[R] Non repetitive permutations/combinations of elements

[Marc Schwartz (via MN)]

Bert,

That will result in a data frame, rather than a matrix:

> str(expand.grid(rep(list(c(-1, 1)), 4)))
`data.frame':   16 obs. of  4 variables:
 $ Var1: num  -1 1 -1 1 -1 1 -1 1 -1 1 ...
 $ Var2: num  -1 -1 1 1 -1 -1 1 1 -1 -1 ...
 $ Var3: num  -1 -1 -1 -1 1 1 1 1 -1 -1 ...
 $ Var4: num  -1 -1 -1 -1 -1 -1 -1 -1 1 1 ...
 - attr(*, "out.attrs")=List of 2
  ..$ dim     : int  2 2 2 2
  ..$ dimnames:List of 4
  .. ..$ Var1: chr  "Var1=-1" "Var1= 1"
  .. ..$ Var2: chr  "Var2=-1" "Var2= 1"
  .. ..$ Var3: chr  "Var3=-1" "Var3= 1"
  .. ..$ Var4: chr  "Var4=-1" "Var4= 1"
 - attr(*, "colnames")= chr  "Var1" "Var2" "Var3" "Var4"


Nameeta asked for a matrix, hence the coercion in my reply.

Best regards,

Marc


On Mon, 2006-05-08 at 14:59 -0700, Berton Gunter wrote:
>  expand.grid(rep(list(c(-1, 1)), 4))  suffices I believe.
> 
> -- Bert Gunter
> Genentech Non-Clinical Statistics
> South San Francisco, CA
>   
> 
> > -----Original Message-----
> > From: r-help-bounces at stat.math.ethz.ch 
> > [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Marc 
> > Schwartz (via MN)
> > Sent: Monday, May 08, 2006 2:50 PM
> > To: Nameeta Lobo
> > Cc: r-help at stat.math.ethz.ch
> > Subject: Re: [R] Non repetitive permutations/combinations of elements
> > 
> > On Mon, 2006-05-08 at 16:32 -0500, Nameeta Lobo wrote:
> > > Hello all,
> > > 
> > > I am trying to create a matrix of 1s and -1s without any 
> > repetitions for a
> > > specified number of columns.
> > > e.g. 1s and -1s for 3 columns can be done uniquely in 2^3 ways.
> > > -1 -1 -1
> > > -1 -1  1
> > > -1  1 -1
> > > -1  1  1
> > >  1 -1 -1
> > >  1 -1  1
> > >  1  1 -1
> > >  1  1  1
> > > and for 4 columns in 2^4 ways and so on.
> > > 
> > > I finally used the function combn([0 1],3) that I found at 
> > the following link
> > > 
> > http://www.mathworks.com/matlabcentral/fileexchange/loadFile.d
> > o?objectId=7147&objectType=FILE
> > > written by Jos van der Geest in Matlab which generated the above.
> > > 
> > > 
> > > How can I do this is R? I have looked at permn and combn in 
> > the combinat library
> > > and permutations and combinations in the gtools library and 
> > I am still confused
> > > as to how to get it to work.
> > > 
> > > Any suggestions will be truly appreciated.
> > > 
> > > Thank you
> > > 
> > > Nameeta
> > > 
> > 
> > With just two elements in the source vector, it may be easiest to just
> > use expand.grid() and coerce the result to a matrix:
> > 
> > > as.matrix(expand.grid(rep(list(c(-1, 1)), 3)))
> >   Var1 Var2 Var3
> > 1   -1   -1   -1
> > 2    1   -1   -1
> > 3   -1    1   -1
> > 4    1    1   -1
> > 5   -1   -1    1
> > 6    1   -1    1
> > 7   -1    1    1
> > 8    1    1    1
> > 
> > Just adjust the final value of '3' to the number of columns that you
> > wish to have:
> > 
> > > as.matrix(expand.grid(rep(list(c(-1, 1)), 4)))
> >    Var1 Var2 Var3 Var4
> > 1    -1   -1   -1   -1
> > 2     1   -1   -1   -1
> > 3    -1    1   -1   -1
> > 4     1    1   -1   -1
> > 5    -1   -1    1   -1
> > 6     1   -1    1   -1
> > 7    -1    1    1   -1
> > 8     1    1    1   -1
> > 9    -1   -1   -1    1
> > 10    1   -1   -1    1
> > 11   -1    1   -1    1
> > 12    1    1   -1    1
> > 13   -1   -1    1    1
> > 14    1   -1    1    1
> > 15   -1    1    1    1
> > 16    1    1    1    1
> > 
> > 
> > HTH,
> > 
> > Marc Schwartz
> >