Creating a do loop that subtracts from column to column

[Mando]

I am new to SPSS and I am trying to figure out how mix a do-loop with an array to do the following:

write a SAS code using SAS data step only and “do loop” so that you can modify the above data set to get a new data set having 21 variables (X1-X21) which will look like below:

X1       X2       X3           …                X21    

 1          .           .                                   .          

 2          1          .                                   .

 3          2          1                                  .

 21        19        18                                1

The data set used is the following:

data example;
input X;
datalines;
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
;
RUN;

I am trying to figure out the shortest way to get the proper output and if someone could help me out and give me some tips I would be very greatful.

[maguiremq]

There are users on here that are much, much better at DO loops compared to me. This is my best shot, and I'm certain there is a better method.

data example;
input X;
datalines;
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
;
RUN;

data want;
	set example;
	array _x [*] 3. x1 - x21;
	do i = 1 to dim(_x);
		if i = 1 then do;
			_x[i] = x;
		end;
		else do;
			_x[i] = lag(_x[i-1]);
		end;
	end;
run;

I think there might be a typo in your 'want' data set, or I did something wrong.

X x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 x11 x12 x13 x14 x15 x16 x17 x18 x19 x20 x21 
1 1 . . . . . . . . . . . . . . . . . . . . 
2 2 1 . . . . . . . . . . . . . . . . . . . 
3 3 2 1 . . . . . . . . . . . . . . . . . . 
4 4 3 2 1 . . . . . . . . . . . . . . . . . 
5 5 4 3 2 1 . . . . . . . . . . . . . . . . 
6 6 5 4 3 2 1 . . . . . . . . . . . . . . . 
7 7 6 5 4 3 2 1 . . . . . . . . . . . . . . 
8 8 7 6 5 4 3 2 1 . . . . . . . . . . . . . 
9 9 8 7 6 5 4 3 2 1 . . . . . . . . . . . . 
10 10 9 8 7 6 5 4 3 2 1 . . . . . . . . . . . 
11 11 10 9 8 7 6 5 4 3 2 1 . . . . . . . . . . 
12 12 11 10 9 8 7 6 5 4 3 2 1 . . . . . . . . . 
13 13 12 11 10 9 8 7 6 5 4 3 2 1 . . . . . . . . 
14 14 13 12 11 10 9 8 7 6 5 4 3 2 1 . . . . . . . 
15 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 . . . . . . 
16 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 . . . . . 
17 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 . . . . 
18 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 . . . 
19 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 . . 
20 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 . 

 Wanted to add that there are better ways to do this. If you're being forced to use a DO loop for it, I'd assume it's an assignment.

Never used it personally, but I think (after seeing other posts suggesting it) that PROC EXPAND would be a good fit here.

https://documentation.sas.com/doc/en/pgmsascdc/9.4_3.3/etsug/etsug_expand_syntax02.htm

[PaigeMiller]

What is being subtracted here (from column to column)?

Is this is a more general problem where the data can be any numbers, or does it apply only to data which is consecutive integers (in which case no subtraction is needed)?