reading next observation's value in current observation

Question

I've a dataset called 'input' with the following observations

ID Salary
10 1000
20 2000
30 3000
40 4000

I need an output dataset with following observations

ID Salary Next_row_Salary
10 1000 2000
20 2000 3000
30 3000 4000
40 4000 null

Note: The scenario is next obersavtion's salary should be the current observation's value for the column Next_Row_salary. If there is no next observation then the current observation's value for the column Next_Row_salary should be 'null'.

Kindly help me out in creating a sas code for this scenario.

Answer 1

There are a few ways to achieve this, here's how I would do it.

data have;
   input ID Salary;
   cards;
10 1000
20 2000
30 3000
40 4000
;
run;

data want;
   recno=_n_+1;
   set have end=last;
   if not last 
           then set have (keep=salary rename=(salary=next_row_salary)) point=recno;
      else call missing(next_row_salary);
run;

Answer 2

There's no direct way to do this in a data step. There's two approaches you can use:

Option 1: Sort in reverse, use the lag function

proc sort data=your_dataset;
 by descending id;
run;

data your_dataset;
 set your_dataset;
 next_row_salary = lag(salary);
run;

proc sort; by id; run;

Options 2: Use proc expand

proc expand data=your_dataset method=none;
 by id;
 convert salary = next_row_salary / transformout=(lead 1);
run;

Answer 3

This code is from Paul Dorfman on SAS-L and it does what you are looking for as well with one pass through the data

Data Salary;
input id salary;
Datalines;
10 1000
20 2000
30 3000
40 4000
;
Run;

data need ;
retain id salary;
set salary (rename=(id = origid salary=next_salary)) end=end ;
if _n_ > 1 then output;
salary = next_salary;
id = origid;
if not end then return;
call missing(next_salary);
output;
drop origid;
run ;