Computing percent change between different years with various companies:

[jap6198]

Hello,

I am trying to calculate the percent change in Assets_Total between year 2018-2019 over various companies. Please help! 

example: 

Permno	Company	Date	Assets_Total
111	xx	1/2/18	1
111	xx	1/2/19	2
222	yy	1/2/18	3
222	yy	1/2/19	4
333	zz	1/2/18	5
333	zz	1/2/19	6

what I want: 

Permno	Company	Date	Assets_Total	pcnt change
111	xx	1/2/18	1	-
111	xx	1/2/19	2	1
222	yy	1/2/18	3	-
222	yy	1/2/19	4	0.33333333
333	zz	1/2/18	5	-
333	zz	1/2/19	6	0.2

THANK YOU!!! 

@PaigeMiller

[mkeintz]

data want;
  set have;
  by permno;
  pctn_change=dif(assets_total)/lag(assets_total);
  if first.permno then pctn_change=.;
run;

The DIF function is defined as  DIF(x) ==   x-LAG(x).

The SET with a BY statement provides a dummy to identify when the record in hand is the start (first.permno) or end (last.permno) of a sequence of records with the same permno.  So the IF statement sets pctn_change to missing to prevent contamination from the prior permno.