[R] SAS to R migration questions

[Fernando Henrique Ferraz P. da Rosa]

Matthew Wilson writes:
> (...)
> Step 3:
> 
> I print a list of number of sales per customer ID, ranking the customer
> IDs from most to least.  I use a SAS proc freq step for this:
> 
>     proc freq data=d2 order=freq;
>         tables custid;
>     run;
> 
> and the output would look like this:
> 
>     custid      freq
>     111         2
>     112         1
> 
> 
> Again, I have no idea how to do step 3 in R.  

        Provided that you are going to work with this data stored in a
SQL database, it'll probably be more efficient to do this sort of
manipulation directly in SQL. Anyways, the following lines of code in R
will do what you described:

cust <- c(111,111,112)
cc <- data.frame(t(sapply(unique(cust),function(level,vec) {
c(custid=level,freq=sum(vec==level)) },cust))) 
cc[order(cc$freq,decreasing=T),]


Cheers,

--
Fernando Henrique Ferraz P. da Rosa
http://www.ime.usp.br/~feferraz