R help - Jan 2011 - subloop - flexible coding - variable number of loops

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).

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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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)
>
>          }
>
>        }
>
>      }
>
>    }
>
>
> This email may be confidential and subject to legal privilege, it may
> not reflect the views of the University of Canterbury, and it is not
> guaranteed to be virus free. If you are not an intended recipient,
> please notify the sender immediately and erase all copies of the  
> message
> and any attachments.
>
> Please refer to http://www.canterbury.ac.nz/emaildisclaimer for more
> information.
>
> 	[[alternative HTML version deleted]]
>
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David Winsemius, MD
West Hartford, CT