[R] Problem with apply list to function: numerical expression has 4 elements: only the first used

[David Winsemius]

> On May 24, 2015, at 6:35 AM, Narua <maria.mi8 at gmx.de> wrote:
> 
> Dear kd,
> thanks for your fast reply 
> hm, I thougth, F is normally the abbrevation, but in R FALSE represents
> "false"?
> Anyway, your function works and I got the idea to work with "apply" 
> 
> I had actually a little more complicate functions (put I posted in the forum
> first an easier example):
> f<-function(a,b)((1/(sum(sqrt(1:a))))*sqrt(b))
> F<-function(a,b)(sum(f(a,1:b)))
>> F(5,3)
> [1] 0.4946433
>> F(5,5)
> [1] 1
> therefore, 0.4946433 is the distribution of b=3 with a=5 Elements.
> 
> FInv<-function(s,a,b) if(isTRUE(all.equal(F(a,b),s, tolerance=0.00001)))
> cat("F(",s,",",a,",",b,") equals s; ") else cat("F(",a,",",b,") does not
> equal to s; ")
> FInv is the reverse function. you put a probability in the function and
> recieve the distribution b of a special a.
> I wanted to have a function FInv' to pass on s for all a and all b to
> FInv(s,a,b) in order to find out, which probability fits to which a and b.
> 
> And I couln't pass on a and b so easily, I got the error: "In 1:i :
> numerical expression has 4 elements: only the first used "
> I think, the reason is, that R expects a number, but receives a list, and
> that produces the error.

No. First off, it’s not an error but rather a warning. Here’s the easiest way of seeng what produces it>

> m=1:4
> 1:m
[1] 1
Warning message:
In 1:m : numerical expression has 4 elements: only the first used

— David.
> 

> 
> I tried 
>> x<-c(1:10)
>> FooInv<-function(s) foreach(i=1:10)%do%sapply(x,FInv,s=s,k=i) and that
>> works:
>> FooInv(0.4946433)
> F(s = 0.4946433 ,m = 5 ,k = 3 ) equals s; [[1]]
> 
> Foreach is a for-loop, and sapply matches FInv for every element of the list
> x.
> 
> But now another problem occured:
> Obviously R gets anywhere a NULL-pointer, because the full output is:
> F(s = 0.4946433 ,m = 5 ,k = 3 ) equals s; [[1]]
> [[1]][[1]]
> NULL
> 
> [[1]][[2]]
> NULL
> 
> [[1]][[3]]
> NULL
> 
> [[1]][[4]]
> NULL
> 
> [[1]][[5]]
> NULL
> ...
> in every loop.
> 
> Do you or someone else know how  I can get rid of the NULL-outputs?
> 
> if this problem is solved, I have all I need in order to calculate the
> distribution and its inverse function :-)
> 
> Thanks in advance,
> Narua 
> 
> 
> 
> --
> View this message in context: http://r.789695.n4.nabble.com/Problem-with-apply-list-to-function-numerical-expression-has-4-elements-only-the-first-used-tp4707588p4707612.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> 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.

David Winsemius, MD
Alameda, CA, USA