[R] Non-procedural access to columns of a matrix

[William Dunlap]

Does the following do what you want?

  > i <- cbind(seq_len(nrow(x)), x[,4])
  > x[i]
  [1] 11 23 32
  > x[i] <- x[i] + 5
  > x
       [,1] [,2] [,3] [,4]
  [1,]   16   12   13    1
  [2,]   21   22   28    3
  [3,]   31   37   33    2

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Joris Meys
> Sent: Friday, June 18, 2010 5:08 PM
> To: Iuri Gavronski
> Cc: r-help
> Subject: Re: [R] Non-procedural access to columns of a matrix
> 
> > diag(x[,x[,4]])
> [1] 11 23 32
> 
> > diag(x[,x[,4]]) <- diag(x[,x[,4]])+5
> > x
>      [,1] [,2] [,3] [,4]
> [1,]   16   12   13    1
> [2,]   21   22   28    3
> [3,]   31   37   33    2
> 
> Cheers
> Joris
> 
> On Fri, Jun 18, 2010 at 8:58 PM, Iuri Gavronski <iuri at ufrgs.br> wrote:
> > Hi,
> >
> > I would like to have an index for a column in a matrix encoded in a
> > cell of the same matrix.
> > For example:
> > x = matrix(c(11,12,13,1,
> > 21,22,23,3,
> > 31,32,33,2),byrow=T,ncol=4)
> >
> > In this case, column 4 is the index. I then access the column
> > specified in the index by:
> >> for (i in 1:3) print(x[i,x[i,4]])
> > [1] 11
> > [1] 23
> > [1] 32
> >>
> >> for (i in 1:3) {x[i,x[i,4]] <- x[i,x[i,4]] + 5}
> >> x
> >     [,1] [,2] [,3] [,4]
> > [1,]   16   12   13    1
> > [2,]   21   22   28    3
> > [3,]   31   37   33    2
> >>
> >
> > Is there a way to get the same results without looping?
> >
> > Best,
> >
> > Iuri.
> >
> > ______________________________________________
> > R-help at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
> 
> 
> 
> -- 
> Joris Meys
> Statistical consultant
> 
> Ghent University
> Faculty of Bioscience Engineering
> Department of Applied mathematics, biometrics and process control
> 
> tel : +32 9 264 59 87
> Joris.Meys at Ugent.be
> -------------------------------
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> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>