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Variable number of loops

2 messages · WRAY NICHOLAS, Bert Gunter

Original
WRAY NICHOLAS
# 
I am trying to build a programme which will work out the permutations of a
number of variables, eg a=0 to 1, b=0 to 1, and c=0 to 2, so permutations
would be (0,0,0), (1,0,0), (0,1,0)... etc In this case there would be 2 x
2x 3 = 12 permutations.  If the number of variables are fixed it's easy to
loop round with nesting

However I don't have a fixed number of variables, so I have a variable
number of loops.  I am trying to use a recursive function to do this and
have been building it up step-wise

I want to return a list of all the permutations at the end, but the
programme I have so ar doesn't return a full list, but just the first
element

2 things -- 1 I don't see why this is happening, and 2 is this the right
way to approach this problem?  I cannot find find anything about this in R
on the net

recursfunc1<-function(xf,shiftvecf,vlistf){
  if(xf<4){
    xf<-xf+1
    vlistf[[length(vlistf)+1]]<-shiftvec[xf]
    #print(paste(xf,"and",shiftvec[xf]))
    print(vlistf)
    #print(shiftvec[xf])
    xf<-recursfunc1(xf,shiftvecf,vlistf)}
  return(vlistf)}

shiftvec<-c(2,1,1,0)
vlist<-list()
perm<-recursfunc1(xf=0,shiftvecf=shiftvec,vlistf=vlist)
perm

I want perm to return the elements of shiftvec as a list so that I can then
do all the permutations as the next stage, but it only returns the first
element of shiftvec

Thanks, Nick Wray
Bert Gunter
# 
Are you trying to reinvent ?expand.grid   ?

-- 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, May 15, 2015 at 1:40 PM, WRAY NICHOLAS
<nicholas.wray at ntlworld.com> wrote: