topic Re: subsetting random observations in SAS Programming

subsetting random observations

deleted_user — Tue, 12 Aug 2008 06:41:20 GMT

Hi,

I have a data set in which i want to subset a sample with a condition. In the subset I want to pull out 1.5 % of random observations of a variable and take the average of it.

I could do the first part of this task to pull the subset with a condition (using WHERE clause).

I'm trying to figure out how I can pull 1.5 % of random observations of the variable.

After that, I think I can use Avg function to get a mean of it.

Appreciate you help!

Re: subsetting random observations

Olivier — Tue, 12 Aug 2008 06:55:49 GMT

Hi.
Check out the Surveyselect procedure if you have licence for SAS/STAT.
If not, one usual way is to code :
1) a data step that creates a random variable (using the RANUNI or RAND functions)
2) sort the new dataset by this random variable
3) keep only the x first observations of the sorted dataset.
This last way of doing is just like shuffling cards.

Olivier

Re: subsetting random observations

LinusH — Tue, 12 Aug 2008 07:28:12 GMT

You can also do a subsetting if in the first datastep (on the new "ranuni"-variable). Then there is no need to sort and read the data a third time.

Regards,
Linus

Re: subsetting random observations

Patrick — Tue, 12 Aug 2008 10:39:08 GMT

The code below (second data step) is almost what SAS provides in the training for the SAS certification.
HTH
Patrick

data work.rsubset;
set (where=( run;

data work.rsubset(drop=obsleft sampsize);
/* sampsize=10; */
sampsize=ceil(totobs*0.015);
obsleft=totobs;
do while(sampsize>0);
pickit+1;
if ranuni(0) set sasuser.revenue point=pickit
nobs=totobs;
output;
sampsize=sampsize-1;
end;
obsleft=obsleft-1;
end;
stop;
run;

Message was edited by: Patrick Message was edited by: Patrick

Re: subsetting random observations

mkeintz — Tue, 14 Aug 2012 12:47:50 GMT

San:

Are you asking for 1.5% randomly selected from the entire data set? Or do you want 1.5% of the subset that meets a given condition (you said "subset a random sample with a condition"). If it's the latter, then your question hasn't been answered yet.

Re: subsetting random observations

ArtC — Tue, 14 Aug 2012 18:41:35 GMT

We should also ask whether the subset is selected with or without replacement. For small subsets of a large data set it probably does not matter a lot, but....