topic Re: Use previous row value of one variable for a new variable in SAS Programming

Use previous row value of one variable for a new variable

eemrun — Mon, 21 Aug 2017 03:04:39 GMT

I have a table where I need a new variable (P_Current) that takes value of the previous value of variable (Current) . The following highlights what I am looking for:

ID	Current	P_Current
1	1	1
2	0	1
2	1	0
3	0	1
4	0	0
5	1	0
6	1	1

I was trying the following but thats probably not correct

data test2;
set test1;
by ID;
P_Current = lag(Current);
if first.ID then P_Current = Current;
run;

Re: Use previous row value of one variable for a new variable

ChrisNZ — Mon, 21 Aug 2017 02:58:39 GMT

Your output seems to macth this code:

data test2;
set test1;
P_Current = lag(Current);
if _N_=1 then P_Current = Current;
run;

Re: Use previous row value of one variable for a new variable

eemrun — Mon, 21 Aug 2017 03:06:44 GMT

Thanks Chris. However, that code does not seem to be working. I have slightly edited the original post table. Ideally I am looking to populate the P_Current field with the last Current value (i.e. value from the previous row). With the code you suggested, the P_Current is populated with all 1s. Any idea where I might be going wrong?

Re: Use previous row value of one variable for a new variable

PGStats — Mon, 21 Aug 2017 04:07:13 GMT

@ChrisNZ's code is working:

data test1;
input ID Current;
datalines;
1 1
2 0
2 1
3 0
4 0
5 1
6 1
;

data test2;
set test1;
P_Current = lag(Current);
if _N_=1 then P_Current = Current;
run;

proc print data=test2 noobs; run;

                            ID    Current    P_Current

                              1       1           1
                              2       0           1
                              2       1           0
                              3       0           1
                              4       0           0
                              5       1           0
                              6       1           1

Please post the code you tried.

Re: Use previous row value of one variable for a new variable

eemrun — Fri, 25 Aug 2017 03:34:47 GMT

my apologies! i got the code wrong. chris's code is indeed correct.