Many-to-one association

[Altal]

Hi All,

Is there a simple way (datastep or sql) to associate multiple observations in a dataset with specific time points to an earlier time point in a one-per-id dataset, as long as the observation falls inbetween time point of interest? an example may explain it better...

I have a dataset with visits dates; and I have treatments with treatment dates. I'd like to associate each trt to the visit earlier as long as the trt was given in the period between the two consecutive visits...

data visits;

input visit $ visitdt mmddyy8.;

format visitdt mmddyy8.;

cards;

1 11/12/12

2 03/02/13

3 04/15/13

4 06/16/13

;

run;

data trt;

input trt $ trtDt mmddyy8.;

format trtDt mmddyy8.;

cards;

A 11/20/12

A 11/29/12

B 12/02/12

A 03/01/13

B 04/15/13

A 04/16/13

B 06/17/13

A 08/15/13

;

run;

I'm interested to this structure...

Visit       visitdt                    trt           trtDt

1              11/12/12              A             11/20/12

1              11/12/12              A             11/29/12

1              11/12/12              B             12/02/12

1              11/12/12              A             03/01/13

2              03/02/13                              .

3              04/15/13              B             04/15/13

3              04/15/13              A             04/16/13

4              06/16/13              B             06/17/13

4              06/16/13              A             08/15/13

Any help is appreciated... thanks!

[art297 · Accepted solution]

There are probably numerous ways.  Here is one:

data visits;

  set visits;

  set visits(firstobs=2 keep=visitdt rename=(visitdt=next_visitdt))

      visits(firstobs=1 drop=_all_);

  if missing(next_visitdt) then next_visitdt='31dec9999'd;

run;

proc sql;

  create table want as

    select *

      from visits left join trt

        on visitdt<=trtdt<next_visitdt

          order by visitdt,trtdt

  ;

quit;

[Altal]

Thanks very much!