topic selecting a specific sequence of records in SAS Procedures

selecting a specific sequence of records

lnb001 — Wed, 26 Oct 2011 14:40:54 GMT

I am trying to select a specific sequence of records in a SAS dataset. For example, I have repeated measures data with multiple records per case ID. I am trying to select 3 records where variable 2 is flanked by 2 instances of variable 1. So for record 1, variable 1 would be true, then at record 2 variable 2 would be true, and at record 3 variable 1 would again be true. The variable in question is a lab value where I am looking for instances where the lab value is low, then changes to high, then changes back to low. Each case ID could have more than 3 records, but I only want to pick out the records where this low-high-low instance occurs. Anything before or after that instance doesn't matter. If multiple instances occur for the same ID I would like to keep those as well. Is this possible?

selecting a specific sequence of records

art297 — Wed, 26 Oct 2011 14:47:38 GMT

The method described at http://www.sascommunity.org/wiki/Look-Ahead_and_Look-Back may be perfect for what you are trying to do.

Re: selecting a specific sequence of records

Peter_C — Wed, 26 Oct 2011 15:08:29 GMT

double pass within Case_ID

collecting info on the condition
extracting if rules require it.

there will be no measurable performance penalty when your data are in case_ID order

For example

data wanted ;

set labValues( in= pass1) labValues(in=pass2) ;

by case_ID ;

if pass2 then do ;

if wanted then output ;

delete ;

end ;

if first.case_ID then do ;

wanted = 0 ;

abc = '000' ;

end ;

if wanted then delete ;

if 1<= value <= 2 then abc = cats( value, abc ) ;

else abc= cats( '0', abc ) ;

if abc = '121' then wanted = 1 ;

drop abc wanted ;

retain abc wanted ;

run ;

Message was edited by: Peter Crawford

also needed the RETAIN statement

selecting a specific sequence of records

lnb001 — Wed, 26 Oct 2011 15:50:32 GMT

This solution seems to have worked for picking out the records with the high (middle) value. I am now trying to keep the records that flank this middle value (the lows). Any idea how I could do this? Thanks.

Re: selecting a specific sequence of records

art297 — Wed, 26 Oct 2011 18:05:45 GMT

I think it would help if you provide some example data. If the look-ahead-look-back method worked you could just output all three records at the same time since you have them in memory already. The only issue I can forsee is that flanking records might be part of yet another set and I don't know if you would only want them represented once.

Re: selecting a specific sequence of records

lnb001 — Mon, 31 Oct 2011 14:34:00 GMT

Bear with me as I try to create some sample data:

Case ID X High Low

0000001: 50 . 1

0000001: 672 1 .

0000001: 50 . 1

0000002: 50 . 1

0000002: 100 1 .

0000002: 50 . 1

In the example above, I have successfully assigned a value to the Records where X is > 50 and <=50. This is indicated by the newly created High and Low fields. While it is easy to select the High values, what I want is to select the High as well as the two Lows that flank it (e.g. the first three records of each Case ID). This is tricky for me since there are obviously records that have a Low value w/o a High, and records with High values and no Lows. Does this make sense?

Re: selecting a specific sequence of records

Peter_C — Mon, 31 Oct 2011 14:58:29 GMT

for Case_id=2 do you want all rows (rows 4-8), or only the three (rows 4-6 in that example) surrounding the "High"?

Re: selecting a specific sequence of records

art297 — Mon, 31 Oct 2011 14:59:25 GMT

I'm still not sure if I understand what you are trying to accomplish. The following finds a record that has a value greater than 50 and outputs it. If there is a record that precedes it, it then outputs it and then outputs the record (if there is one) that comes aftre it. Is it at least close to what you are trying to do?

data have;

input Case_ID $ X;

cards;

0000001 50

0000001 672

0000001 49

0000002 42

0000002 100

0000002 37

0000002 50

;

data want;

set have;

if x gt 50 then highlow=1;

else highlow=0;

run;

data want;

set have;

by Case_ID;

set have ( firstobs = 2 keep = x rename = (x = Next_x) )

have ( obs = 1 drop = _all_ );

Prev_x = ifn( first.Case_ID, (.), lag(x) );

Next_x = ifn( last.Case_ID, (.), Next_x );

if x gt 50 then do;

output;

if not first.Case_ID then do;

x=Prev_x;

output;

end;

if not last.Case_ID then do;

x=Next_x;

output;

end;

run;

Re: selecting a specific sequence of records

lnb001 — Mon, 31 Oct 2011 15:14:25 GMT

Just records 4-6.

selecting a specific sequence of records

Peter_C — Mon, 31 Oct 2011 15:25:50 GMT

when the data are like

0000001: 50 . 1

0000001: 672 1 .

0000001: 50 . 1

0000001: 672 1 .

0000001: 50 . 1

should row 3 appear twice (once for each of the overlapping trios) or just once?

selecting a specific sequence of records

lnb001 — Mon, 31 Oct 2011 15:58:36 GMT

In my example above, this is data I am left with after I assign values to an existing data set. As I mentioned, I am left with Case IDs that have a High flanked by two lows. I am also left with Case IDs that have Highs and Lows but no actual Highs that have the flanking.

I want to create a new data set that shows only the records where the flanking occurs. To be more clear, maybe I should have written the sample data as follows:

Case ID Date X High Low

0000001 01/01/2010 50 . 1

0000001 02/01/2010 672 1 .

0000001 03/01/2010 50 . 1

0000002 01/01/2011 50 . 1

0000002 02/01/2011 100 1 .

0000002 03/01/2011 50 . 1

0000002 04/01/2011 50 . 1

0000002 05/01/2011 50 . 1

In this example, I want to keep all Case 0000001 records, and only the Case 0000002 records dated 01/01/2011, 02/01/2011, and 03/01/2011 because the remaining records (04/01/2011 & 05/01/2011) do not have the High flanked by two Lows.

So the new dataset would look like:

Case ID Date X High Low

0000001 01/01/2010 50 . 1

0000001 02/01/2010 672 1 .

0000001 03/01/2010 50 . 1

0000002 01/01/2011 50 . 1

0000002 02/01/2011 100 1 .

0000002 03/01/2011 50 . 1

selecting a specific sequence of records

art297 — Mon, 31 Oct 2011 16:11:54 GMT

You didn't indicate whether you had tried my suggested code. Given your new additional requirements, I would suggest that you try the following and see if it does what you want:

data have;

input Case_ID Date mmddyy10. X;

cards;

0000001 01/01/2010 50

0000001 02/01/2010 672

0000001 03/01/2010 50

0000002 01/01/2011 50

0000002 02/01/2011 100

0000002 03/01/2011 50

0000002 04/01/2011 50

0000002 05/01/2011 50

;

data want;

set have;

by Case_ID;

set have ( firstobs = 2 keep = x date rename =

(x = Next_x date = Next_date) )

have ( obs = 1 drop = _all_ );

Prev_x = ifn( first.Case_ID, (.), lag(x) );

Prev_date = ifn( first.Case_ID, (.), lag(date) );

Next_x = ifn( last.Case_ID, (.), Next_x );

Next_date = ifn( last.Case_ID, (.), Next_date );

if x gt 50 and not (first.Case_ID or last.Case_ID)

then do;

output;

x=Prev_x;

date=Prev_date;

output;

x=Next_x;

date=Next_date;

output;

end;

run;

proc sort data=want;

by case_ID date;

run;

Re: selecting a specific sequence of records

MikeZdeb — Mon, 31 Oct 2011 16:21:07 GMT

Hi ... another approach with your data that gives your desired result ...

data x;

input id dt : mmddyy. x high low;

format id z7. dt mmddyy10.;

datalines;

0000001 01/01/2010 50 . 1

0000001 02/01/2010 672 1 .

0000001 03/01/2010 50 . 1

0000002 01/01/2011 50 . 1

0000002 02/01/2011 100 1 .

0000002 03/01/2011 50 . 1

0000002 04/01/2011 50 . 1

0000002 05/01/2011 50 . 1

;

run;

data q;

set x;

by id;

if not (first.id or last.id);

pre = _n_ - 1;

post = _n_ + 1;

set x (keep=x rename=(x=x0)) point=pre;

set x (keep=x rename=(x=x1)) point=post;

if x gt x0 and x gt x1 then do;

set x point=pre; output;

set x point=_n_; output;

set x point=post; output;

end;

drop x0 x1;

run;

Re: selecting a specific sequence of records

lnb001 — Mon, 31 Oct 2011 19:09:46 GMT

With some tweaking I think I have made this work. Thanks all for the input.

Re: selecting a specific sequence of records

Ksharp — Tue, 01 Nov 2011 04:54:11 GMT

data x;
input id dt : mmddyy. x high low;
format id z7. dt mmddyy10.;
datalines;
0000001    01/01/2010              50       .             1
0000001    02/01/2010              672     1            .
0000001    03/01/2010              50       .             1
0000002    01/01/2011              50       .             1
0000002    02/01/2011              100     1            .
0000002    03/01/2011              50       .             1
0000002    04/01/2011              50       .             1
0000002    05/01/2011              50       .             1
;
run;
data want(drop=count);
 set x;
 count+1;
 if low=1 and (id=lag(id) and lag(high)=1) and (id=lag2(id) and lag2(low)=1) then do;
  output;
  _count=count-1;set x point=_count;output;
  _count=count-2;set x point=_count;output;
  end;
run;

Ksharp

Re: selecting a specific sequence of records

lnb001 — Wed, 02 Nov 2011 19:27:43 GMT

Now that I have figured how to keep these three records, I am told I need to transpose the data. I start with this:

Case ID Date X High Low

0000001 01/01/2010 50 . 1

0000001 02/01/2010 672 1 .

0000001 03/01/2010 50 . 1

0000002 01/01/2011 50 . 1

0000002 02/01/2011 100 1 .

0000002 03/01/2011 50 . 1

But am told I need to end up with this:

Case ID Date 1 Date 2 Date 3

000001 01/01/2010 02/01/2010 03/01/2010

000002 01/01/2011 02/01/2011 03/01/2011

Obviously proc transpose would do this easily if I only had one 'trio' for each Case ID. In some cases, however, there are multiple 'trios':

Case ID Date X High Low

0000003 01/01/2010 50 . 1

0000003 02/01/2010 672 1 .

0000003 03/01/2010 50 . 1

0000003 04/01/2010 50 . 1

0000003 05/01/2010 999 1 .

0000003 06/01/2010 50 . 1

0000004 01/01/2011 50 . 1

0000004 02/01/2011 100 1 .

0000004 03/01/2011 50 . 1

0000004 04/01/2011 50 . 1

0000004 05/01/2011 300 1 .

0000004 06/01/2011 50 . 1

In this instance, I would want my new table to look like:

Case ID Date 1 Date 2 Date 3

000003 01/01/2010 02/01/2010 03/01/2010

000003 04/01/2010 05/01/2010 06/01/2010

000004 01/01/2011 02/01/2011 03/01/2011

000004 04/01/2011 05/01/2011 06/01/2011

How can I do this?

Re: selecting a specific sequence of records

Ksharp — Thu, 03 Nov 2011 03:39:13 GMT

It is easy.IF you make sure there are three observations in each group.

data x;
input id dt : mmddyy. x high low;
format id z7. dt mmddyy10.;
datalines;
0000003    01/01/2010              50       .             1
0000003    02/01/2010              672     1            .
0000003    03/01/2010              50       .             1
0000003    04/01/2010              50       .             1
0000003    05/01/2010              999     1            .
0000003    06/01/2010              50       .             1
0000004    01/01/2011              50       .             1
0000004    02/01/2011              100     1            .
0000004    03/01/2011              50       .             1
0000004    04/01/2011              50       .             1
0000004    05/01/2011              300     1            .
0000004    06/01/2011              50       .             1
;
run;
data x;
 set x;
 if mod(_n_,3)=1 then do;count=0;group+1;end;
 count+1;
run;
proc transpose data=x out=want(drop=group _name_) prefix=date;
 by id group;
 var dt;
 id count;
run;

Ksharp

Re: selecting a specific sequence of records

lnb001 — Thu, 03 Nov 2011 11:36:36 GMT

Thanks. This seems to be a step in the right direction, BUT I am left with this when I try to transpose the data:

Case ID Date Date1 Date2 Date3

0000003 01/01/2010 01/01/2010 . .

0000003 02/01/2010 . 02/01/2010 .

0000003 03/01/2010 . . 03/01/2010

0000003 04/01/2010 04/01/2010 . .

0000003 05/01/2010 . 05/01/2010 .

0000003 06/01/2010 . . 06/01/2010

0000004 01/01/2011 01/01/2011 . .

0000004 02/01/2011 . 02/01/2011 .

0000004 03/01/2011 . . 03/01/2011

0000004 04/01/2011 04/01/2011 . .

0000004 05/01/2011 . 05/01/2011 .

0000004 06/01/2011 . . 06/01/2011

Re: selecting a specific sequence of records

art297 — Thu, 03 Nov 2011 12:43:42 GMT

That definitely ISN'T the result I get when I run KSharp's code. You must have changed something.

Re: selecting a specific sequence of records

lnb001 — Thu, 03 Nov 2011 13:52:19 GMT

You're right, I referenced the wrong variable in my 'by' statement. I think I have what I want now. Thank you all.