topic Re: Computation of backward moving percentiles in SAS Procedures

Computation of backward moving percentiles

EsbenVibel — Tue, 09 Jul 2013 19:08:14 GMT

Hello everybody,

I work with a time series dataset, and I need to compute a backward moving percentile for a time series. How can this be done in SAS? I have considered the EXPAND procedure, but to my knowledge this procedure can only compute a backward moving median (i.e. 50% percentile) using the "MOVMED" statement. How should I proceed if I want to compute a (for example) 20% backward moving percentile using a time window of, say, 250 observations?

Thanks in advance!

Best,

Esben Vibel

Re: Computation of backward moving percentiles

Ksharp — Wed, 10 Jul 2013 01:05:42 GMT

How many obs you need to backward moving ?

Re: Computation of backward moving percentiles

EsbenVibel — Wed, 10 Jul 2013 05:27:43 GMT

My dataset has approx. 10,000 obs., and I would like to compute 20% backward moving percentiles based on a window of 252 observations.

Best,

Esben

Re: Computation of backward moving percentiles

Ksharp — Wed, 10 Jul 2013 06:56:51 GMT

I am not familiar with proc expand, maybe you can check the documention and find some one option.

And my code make a window of 252 includes the current obs.

data have(drop=i);
do i=1 to 10000;
 x=ranuni(-1);
 output;
 end;
run;
data want;
 set have;
 array a{0:251} _temporary_ ;
 a{mod(_n_,252)}=x;
 pct_20=pctl(20,of a{*});
run;

Ksharp

Re: Computation of backward moving percentiles

EsbenVibel — Wed, 10 Jul 2013 07:20:43 GMT

When I run the last data step, the log writes the following error message:

ERROR: The ARRAYNAME

specification requires a variable based array

The error message refers to the last line (i.e. pct_20=pctl(20,of a{*});). Should this be changed somehow?

Esben

Re: Computation of backward moving percentiles

Ksharp — Wed, 10 Jul 2013 07:30:06 GMT

I have no problem. did you lost _temporary_ ?

Re: Computation of backward moving percentiles

EsbenVibel — Wed, 10 Jul 2013 07:35:13 GMT

I simply copied your code directly into SAS and ran it. I use SAS 9.1; do I need newer version to run the code?

Esben

Re: Computation of backward moving percentiles

Ksharp — Wed, 10 Jul 2013 11:33:49 GMT

Are you still using sas 9.1?

 

data have(drop=i);
do i=1 to 10000;
 x=ranuni(-1);
 output;
 end;
run;
data want(drop=aa:);
 set have;
 array a{0:251} aa1-aa252 ;
 retain aa: ;
 a{mod(_n_,252)}=x;
 pct_20=pctl(20,of a{*});
run;

Ksharp

Re: Computation of backward moving percentiles

EsbenVibel — Thu, 11 Jul 2013 09:43:00 GMT

Thanks a lot! It works perfectly.