Identifying the variable associated with the first.date for a series of dates

[cschmidt]

Hello,

I would like to identify the first occurrence of an intervention for 4 different interventions. In other words, of the 4 interventions which one occurred first. I have included sample variables and code. thanks!

sample data set:

patient1   intervention1  int1_date  intervention2  int2_date  intervention3  int3_date  intervention4  int4_date

patient2  ............

data test2;

set test;

by ID;

if (int1_date < int2_date and int1_date < int3_date and int1_date < int4_date) then int =1;

if (int2_date < int1_date and int2_date < int3_date and int2_date < int4_date) then int =2;

if (int3_date < int1_date and int3_date <int2_date and int3_date < int4_date) then int =3;

if (int4_date< int1_date and int4_date <int2_date and int4_date < int3_date) then int =5;

else int = 5;

run;

[Kurt_Bremser]

Transpose to a long dataset, sort by patient and date, and then extract the information at first.patient from _name_.

Maxim 19: Long Beats Wide.

[cschmidt]

Thank you

[Reeza]

Arrays, and WHICHN() are the key items here.

data test2;
set test1;

array _dates(*) int1_date int2_date ....;
array _ints(*) intervention1-intervention4;

*find the minimum date - ignores missing;
min_date = min(of _dates(*));

*what about ties - find index of lowest date;
index_min_date = whichn(min_date, of _dates(*));

*get relevant intervention based on index;
first_intervention = _ints(index_min_date);

run;

Here's a tutorial on using Arrays in SAS
https://stats.idre.ucla.edu/sas/seminars/sas-arrays/

---

@cschmidt wrote:

Hello,

I would like to identify the first occurrence of an intervention for 4 different interventions. In other words, of the 4 interventions which one occurred first. I have included sample variables and code. thanks!

sample data set:

patient1   intervention1  int1_date  intervention2  int2_date  intervention3  int3_date  intervention4  int4_date

patient2  ............

data test2;

set test;

by ID;

if (int1_date < int2_date and int1_date < int3_date and int1_date < int4_date) then int =1;

if (int2_date < int1_date and int2_date < int3_date and int2_date < int4_date) then int =2;

if (int3_date < int1_date and int3_date <int2_date and int3_date < int4_date) then int =3;

if (int4_date< int1_date and int4_date <int2_date and int4_date < int3_date) then int =5;

else int = 5;

run;

---

[mkeintz]

One could use your approach but much more simply:

data test2;
  set test;
  if int_date1=min(of int_date:) then int=1; else
  if int_date2=min(of int_date:) then int=2; else
  if int_date3=min(of int_date:) then int=3; else
  if int_date4=min(of int_date:) then int=4;
run;

Or more generally:

data test2;
  set test;
  int=whichn(min(of int_datet:),of min_date:);
run;

The latter assumes your variables are named, int_date1, int_date2, ... int_date4, in that order.

The nice thing about the latter is that it accommodates any number of consecutively named INT_DATE variables.

One issue, for both techniques.  If there is a tie for minimum(earliest) date, then this always chooses the leftmost.

[cschmidt]

Thank you!