update data in data step

[duanzongran]

DEAR ALL:

HERE ,I have a dataset:

data lin;
input x;
datalines;
1
2
3
4
.
.
.
;
run;

the  missing value should be updated  like this 

the 5th obs=(1+2+3+4)=10

the 6th obs=1+2+3+4+The5thObs=(1+2+3+4+10)=20;

the 7th obs=1+2+3+4+The5thObs+The6thObs=(1+2+3+4+10+20)=40;

........

the expected result is a sequence like a sequence

1

2
3
4
10
20
40

[PeterClemmensen · Accepted solution]

data want(keep=x);
    set lin;
    s+x;
    if x=. then do;
        x=s;
        s+x;
    end;
run;

Result:

x
1
2
3
4
10
20
40

[Kurt_Bremser]

Use a retained variable:

data lin;
input x;
datalines;
1
2
3
4
.
.
.
;

data want;
set lin;
retain _x 0;
if x = . then x = _x;
_x + x;
drop _x;
run;