On Sep 15, 2015, at 7:20 PM, Charles C. Berry wrote:
> 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$ASB)
>
Seems unnecessarily complex, but definitely elegant. Was there a reason it was
not just:
mapply(
function(x,z) eval( x, list( y=z )),
expression(A= y*2, B=y+3, C=sqrt(y) ),
split( dat$Flow, dat$ASB )
)
Also readers should note that the names in that expression vector are quite
arbitrary at the moment. The only association is via the order. I don't suppose
someone wants to take on the challenge of matching the names of the expression
vector with the names of returned split components?
> Chuck
David Winsemius
Alameda, CA, USA
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