Matrix: Problem with the code

On Fri, Jan 9, 2009 at 6:36 PM,  <markleeds at verizon.net> wrote:

Charlotte: I ran your code because I wasn't clear on it and your way 
would
cause more matrices than the person requested.

Bhargab gave us

     x<-c(23,67,2,87,9,63,8,2,35,6,91,41,22,3)

and said: "I want to have a matrix with p columns such that each
column will have the elements of  x^(column#)."

so, I think Charlotte's code was spot-on:

p <- 3
outer(x, 1:p, '^')
     [,1] [,2]   [,3]
 [1,]   23  529  12167
 [2,]   67 4489 300763
 [3,]    2    4      8
 [4,]   87 7569 658503
 [5,]    9   81    729
 [6,]   63 3969 250047
 [7,]    8   64    512
 [8,]    2    4      8
 [9,]   35 1225  42875
[10,]    6   36    216
[11,]   91 8281 753571
[12,]   41 1681  68921
[13,]   22  484  10648
[14,]    3    9     27


Here's another way -- a bit less elegant, but a gentle
introduction to thinking in vectors rather than elements:

 mat <- matrix(0,nrow=length(x), ncol=p)

 for(i in 1:p) mat[,i] <- x^i
 mat
     [,1] [,2]   [,3]
 [1,]   23  529  12167
 [2,]   67 4489 300763
 [3,]    2    4      8
 [4,]   87 7569 658503
 [5,]    9   81    729
 [6,]   63 3969 250047
 [7,]    8   64    512
 [8,]    2    4      8
 [9,]   35 1225  42875
[10,]    6   36    216
[11,]   91 8281 753571
[12,]   41 1681  68921
[13,]   22  484  10648
[14,]    3    9     27


best,

Kingsford Jones






So

I think the code below it, although not too short, does what the 
person
asked. Thanks though because I understand outer better now.

temp <- matrix(c(1,2,3,4,5,6),ncol=2)
print(temp)

#One of those more elegant ways:
print(temp)
outer(temp,1:p,'^')One of those more elegant ways:


# THIS WAY I THINK GIVES WHAT THEY WANT

sapply(1:ncol(temp), function(.col) {
 temp[,.col]^.col
})



On Fri, Jan 9, 2009 at  7:40 PM, Charlotte Wickham wrote:

One of those more elegant ways:
outer(x, 1:p, "^")

Charlotte

On Fri, Jan 9, 2009 at 4:24 PM, Sarah Goslee 
<sarah.goslee at gmail.com>
wrote:

Well, mat doesn't have any dimensions / isn't a matrix, and we 
don't
know what p is supposed to be. But leaving aside those little 
details,
do you perhaps want something like this:

    x<-c(23,67,2,87,9,63,8,2,35,6,91,41,22,3)
    p <- 5
    mat<- matrix(0, nrow=p, ncol=length(x))
    for(j in 1:length(x))
    {
        for(i in 1:p)
            mat[i,j]<-x[j]^i
    }

Two notes: I didn't try it out, and if that's what you want rather
than a toy example
of a larger problem, there are more elegant ways to do it in R.

Sarah

On Fri, Jan 9, 2009 at 6:42 PM, Bhargab Chattopadhyay
<bhargab_1 at yahoo.com> wrote:

Hi,


Can any one please explain why the following code doesn't work? Or 
can
anyone suggest an alternative.
Suppose
     x<-c(23,67,2,87,9,63,8,2,35,6,91,41,22,3)
      mat<-0;
      for(j in 1:length(x))
      {
         for(i in 1:p)
              mat[i,j]<-x[j]^i;
      }
  Actually I want to have a matrix with p columns such that each 
column
will have the elements of  x^(column#).

Thanks in advance.

Bhargab

--
Sarah Goslee
http://www.functionaldiversity.org