Previous or Current recorded height

[SASPhile]

patient      height        weight       visit_date        BMI

1001            5                 130      2012-01-05     130(5*5) 

1001                               145      2012-06-01     145(5*5)

1001            5.2             148      2013-01-02     148(5.2*5.2)

1002           5.1              130      2012-01-05   130(5.1*5.1) 

1002                               145      2012-06-01   145(5.1*5.1)

1002                               148      2013-01-02   148(5.1*5.1)

1003                              130      2012-01-05     

1003           5.3                          2012-06-01   

1003                               148      2013-01-02     148(5.3*5.3)

1004                              130      2012-01-05     

1004                                           2012-06-01   

1004                               148      2013-01-02    

1004             5.5                           2013-01-02   

If weight is null no BMI

If height is null, take height from earliest record

How to get BMI's for patients the following way?

For patient 1001 the BMI in second record is calculated by taking height from previous visit.

For 1002  the BMi is recorded from height in first record

For 1003 height is from second record.

For 1004 NO BMI

[error_prone]

Please post the data as data step and show the code you have already.

Idea: use a hash object.

[SASPhile]

data testdata;
input patient $1-4 height $16-20 weight $34-37 date $43-53 BMI $58-70;
cards;
1001            5                130      2012-01-05     130(5*5)  
1001                             145      2012-06-01     145(5*5)
1001            5.2              148      2013-01-02     148(5.2*5.2)
1002           5.1               130      2012-01-05     130(5.1*5.1)  
1002                             145      2012-06-01     145(5.1*5.1)
1002                             148      2013-01-02     148(5.1*5.1)
1003                              130     2012-01-05      
1003           5.3                        2012-06-01    
1003                              148     2013-01-02     148(5.3*5.3)
1004                              130     2012-01-05      
1004                                      2012-06-01    
1004                              148     2013-01-02     
1004             5.5                      2013-01-02    
;
run;

data t2;
 set testdata;
 by patient date;
 retain new_ht;
 if first.patient and height ne '' then new_ht=height;
 run;

[ballardw]

BMI usually uses weight in kg/(height in m squared)

I doubt if your 5 for height is in meters and the weights look more likely to be pounds as well.

[ShiroAmada]

Try this...

Build a lookup table where height is not missing with the earliest date.  The data step merge will populate height (only when missing).

proc sql;
  create table hgt as
  select patient, height, visit_date from HAVE 
where height is not missing
group by patient
having min(visit_dt)=visit_dt;
quit;

proc sort data=have;
  by id;
proc sort data=hgt;
  by id;
run;

data want;
  merge have(in=a) hgt(in=b rename=(height=heightb));
  by id;
  if a;
  if height=. then height=heightb;
  drop heightb;
run;

Hope this helps.