st: using creat count id on var

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

Thanks Nick for your reply
Im obviously finding it difficult to develop in this area
I cant find a useful guide,any pointers?

My problem now is that having identified the visitno within id I wish to 
perform manipulations on a variable. For example
using the illustrated structure.
To obtain the maximum value of var1 within id at each level  of visitno.
To obtain the mean value of var1 within id at each level of visitno

   id           date          visitno      var1

>     1        16267         1             53
>     1        16267         1            106
>     1        16267         1            84
>     1        16267         1            90
>     1        16267         1            76
>     1        16267         1            65
>     1        16298         2             87
>     1        16298         2            76
>     2        15678         1            98
>     2        15678         1            98
>     2         16541        2            150



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