[R] Convert numerical value into function which returns numerical value
David Barron
dnbarron at gmail.com
Fri Apr 10 17:49:56 CEST 2015
I'd have a look at Hadley Wickham's online Advanced R here:
http://adv-r.had.co.nz/. It has a section on Functional progamming
that deals with this kind of thing.
David
On 10 April 2015 at 15:28, Bert Gunter <gunter.berton at gene.com> wrote:
> "Is there a good resource for these advanced programming techniques in R?"
>
> 1. I would not consider this "advanced." I would consider "computing
> on the language" techniques and manipulation of environments to be
> advanced, for example.
>
> 2. But anyway, there are tons of R Programming resources. John
> Chambers's books and even the venerable "S Programming" book of
> Venables and Ripley might be worth checking; Hadley Wickham has
> written quite a few web resources that are being developed into a book
> (or have already been) -- you can probably find these by following
> links from the R STudio website or checking his repositories at
> Github. But there are many more both on the Web and in print, and you
> would do better to search on your own to find something that suits
> your learning style and needs rather than relying on my fairly
> uninformed opinion (as I do not teach R and therefore have made no
> effort to be current with the resources).
>
> Cheers,
> Bert
>
> Bert Gunter
> Genentech Nonclinical Biostatistics
> (650) 467-7374
>
> "Data is not information. Information is not knowledge. And knowledge
> is certainly not wisdom."
> Clifford Stoll
>
>
>
>
> On Fri, Apr 10, 2015 at 1:27 AM, Rainer M Krug <Rainer at krugs.de> wrote:
>> Bert Gunter <gunter.berton at gene.com> writes:
>>
>>> 1. An important point that Bill uses but did not explicitly state is
>>> that R is (essentially) a functional programming language, which means
>>> among other things that functions can return functions as values.
>>
>> Yup - that is essential here. A function is also only an object in R,
>> like characters or numeric values.
>>
>>>
>>> 2. As a perhaps slightly amusing variant of Bill's construct that
>>> illustrates this is the function below whose value is a function that
>>> either returns a constant determined when it is defined or its
>>> argument when called if no constant was given to it on definition:
>>>
>>> fconv <- function(arg=NULL){
>>> function(z)if(is.null(arg))z else arg
>>> }
>>
>> You know, this is exactly what I want to do: I have a function, which
>> takes either a numerical value or a function (from PAI) as the argument
>> dep. So I have to check if the dep is a function or a value. At the
>> moment, I am using is.function(), and when dep is not a function,
>> convert it to a function which returns dep. If it is a function, I can
>> leave it as it is. I could also replace, in your code, the is.null()
>> with is.function() and do effectively the same here (some edits
>> required).
>>
>> Very neat indeed.
>>
>> And a perfect way of making functions very versatile. IU really have to
>> look closer into these things.
>>
>> Is there a good resource for these advanced programming techniques in R?
>>
>> Thanks,
>>
>> Rainer
>>
>>
>>>> x <- 5
>>>> g1 <- fconv(x) ## g1 will always return 5
>>>> g1()
>>> [1] 5
>>>> g1(1)
>>> [1] 5
>>>
>>>> x <- 2
>>>> g1(x) ## Still uses the "x" in its defining environment
>>> [1] 5
>>>
>>> ## But ...
>>>> g2 <- fconv() ## No constant given to it in its definition
>>>> g2(x)
>>> [1] 2
>>>> g2(1)
>>> [1] 1
>>>> g2()
>>> Error in g2() : argument "z" is missing, with no default
>>>
>>> Cheers,
>>> Bert
>>>
>>> Bert Gunter
>>> Genentech Nonclinical Biostatistics
>>> (650) 467-7374
>>>
>>> "Data is not information. Information is not knowledge. And knowledge
>>> is certainly not wisdom."
>>> Clifford Stoll
>>>
>>>
>>>
>>>
>>> On Thu, Apr 9, 2015 at 7:57 AM, William Dunlap <wdunlap at tibco.com> wrote:
>>>> You can make such functions by using the fact that a function
>>>> (really, a 'closure') always has access to the environment in
>>>> which the function was created. E.g.
>>>> makeConstantFunction <- function(constant) {
>>>> force(constant) # evaluate the argument now
>>>> function(PAI) {
>>>> constant
>>>> }
>>>> }
>>>> f17 <- makeConstantFunction(17)
>>>> flog17 <- makeConstantFunction(log(17))
>>>> f17(111)
>>>> # [1] 17
>>>> flog17(111)
>>>> # [1] 2.833213
>>>>
>>>> If you print f17 and flog17 they will look the same, except for
>>>> their environments and you have to inspect those to see why
>>>> they act differently.
>>>>
>>>> ls.str(environment(f17))
>>>> # constant : num 17
>>>> ls.str(environment(flog17))
>>>> # constant : num 2.83
>>>>
>>>> If you really want the functions to look different you can use
>>>> substittute or bquote, but that is also a bit mysterious (you need the
>>>> eval()
>>>> their outputs):
>>>> g17 <- eval(substitute(function(PAI)x, list(x=17)))
>>>> h17 <- eval(bquote(function(PAI).(x), list(x=17)))
>>>> g17(10)
>>>> [1] 17
>>>> h17(10:1)
>>>> [1] 17
>>>>
>>>>
>>>>
>>>>
>>>> Bill Dunlap
>>>> TIBCO Software
>>>> wdunlap tibco.com
>>>>
>>>> On Thu, Apr 9, 2015 at 5:39 AM, Rainer M Krug <Rainer at krugs.de> wrote:
>>>>
>>>>>
>>>>> Hi
>>>>>
>>>>> I want convert, in a function, an argument from a numerical value to a
>>>>> function which returns this value.:
>>>>>
>>>>> My Code:
>>>>>
>>>>> --8<---------------cut here---------------start------------->8---
>>>>> dep <- 13
>>>>> dep <- function() {dep}
>>>>> dep
>>>>> --8<---------------cut here---------------end--------------->8---
>>>>>
>>>>> This is what I get:
>>>>> #+RESULTS:
>>>>> ,----
>>>>> | function(PAI) { dep }
>>>>> `----
>>>>>
>>>>> This is what I want
>>>>> ,----
>>>>> | function(PAI) { 13 }
>>>>> `----
>>>>>
>>>>> I thought about using eval(dep), but this gives me the effectively the
>>>>> same.
>>>>>
>>>>> Is it possible to achieve what I want? I somehow have the feeling this
>>>>> is not that easily possible, as the code in the function definition is
>>>>> only evaluated when the function is evaluated.
>>>>>
>>>>> I could obviously do something like
>>>>>
>>>>> --8<---------------cut here---------------start------------->8---
>>>>> dep <- 13
>>>>> depVal <- dep
>>>>> dep <- function() {depVal}
>>>>> dep()
>>>>> --8<---------------cut here---------------end--------------->8---
>>>>>
>>>>> But is there a better solution?
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Rainer
>>>>>
>>>>> --
>>>>> Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
>>>>> Biology, UCT), Dipl. Phys. (Germany)
>>>>>
>>>>> Centre of Excellence for Invasion Biology
>>>>> Stellenbosch University
>>>>> South Africa
>>>>>
>>>>> Tel : +33 - (0)9 53 10 27 44
>>>>> Cell: +33 - (0)6 85 62 59 98
>>>>> Fax : +33 - (0)9 58 10 27 44
>>>>>
>>>>> Fax (D): +49 - (0)3 21 21 25 22 44
>>>>>
>>>>> email: Rainer at krugs.de
>>>>>
>>>>> Skype: RMkrug
>>>>>
>>>>> PGP: 0x0F52F982
>>>>>
>>>>> ______________________________________________
>>>>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>>> PLEASE do read the posting guide
>>>>> http://www.R-project.org/posting-guide.html
>>>>> and provide commented, minimal, self-contained, reproducible code.
>>>>>
>>>>
>>>> [[alternative HTML version deleted]]
>>>>
>>>> ______________________________________________
>>>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>
>> --
>> Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology, UCT), Dipl. Phys. (Germany)
>>
>> Centre of Excellence for Invasion Biology
>> Stellenbosch University
>> South Africa
>>
>> Tel : +33 - (0)9 53 10 27 44
>> Cell: +33 - (0)6 85 62 59 98
>> Fax : +33 - (0)9 58 10 27 44
>>
>> Fax (D): +49 - (0)3 21 21 25 22 44
>>
>> email: Rainer at krugs.de
>>
>> Skype: RMkrug
>>
>> PGP: 0x0F52F982
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
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