[R] subloop - flexible coding - variable number of loops

[David Winsemius]

On Jan 27, 2011, at 6:29 PM, Peter Jaksons wrote:

> Hello,
>
>
>
> I want to create a flexible code for the following example: In stead  
> of
> using a different code for each n (as in my example below), I want to
> write a general code for every n (n from 1 to 10).

Have you done any thinking about the size of hte programming task?  
Perhaps running this code?

 > 20^(1:10)
  [1] 2.000e+01 4.000e+02 8.000e+03 1.600e+05 3.200e+06 6.400e+07  
1.280e+09 2.560e+10 5.120e+11 1.024e+13

So you might want to think twice about trying for n > 6 right off the  
bat/

expand.grid could be used:

col3 <- expand.grid(as.data.frame(matrix(rep(1:20, 3), ncol=3)))
col3[apply(col3, 1,sum)==20, ]

 > nrow( col3[apply(col3, 1,sum)==20, ] )
[1] 171

-- 
David.


>
> I tried a lot of things, but I always got stuck with the number of
> subloops or witch closing the brackets. Any suggestions?
>
>
>
> Cheers,
>
>
>
> Peter
>
>
>
> Department of Mathematics and Statistics
>
> University of Canterbury
>
> New Zealand
>
>
>
>
>
> n <-2
>
>
>
> matrixallo <- matrix(nrow=0,ncol=n)
>
>
>
> for(i in 1:20)
>
>    {
>
>    for (j in 1:20)
>
>      {
>
>      if (i+j == 20)
>
>        {
>
>        newentry<- cbind(i,j)
>
>        matrixallo <- rbind(matrixallo,newentry)
>
>        }
>
>      }
>
>    }
>
>
>
>
>
> n <-3
>
>
>
> matrixallo <- matrix(nrow=0,ncol=n)
>
>
>
>  for(i in 1:20)
>
>    {
>
>    for (j in 1:20)
>
>      {
>
>      for (k in 1:20)
>
>        {
>
>        if (i+k+j == 20)
>
>          {
>
>          newentry<- cbind(i,j,k)
>
>          matrixallo <- rbind(matrixallo,newentry)
>
>          }
>
>        }
>
>      }
>
>    }
>
>
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David Winsemius, MD
West Hartford, CT