Summing over the column

[Statsconsultancy]

I have a data set like as follows

PatientID  year  adherence

1               1        0

1               2       1

1               3       1

2               1       1

2               2      1

3               1       1

3               2       1

3               3       0

3               4       1  

What i want is to create a new variable that will give cumulative adherence at year "i". Thus the data with a new variable will look like

PatientID  year    adherence  cumulativeAdherence

1              1           0               0

1              2           1               1

1              3           1               2

2              1           1               1

2              2           1               2

3              1           1              1

3              2           1              2

3              3           0              2

3              4           1              3

[art297]

Couldn't you just use something like:

data want;

   set have;

   by PatientID;

   if first.PatientID then cumulativeAdherence=adherence;

   else cumulativeAdherence+adherence;

run;