SAS counter reset

[PetePatel]

Spoiler

Hi SAS Community.

I have a dataset with three variables and I am trying to create the fourth one 'need'

'Need' is months since Flag is last>0 resetting to 1 once flag>0. I hope I explained this correctly, but essentially you can see how the variable should be created from the datastep below.

The dataset is already sorted by ID and Date. How can I code this efficiently?

Datastep is below:

data have;
input ID Mon $ Flag Need;
datalines;
1 Jan-06 0 0
1 Feb-06 0 0
1 Mar-06 0 0
1 Apr-06 0 0
1 May-06 0 0
1 Jun-06 0 0
1 Jul-06 0.7 1
1 Aug-06 0 2
1 Sep-06 1 1
1 Oct-06 1.3 1
1 Nov-06 0 2
1 Dec-06 0 3
2 Feb-14 0 0
2 Mar-14 0 0
2 Apr-14 0 0
2 May-14 0 0
2 Jun-14 0.6 1
2 Jul-14 0 2
2 Aug-14 0 3
2 Sep-14 0 4
2 Oct-14 0 5
2 Nov-14 2 1
3 Aug-18 0 0
3 Sep-18 0 0
3 Oct-18 0 0
3 Nov-18 0 0
3 Dec-18 0 0
;
run;

[Kurt_Bremser]

Easily done with a retained variable that is set or incremented on conditions:

data have;
input ID Mon $ Flag Need;
datalines;
1 Jan-06 0 0
1 Feb-06 0 0
1 Mar-06 0 0
1 Apr-06 0 0
1 May-06 0 0
1 Jun-06 0 0
1 Jul-06 0.7 1
1 Aug-06 0 2
1 Sep-06 1 1
1 Oct-06 1.3 1
1 Nov-06 0 2
1 Dec-06 0 3
2 Feb-14 0 0
2 Mar-14 0 0
2 Apr-14 0 0
2 May-14 0 0
2 Jun-14 0.6 1
2 Jul-14 0 2
2 Aug-14 0 3
2 Sep-14 0 4
2 Oct-14 0 5
2 Nov-14 2 1
3 Aug-18 0 0
3 Sep-18 0 0
3 Oct-18 0 0
3 Nov-18 0 0
3 Dec-18 0 0
;

data want;
set have (rename=(need=want_need));
by id;
if first.id then need = 0;
if flag ne 0 then need = 1;
else if need ne 0 then need + 1;
run;

The retain is done automatically because of the use of the SUM Statement (need + 1).