On 27/09/2012 12:13 PM, Pradipto Banerjee wrote:
I am evaluating a switch from Stata to R. I don't need to extensive Statistical
methods, but the main reason I am exploring the switch is the coding
flexibility in R (e.g. Stata does not support linear/quadratic programming). I
have been going over the R syntax and I had a quick question:
In Stata, one has a very useful construction called "by", e.g.
by month signal: gen xxx = myfunction(yyy zzz) if cond1==cond2
Similarly, in SAS, one can write
by monthn signal;
if cond1=cond2 then xxx = myfunction(yyy zzz);
run;
I looked at a lot of R tutorials, but I haven't come across the equivalent of the Stata
or SAS "by" construct in R?
There's a by() function, and also the more general tapply(). There are
also contributed packages with related functions, e.g. the sparseby()
function in the reshape package. I believe the reshape2 package has the
same functionality, but I forget what function does it.
Duncan Murdoch
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