On Tue, 15 Sep 2015, Bert Gunter wrote:
Thanks to both Davids.
I realize that these things are often a matter of aesthetics -- and
hence have little rational justification -- but I agree with The Other
David: eval(parse) seems to me to violate R's soul( it makes R a macro
language instead of a functional one).
However, mapply(... switch) effectively loops through the frame row by
row. Aesthetically, I like it; but it seems inefficient. If there are
e.g. 1e6 rows in say 10 categories, I think Jeff's approach should do
much better. I'll try to generate some actual data to see unless
someone else beats me to it.
Use mapply like this on large problems:
unsplit(
mapply(
function(x,z) eval( x, list( y=z )),
expression( A=y*2, B=y+3, C=sqrt(y) ),
split( dat$Flow, dat$ASB ),
SIMPLIFY=FALSE),
dat$ASB)
Chuck
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