[R] Apply a multi-variable function to a vector
Jeff Newmiller
jdnewmil at dcn.davis.ca.us
Sat Sep 10 07:29:22 CEST 2016
Not sure I understand what you really want, if you have found ways to
accomplish what you want but are not satisfied with them. That is one
reason why keeping the mailing list involved (by reply-all) is good for
you. From my end, I don't do one-on-one support online, and may not be
able to carry on a thread to the end if I get busy.
Your concept of a generalized outer function sounds to me like:
myfunc <- function( A, B, C ) {
A * B + C
}
gouter <- function( FUN, ... ) {
args <- list( ... )
DF <- do.call( expand.grid, args )
array( data = do.call( FUN, DF )
, dim = sapply( args, FUN=length )
, dimnames = args
)
}
gouter( myfunc, A = 1:3, B=2:6, C=3:4 )
# , , C = 3
#
# B
# A 2 3 4 5 6
# 1 5 6 7 8 9
# 2 7 9 11 13 15
# 3 9 12 15 18 21
#
# , , C = 4
#
# B
# A 2 3 4 5 6
# 1 6 7 8 9 10
# 2 8 10 12 14 16
# 3 10 13 16 19 22
I generally just tack on columns to the expand.grid result... I almost
never have a need for multidimensional arrays.
On Fri, 9 Sep 2016, Steve Kennedy wrote:
> Hello,
>
> Abstraction is what I want. I'm actually looking to do something more
> complicated. The functions do.call, and as.list get me most of the way
> there, but there is something I'm missing ...
>
> My eventual goal is to produce a multi-dimensional version of 'outer'.
> Like my.outer(func, a_vec, b_vec, c_vec, ..), where the function of the
> variables 'a', 'b', 'c', etc. would be applied to the vectors from the
> outer product of the vectors of values for each variable.
>
> I wanted to use expand.grid (does require reshaping the output). Using
> temps = c(40,50,60) and times = c(1:5), this doesn't quite seem to work:
>
> apply(expand.grid(temps,times), 1, function(a) do.call(func2, as.list(a)))
>
> although this does work:
>
> do.call(func2, as.list(c(10, 121)))
>
> And, this also works:
>
> apply(expand.grid(temps,times), 1, function(a) do.call("+", as.list(a)))
>
> There is some subtlety here I don't understand.
>
> Thanks,
>
> Steve
>
> -----Original Message-----
> From: Jeff Newmiller [mailto:jdnewmil at dcn.davis.ca.us]
> Sent: Friday, September 09, 2016 5:39 PM
> To: Steve Kennedy; r-help at r-project.org
> Subject: Re: [R] Apply a multi-variable function to a vector
>
> Your architecture has a bad smell to me. For one thing you are mixing
> different units in the same vector but should be putting multiple
> instances of the same variable into one vector. Lists of vectors (data
> frames) are typically used when multiple variables need to be grouped.
>
> Another problem is that you are constraining the names of the variables
> you pass to the function to be named the same as they are inside the
> function. This really limits your use of those functions.
>
> There really is too much abstraction going on here.
> --
> Sent from my phone. Please excuse my brevity.
>
> On September 9, 2016 12:44:52 PM PDT, Steve Kennedy <SKennedy at AnikaTherapeutics.com> wrote:
>> Hello,
>>
>> I would like to define an arbitrary function of an arbitrary number of
>> variables, for example, for 2 variables:
>>
>> func2 <- function(time, temp) time + temp
>>
>> I'd like to keep variable names that have a meaning in the problem
>> (time and temperature above).
>>
>> If I have a vector of values for these variables, for example in the
>> 2-d case, c(10, 121), I'd like to apply my function (in this case
>> func2) and obtain the result. Conceptually, something like,
>>
>> func2(c(10,121))
>>
>> becomes
>>
>> func2(10,121)
>>
>> Is there a simple way to accomplish this, for an arbitrary number of
>> variables? I'd like something that would simply work from the
>> definition of the function. If that is possible.
>>
>> Thanks,
>>
>> Steve Kennedy
>>
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