topic Re: selecting IDs randomly from a dataset in SAS Programming

selecting IDs randomly from a dataset

Anita_n — Fri, 30 Jul 2021 15:05:55 GMT

Dear all,

I have this sample dataset :

data test;
input pat_id 2. sex $2. age 3. var1 $2. var2 $2. var3 $2. var4 $2. year 5.;
datalines;
1  F 25 A B C D 2001
1  F 25 E F G D 2002
2  F 35 C M N D 2010
2  F 35 E F V W 2020
15 M 55 A B C D 2011
15 M 55 E F G D 2010
15 M 55 U B C D 2011
15 M 55 j F K D 2010
15 M 55 X B C D 2009
15 M 55 E Y G D 2008
15 M 55 F Y T D 2008
11 F 60 A B C D 2001
11 F 60 E F G D 2002
11 F 60 U B C D 2015
11 F 60 j F K D 2004
11 F 60 X B C D 2010
11 F 60 E Y G D 2014
11 F 60 F Y T D 2008
11 F 60 S F G D 2003
11 F 60 V B G D 2012
11 F 60 K F K Q 2000
11 F 60 Z B M D 2011
11 F 60 U Y G S 2010
11 F 60 X Y T O 2009
;
run;

I wish to select firstly, all IDs which occurs less than 5 times with corresponding variables in another dataset(newly created). After that I wish to select randomly from the list of the ids which occurs more than 5 times 5 ids with corresponding variables.

A row should not be selected twice. If already selected it should be flagged so that. it wouldn't be selected again.

Any help?

Re: selecting IDs randomly from a dataset

Tom — Fri, 30 Jul 2021 15:39:06 GMT

So you want to stratify your sample based on number of times that they appear?

You can use PROC FREQ (or PROC SQL) to count the number of observations per ID.

proc freq data=test;
  tables id / noprint out=count;
run;

Do you just want to sample from the unique ID list?

Or do you want to sample observations from the original file?

Show an example of the output you want for the given example input.

Re: selecting IDs randomly from a dataset

FreelanceReinh — Fri, 30 Jul 2021 15:40:28 GMT

Hello @Anita_n,

@Anita_n wrote:

I wish to select firstly, all IDs which occurs less than 5 times with corresponding variables in another dataset(newly created). After that I wish to select randomly from the list of the ids which occurs more than 5 times 5 ids with corresponding variables.

I guess you mean 5 observations, not 5 IDs, from those IDs with more than 5 observations and also that you want all 5 observations from those IDs with exactly 5 observations (if there were any). In this case PROC SURVEYSELECT with the SELECTALL option (and the selection method "simple random sampling," which is the default) meets the requirements:

proc sort data=test;
by pat_id;
run;

proc surveyselect data=test
method=srs n=5 selectall /* outall */
seed=2718 out=want(drop=SelectionProb SamplingWeight);
strata pat_id;
run;

Use the OUTALL option (commented out above) if you want all observations from TEST in dataset WANT with a 0-1 flag variable (named Selected) indicating whether or not an observation belongs to the random sample. Otherwise, WANT contains only the random sample.

Re: selecting IDs randomly from a dataset

Anita_n — Fri, 30 Jul 2021 15:55:51 GMT

@FreelanceReinh: Thanks, that is exactly what I wanted