SAS Rolling conditional statement (similar to excel) - sas

Question

I have a dataset and I would like to create a rolling conditional statement row by row (not sure what the exact term is called in SAS). I know how to do it in Excel but not sure on how it can be executed on SAS. The following is the dataset and what I would like to achieve.
Data set
----A---- | --Date-- | Amount |
11111 Jan 2015 1
11111 Feb 2015 1
11111 Mar 2015 2
11111 Apr 2015 2
11111 May 2015 2
11111 Jun 2015 1
11112 Jan 2015 2
11112 Feb 2015 1
11112 Mar 2015 1
11112 Apr 2015 4
11112 May 2015 3
11112 Jun 2015 1
I would like to 2 columns by the name of 'X' and 'Frequency' which would provide for each Column 'A' and 'Date' whether the Amount has gone up or down and by how much. See sample output below.
----A---- | --Date-- | Amount | --X-- | Frequency |
11111 Jan 2015 1 0 0
11111 Feb 2015 1 0 0
11111 Mar 2015 2 Add 1
11111 Apr 2015 2 0 0
11111 May 2015 2 0 0
11111 Jun 2015 1 Drop 1
11112 Jan 2015 2 0 0
11112 Feb 2015 1 Drop 1
11112 Mar 2015 1 0 0
11112 Apr 2015 4 Add 3
11112 May 2015 3 Drop 1
11112 Jun 2015 1 Drop 2

Answer 1

Example using Lag1():
Data A;
input date monyy7. Y $;
datalines;
Jan2015 1
Feb2015 1
Mar2015 2
Apr2015 2
May2015 2
Jun2015 1
Jan2015 2
Feb2015 1
Mar2015 1
Apr2015 4
May2015 3
Jun2015 1
;
data B;
set A;
lag_y=lag1(Y);
if lag_y = . then X ='missing';
if Y = lag_y then X='zero';
if Y > lag_y and lag_y ^= . then x='add';
if Y < lag_y then x= 'drop';
freq= abs(Y-lag_y);
run;
Output:
Obs date Y lag_y X freq
1 20089 1 missing
2 20120 1 1 zero 0
3 20148 2 1 add 1
4 20179 2 2 zero 0
5 20209 2 2 zero 0
6 20240 1 2 drop 1
7 20089 2 1 add 1
8 20120 1 2 drop 1
9 20148 1 1 zero 0
10 20179 4 1 add 3
11 20209 3 4 drop 1
12 20240 1 3 drop 2