[Rd] "by" speed improvement (PR#11064)

[simon.debernard at altrabio.com]

Full_Name: Simon de Bernard
Version: 2.7.0 (44733)
OS: MacOS
Submission from: (NULL) (140.77.34.213)


"by" usually takes forever even on a "not so large" data structure.

If one can do with a matrix instead of a data.frame, defining by.matrix as
by.data.frame modified to convert data back to a data.frame in the "eval" call
improves speed by orders of magnitude (whatever that means ;-) )

I'd suggest defining the by.matrix function directly in R...