Differences for continuous columns

[HN2001]

I have a dataset that looks like that following.  I am trying to find the best way to calculate the increase across days (DIFDay2-Day1, DIFDay3-Day2, DIFDay4-Day3)  My data going forward will have more days included so I'm hoping I don't have to list out each day.  Would an array be best here?

Group	Day1	Day2	Day3	Day4	DIFDay2 - Day1	DIFDay3 - Day2	DIFDay4 - Day3
G1	2639	2639	2645	2671
G2	3079	3503	3554	3620
G3	285	291	358	379
G4	9434	9510	9570	9690
G5	13182	13525	13548	13902

[SASJedi · Accepted solution]

Here's a good start:

data have;
input Group:$2	Day1	Day2	Day3	Day4;
datalines;
G1	2639	2639	2645	2671
G2	3079	3503	3554	3620
G3	285	291	358	379
G4	9434	9510	9570	9690
G5	13182	13525	13548	13902
;

proc sql noprint;
select count(*) into :dim
   from dictionary.columns 
   where libname="WORK" and memname="HAVE"
     and name like "Day%"
;

data want;
  set have;
  array Day[*] Day:;
  array DiffDay[&dim];
  do i=2 to dim(DiffDay);
     DiffDay[i]=Day[i]-Day[i-1];
  end;
  drop i DiffDay1;
run;

Result:

Group	Day1	Day2	Day3	Day4	DiffDay2	DiffDay3	DiffDay4
1	2639	2639	2645	2671	0	6	26
2	3079	3503	3554	3620	424	51	66
3	285	291	358	379	6	67	21
4	9434	9510	9570	9690	76	60	120
5	13182	13525	13548	13902	343	23	354

[HN2001]

Thank you very much!

[data_null__]

I'm on a PROC SCORE kick.  You need a custom SCORE data set like this.

Which you can generate with iterative DO.

data have;
   infile cards expandtabs;
   input Group:$2. Day1-Day4;
   datalines;
G1	2639	2639	2645	2671
G2	3079	3503	3554	3620
G3	285	291	358	379
G4	9434	9510	9570	9690
G5	13182	13525	13548	13902
;;;;
   run;
data score;
   if 0 then set have(keep=Day:);
   array v[*] _numeric_;
   retain _TYPE_ 'SCORE';
   length _name_ $32;
   do i = 1 to dim(v);
      call missing(of v[*]);
      v[i]=-1; 
      do j = i+1 to dim(v);
         _name_ = catx('_',vname(v[i]),vname(v[j]));
         v[j] = 1;
         output;
         v[j] = .;
         end;
      end;
   drop i j;
   stop;
   run;
proc print;
   run;
proc score data=have score=score out=diffs;
   id group day:;
   var day:;
   run;
proc print;
   run;

And SCORE using PROC SCORE.