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

[Randall Pruim]

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


> 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
> 
> 	[[alternative HTML version deleted]]
> 
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