SAS Change the first record - sas

Question

Let's imagine the following table ...
obs
State
Imp
i
i2
1
me
100
100
2
me
90
100
100
3
me
80
100
100
4
me
70
100
100
5
me
1000
1000
100
6
me
900
1000
1000
7
me
800
1000
1000
8
me
0
1000
1000
9
me
2000
2000
1000
10
me
1900
2000
2000
11
gu
20
2000
2000
12
ca
40
2000
2000
13
ca
50
2000
2000
14
ca
30
2000
2000
15
ca
10
2000
2000
as you can see column "i2" is lag (i). What I want to do is:
1.- column "i" finds the maximum value as it progresses, so i want to reset that column
"i" every first "state", in order to get that maximum value of each state.
2.- modify the column "i2" so that it is as follows:
that each first value of "State" (obs 1-me, 11-gu and 12-ca) column "i" has the value
of column "imp"
obs
State
Imp
i
i2
1
me
100
100
100
2
me
90
100
100
3
me
80
100
100
4
me
70
100
100
5
me
1000
1000
100
6
me
900
1000
1000
7
me
800
1000
1000
8
me
0
1000
1000
9
me
2000
2000
1000
10
me
1900
2000
2000
11
gu
20
20
20
12
ca
40
40
40
13
ca
50
50
40
14
ca
30
50
50
15
ca
10
50
50
i have tried with this code, but it doesn't work
data metodo;
set sa80;
retain i;
if first.state then i=max(imp);
else i = max(imp,i);
i2 = lag(i);
run;
data final;
set metodo;
retain i2_aux;
if first.state then i2_aux = total;
else i2_aux = i2;
run;
Hope you could help, and thank you in advance

Answer 1

The main thing it not use an existing variable as the new RETAINed variable because then each time the SET statement executes the value retained is replaced with the value read from the input.
It also helps if the data is sorted by the key variable, although you can use the NOTSORTED keyword on the BY statement to process grouped, but not sorted, data.
data have;
input state $ imp ;
cards;
ca 40
ca 50
ca 30
ca 10
gu 20
me 100
me 90
me 80
me 70
me 1000
me 900
me 800
me 0
me 2000
me 1900
;
data want;
set have ;
by state notsorted;
retain i;
i=max(i,imp);
if first.state then i=imp;
i2=lag(i);
if first.state then i2=imp;
run;
Results:
Obs state imp i i2
1 ca 40 40 40
2 ca 50 50 40
3 ca 30 50 50
4 ca 10 50 50
5 gu 20 20 20
6 me 100 100 100
7 me 90 100 100
8 me 80 100 100
9 me 70 100 100
10 me 1000 1000 100
11 me 900 1000 1000
12 me 800 1000 1000
13 me 0 1000 1000
14 me 2000 2000 1000
15 me 1900 2000 2000
Fixed order of resetting I and LAG(I) call.