[R] Evaluation of variable assigned to a function name

carol white wht_crl at yahoo.com
Mon Jan 10 19:21:21 CET 2011 

I want to make an abstraction of the parameters (assuming that they are unknown) 
for the user-defined function. Is it possible?

In the bar function, if the user doesn't define any function, my.func will be 
invoked with known parameters (if part of the code). If the user defines his own 
function, his function will be invoked in the bar function instead of my.func 
(the else part of the code). The value of either function (my.func or 
my.func.user) will be returned and used in the rest of the bar function.

Is there any thing else that should be clarified?



----- Original Message ----
From: Uwe Ligges <ligges at statistik.tu-dortmund.de>
To: carol white <wht_crl at yahoo.com>
Cc: r-help at stat.math.ethz.ch
Sent: Mon, January 10, 2011 7:14:00 PM
Subject: Re: [R] Evaluation of variable assigned to a function name



On 10.01.2011 18:24, carol white wrote:
> If it doesn't make sense, how to invoke in the bar function, my.func with
> specified parameters with known values and how to invoke my.func.user if the
> user defines his own function (without specifying the parameters)?


he arguments must be specified in arglist, of course.

I guess you want something completely different, hence it might make 
sense to explain what you really intend to do and what your code is so far.

Uwe Ligges



>
>
> ----- Original Message ----
> From: Uwe Ligges<ligges at statistik.tu-dortmund.de>
> To: carol white<wht_crl at yahoo.com>
> Cc: r-help at stat.math.ethz.ch
> Sent: Mon, January 10, 2011 6:10:58 PM
> Subject: Re: [R] Evaluation of variable assigned to a function name
>
>
>
> On 10.01.2011 16:41, carol white wrote:
>> Note that I will call my function or user-defined function in bar function to
>> have the value that my or user-defined function returns. So how can these
>> function be invoked? Can it be like this?
>>
>> bar<- function(arglist, foo){
>>        if(missing(foo)) {
>>              foo<- my.func
>>            v = my.func(x = 2)
>>        }
>>       else{
>>            foo<- my.func.user
>
> The line abopve does nt make sense now, the rest seems to be fine.
>
> Uwe
>
>
>>            v<- do.call(foo, arglist) # since arglist is not known in advance
>>       }
>>        return(v*3)
>> }
>>
>>
>>
>> ----- Original Message ----
>> From: Uwe Ligges<ligges at statistik.tu-dortmund.de>
>> To: carol white<wht_crl at yahoo.com>
>> Cc: r-help at stat.math.ethz.ch
>> Sent: Mon, January 10, 2011 3:04:19 PM
>> Subject: Re: [R] Evaluation of variable assigned to a function name
>>
>>
>>
>> On 10.01.2011 14:56, carol white wrote:
>>> Let the following definitions:
>>>
>>>
>>> # my definition
>>> my.func<- function (x,y,z){
>>> ....
>>> return (v)
>>> }
>>>
>>> # user-defined definition
>>> my.func<- function (x){
>>> ...
>>> return(v)
>>> }
>>>
>>> Considering that my.func can have different parameters but always return a
>>> vector, how to use v in bar by initializing parameters when calling my.func
> (x
>>> =
>>> 2 or a = 3,y=4,z=5)? How can my.func could be invoked in bar and v could be
>>> used?
>>
>>
>> Well, both versions will need the same number of arguments unless you
>> want to pass the as well. Example:
>>
>> bar<- function(arglist, foo){
>>        if(missing(foo)) foo<- my.func
>>        v<- do.call(foo, arglist)
>>        return(v*3)
>> }
>>
>> my.func<- function(x,y,z){
>>        return(x+y+z)
>> }
>>
>> my.func.user<- function(x){
>>       return(x)
>> }
>>
>>
>> Then you can do, e.g.:
>>
>> bar(arglist=list(x=1, y=2, z=3))
>>
>> bar(arglist=list(x=1), foo=my.func.user)
>>
>>
>> Hope this clarifies the idea.
>>
>> Best,
>> Uwe
>>
>>
>>
>>
>>
>>
>>>
>>> bar<- function(x, ....., foo){
>>>>         if(missing(foo)) foo<- Namespace::my.func
>>>>         .....
>>>> }
>>>
>>>
>>>
>>> ----- Original Message ----
>>> From: Uwe Ligges<ligges at statistik.tu-dortmund.de>
>>> To: carol white<wht_crl at yahoo.com>
>>> Cc: r-help at stat.math.ethz.ch
>>> Sent: Mon, January 10, 2011 2:48:04 PM
>>> Subject: Re: [R] Evaluation of variable assigned to a function name
>>>
>>>
>>>
>>> On 10.01.2011 14:39, carol white wrote:
>>>> In fact, what the function is returning is the most important. So knowing
>> that
>>>> the parameters and the number of parameters of my.func defined by the user
>>>> could
>>>> be different from one definition to another, how to use what my.func 
returns
>>> in
>>>> other functions? Moreover, if the function is defined by the user in an R
>>>> session, it is then defined globally. In this case, does it need to be
> passed
>>>> as
>>>> a parameter? Note that my.func defined by me is loaded before.
>>>
>>> It depends.
>>>
>>> 1. The output of a function can always be wrapped in a list.
>>> 2. You should always pass objects that you want to use in another
>>> environment unless you really know what you are doing - and reading does
>>> not suggest you are too sure about it.
>>> 3. In this case, if your package has a Namespace, your own function
>>> rather than a user generated one in the .GlobalEnv will be found.
>>>
>>> Note that defining stuff in .GlobalEnv and relying on the fact that this
>>> version is found by another function would imply you really have to get
>>> it from the specific environment.
>>>
>>> Best,
>>> Uwe
>>>
>>>
>>>
>>>
>>>> Carol
>>>>
>>>>
>>>>
>>>> ----- Original Message ----
>>>> From: Uwe Ligges<ligges at statistik.tu-dortmund.de>
>>>> To: carol white<wht_crl at yahoo.com>
>>>> Cc: r-help at stat.math.ethz.ch
>>>> Sent: Mon, January 10, 2011 2:11:48 PM
>>>> Subject: Re: [R] Evaluation of variable assigned to a function name
>>>>
>>>> Wel, just let the user give the function in form of an argument, say
>>>> "foo", and use your code so that
>>>>
>>>>
>>>> bar<- function(x, ....., foo){
>>>>         if(missing(foo)) foo<- Namespace::my.func
>>>>         .....
>>>> }
>>>>
>>>>
>>>> but perhaps I misunderstood your question.
>>>>
>>>> Uwe Ligges
>>>>
>>>>
>>>>
>>>> On 10.01.2011 13:47, carol white wrote:
>>>>> Hi,
>>>>> I have defined a function (my.func) which is used as parameter (f) of
>> another
>>>>> function. As I want to give the user the possibility to define his own
>>>> function
>>>>> instead of my.func, how can I find out if in other functions, the 
parameter
>> f
>>>>> has the my.func value (if the user has defined a new function or not)?
>>>>>
>>>>>
>>>>> Moreover, I think I should impose to the user to use another function name
>>>> than
>>>>> my.func for this (?). Or a boolean variable is better to be used to
> indicate
>>>> if
>>>>> my function (my.func) or user-defined function is used?
>>>>>
>>>>> Thanks
>>>>>
>>>>> Carol
>>>>>
>>>>> ______________________________________________
>>>>> R-help at r-project.org mailing list
>>>>> 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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