I need help getting a difference between subsequent values on a list

[Xamius32]

So I need to see how many days have passed between observations.

So :

Person Date

A 1/1/12

A  1/5/12

A  1/7/12

B 4/5/12

B 4/9/12

B and so on

B

B

C

C

Basically, I want a column to the right that says X days have passed since last instance. I am thinking an array, but I am horrible at arrays.

[data_null__ · Accepted solution]

DIF function sounds about right.

data dif;
   input id:$1. date :mmddyy.;
   format date date.;
   cards;
A 1/1/12
A  1/5/12
A  1/7/12
B 4/5/12
B 4/9/12
;;;;
   run;
data dif2;
   set dif;
   by id;
   dif = dif(date);
   if first.id then dif=.F;
   run;