Hi everyone, I have a data sample like this:   Firm  Year        IPO_year  A       2000       0 A       2001       1 A       2002       0 A       2003       0 B       2007       0 B       2008       1 B       2009       0 C       2013       0 C       2014       0   I want to count the number of years after IPO for each firm, so what I want to get is another column like this: Firm  Year        IPO_year       Year_After_IPO A       2000       0                     0 A       2001       1                     1 A       2002       0                     2 A       2003       0                     3 B       2007       0                     0 B       2008       1                     1 B       2009       0                     2 C       2013       0                     0 C       2014       0                     0 (All the years before IPO will be zero).   I have tried this code:  data X;     set Y; by Firm; if IPO_year = 1 then d+1;     run;   but this code is not reset for new firm. Could any one can help me with this? Thank you very much in advance! ... View more