st: creating count within id clarification

["Richard Hiscock" <rhiscock@netspace.net.au>]

Thanks for you quick reply
Sorry that is was not clear. I have added  visitno[_n] - that is 
obtained from program statement
& visitno to indicate what Im after.
the date can be the same for different ids and the number of 
observations for each date
with id can vary from 1-20+. The final aim is to generate summary data 
(max value, means etc) for var* at each date within id

I have the following data structure

   id       date        var1        var2    visitno   visitno[_n]

   1        16267         x         53        1            1
   1        16267         y        106       1            2
   1        16267         y        84         1            3
   1        16267         y        90         1            4
   1        16267         z         76        1            5
   1        16267         z         65        1            6
   1        16298         x         87        2            1
   1        16298         y        76         2            2
   2        15678         x        98         1            1
   2        15678         y        98         1            2
   2         16541        x        150       2            1
   2        16541        x          76        2            2
   2        16541        x          76        2            3
   2        16541        y           56       2            4

thanks Richard 

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