dates subtraction

[radhikaa4]

Following table - i would like to subtract randdate and start date and convert into "Day" but if randdate = startdate then i want that time to be Day 1, rather than day 0

subjectid	startdate	randdate
1	1/1/2019	1/1/2019
1	1/2/2019	1/1/2019
1	1/3/2019	1/1/2019
1	1/4/2019	1/1/2019

Something like this

subjectid	startdate	randdate	group
1	1/1/2019	1/1/2019	Day 1
1	1/2/2019	1/1/2019	Day 2
1	1/2/2019	1/1/2019	Day 2
1	1/3/2019	1/1/2019	Day 3

Right now i can only do randdate - startdate and recode if subtract=0 then group = "day 1" but this is tedious

[PaigeMiller]

Is startdate a numeric variable or a character variable?

Is randdate a numeric variable or a character variable?

[ed_sas_member]

Hi @radhikaa4 

The solution you described is the easiest.

You can also define your own function using proc fmcp. It is easier to maintain if the rule is going to change in the future and if you use it in multiple datasets.

/* Function definition -> Fcalc_Day() with 2 arguments as defined below */

libname lib_fcmp "&path."; /* to be specified */

proc fcmp outlib=lib_fcmp.functions.dev;
	function Fcalc_Day(randdate, startdate);
	
	if randdate > startdate then return (startdate - randdate);
	if randdate <= startdate then return (startdate - randdate + 1);
	
	endsub;
quit;

options cmplib=lib_fcmp.functions;

/* Use case */
data have;
	input subjectid	startdate : mmddyy10. randdate : mmddyy10.;
	format startdate randdate mmddyy10.;
	cards;
1 12/31/2018 1/1/2019
1 1/1/2019 1/1/2019
1 1/2/2019 1/1/2019
1 1/3/2019 1/1/2019
1 1/4/2019 1/1/2019
;
run;

data want;
	set have;
	day = Fcalc_Day(randdate,startdate);
run;

[Astounding · Accepted solution]

The "tedious" way is fine, but you can see if you find this more appealing:

days = startdate - randdate + (startdate >= randdate);