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?




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