[R-sig-teaching] count the number of argument of a function

[Martin Maechler]

>>>>> Randall Pruim <rpruim at calvin.edu>
>>>>>     on Tue, 20 Oct 2015 21:15:14 +0000 writes:

    > A couple more questions for you:
    > * what type of object do you want created?  (A matrix? data frame? something else?)

    > * is there a reason to have 3 named arguments and then … if you are treating them all the same in the end anyway?  Seems like that just makes your function less flexible and harder to code.  But I don’t know your use case.

    > As the previously sent example shows, you can easily apply cbind to all of the items in … (without needing to know how many there were).  I’m now guessing that your attempt to calculate m was not needed.  You can always recover it from the number of columns in the object produced by cbind() if you need it later.

    > Good luck with what I hope is the more interesting part of your programming project that comes after this.

    > —rjp

Sorry to be a bit sarcastic, but if you had not *mis*used
R-SIG-teaching  and rather used  R-help  for asking a somewhat
basic question about R, you would have gotten better answers
more quickly than all the preceding answers: 

The answer is to use  nargs()
[which even in its name suggests  to give what you ask in the
 e-mail subject of this thread]

Martin Maechler

    >> On Oct 20, 2015, at 4:17 PM, Steven Stoline <sstoline at gmail.com> wrote:
    >> 
    >> Dear Michael:
    >> 
    >> Thank you very much for your quick reply.
    >> 
    >> Just one more thing. Assume we have these three data sets (vectors), but
    >> could be 4, 5  or more data sets.
    >> 
    >> x1<-c(1,2,3,4,5)
    >> x2<-c(11,22,33,44,55)
    >> x3<-c(111,222,333,444,555)
    >> 
    >> 
    >> Inside the same fumction I do need to use the cbind() function to cbind
    >> these m (m could be 2, 3, 4, or any numbers) data sets. This what I trired,
    >> but it did not work.
    >> 
    >> f <- function(x1,x2,x3){
    >> m<-length(formals(sys.function()))
    >> 
    >> print(m)
    >> 
    >> data<-cbind(x1,x2,...,xm)                                   #### I need
    >> some help with this part
    >> 
    >> print(data)
    >> 
    >> }
    >> 
    >> f(x1,x2,x3)
    >> 
    >> 
    >> 
    >> with thanks
    >> steve
    >> 
    >> 
    >> 
    >> On Tue, Oct 20, 2015 at 3:51 PM, Michael Weylandt <
    >> michael.weylandt at gmail.com> wrote:
    >> 
    >>> On Tue, Oct 20, 2015 at 2:45 PM, Steven Stoline <sstoline at gmail.com>
    >>> wrote:
    >>> 
    >>>> Dear All:
    >>>> 
    >>>> I am wondering whether there is a way to read and assign the number of
    >>>> arguments of a function inside this function.
    >>>> 
    >>>> 
    >>>> ### For example
    >>>> 
    >>>> fun<-function(x1,x2,x3,...){
    >>>> 
    >>>> m<- number of arguments
    >>>> 
    >>>> }
    >>>> 
    >>>> ### e.g.
    >>>> 
    >>>> fun<-function(x1,x2,x3){
    >>>> 
    >>>> m<- number of arguments
    >>>> 
    >>>> ### m =3 in this case
    >>>> 
    >>>> }
    >>>> 
    >>>> ### e.g.
    >>>> 
    >>>> fun<-function(x1,x2,x3,y1,z1,z2){
    >>>> 
    >>>> m<- number of arguments
    >>>> 
    >>>> ### m =6 in this case
    >>>> 
    >>>> }
    >>>> 
    >>> 
    >>> 
    >>> It's not entirely kosher, but
    >>> 
    >>> length(formals(sys.function()))
    >>> 
    >>> will work.
    >>> 
    >>> f <- function(a, b,c, d, e, f){
    >>> length(formals(sys.function()))
    >>> }
    >>> 
    >>> f() ## 6
    >>> 
    >> 
    >> 
    >> 
    >> -- 
    >> Steven M. Stoline
    >> 1123 Forest Avenue
    >> Portland, ME 04112
    >> sstoline at gmail.com
    >>