[R] Multiple if function

[Anthoni, Peter (IMK)]

Hi,

I guess this might work too and might be quite speedy:

ASBclass = factor(c(1,2,2,3,2,1))
Flow = c(1,1,1,1,1,1)

mult = ((ASBclass==1) * 0.1 + (ASBclass==2) * 0.15 + (ASBclass==3) * 0.2)
deviation = mult * Flow

or with the more complex arithmetic:

deviation = ((ASBclass==1) * (Flow*2) + (ASBclass==2) * (Flow+3) + (ASBclass==3) * sqrt(Flow))

cheers
Peter



> On 16 Sep 2015, at 04:20, Charles C. Berry <ccberry at ucsd.edu> 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)
> 
> Chuck
> 
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