5/SAS-Programming/changing-a-percentage-or-set-of-a-vars-observations/m-p/20177#M3121 veblen 2010-05-12T07:01:54Z https://communities.sas.com/t5/SAS-Programming/changing-a-percentage-or-set-of-a-vars-observations/m-p/20178#M3122 If it doesn't have to be exatly 50/50 then you could use ranuni() in the way:<BR /> <BR /> if a=1 then<BR /> do;<BR /> if ranuni()&gt;0.5 then a=2;<BR /> end;<BR /> <BR /> If it has to be exactly 50/50 but doesn't have to be random then you just could count the total number of obs where A=1 in a first pass through the data and then in a second pass set half of these obs where A=1 to A=2.<BR /> <BR /> If it has to be exactly 50/50 but random which record is set to A=2 then it's getting a bit harder. <BR /> You would still have to count the total number of obs where A=1 in a first pass through the data but then use a more sophisticated way for assigning 50% of obs where A=1 with A=2.<BR /> The approach I have in mind is mainly the same like picking a random sample (only that instead of writing the data to an sample data set you would assign the value 2 to A). This is the link to the code of how to pick the values together with some explanations: <A href="http://groups.google.com/group/comp.soft-sys.sas/browse_thread/thread/231bef19aaf0f2b1/fdabf8498967b267?lnk=gst&amp;q=patrick+random#fdabf8498967b267" target="_blank">http://groups.google.com/group/comp.soft-sys.sas/browse_thread/thread/231bef19aaf0f2b1/fdabf8498967b267?lnk=gst&amp;q=patrick+random#fdabf8498967b267</A><BR /> <BR /> HTH<BR /> Patrick Wed, 12 May 2010 13:36:07 GMT https://communities.sas.com/t5/SAS-Programming/changing-a-percentage-or-set-of-a-vars-observations/m-p/20178#M3122 Patrick 2010-05-12T13:36:07Z https://communities.sas.com/t5/SAS-Programming/changing-a-percentage-or-set-of-a-vars-observations/m-p/20179#M3123 THANK YOU Patrick!<BR /> <BR /> It worked like a charm. Thu, 13 May 2010 16:06:35 GMT https://communities.sas.com/t5/SAS-Programming/changing-a-percentage-or-set-of-a-vars-observations/m-p/20179#M3123 veblen 2010-05-13T16:06:35Z