[R] re placing values in a matrix

[Gabor Csardi]

Derek, 

the 0*m part zeros out everything in the matrix, expect for the NA's, 
0*NA=NA by definition. If we add this to the y[ col(m) ] matrix, then
NA+anything=NA, but 0+anything=anything.

G.

ps. please answer to the list (as well)

On Fri, Feb 01, 2008 at 08:52:50AM -0500, Derek Cyr wrote:
> 
> 
> Thank you, that works very nicely.  I am a little curious as to why you
> need to do 0*m and add that to y[col(m)] in the second expression.  It
> works perfectly, but I am just not sure how, lol.  Thanks
> 
> D

[...]

> Actually, you don't need apply. If there are no NA's then it is
> very easy:
> 
> m[] <- y[ col(m) ]
> 
> If you want to keep the NA's then it is a bit more tricky:
> 
> m[] <- 0*m + y[ col(m) ]
> 
> 
> G.
> 
> On Thu, Jan 31, 2008 at 07:03:51PM -0800, dxc13 wrote:
> >
> > useR's,
> >
> > Consider:
> > y <- c(20, 25, 30)
> > > m <- matrix(c(0.0,1,NA,0.5,1.25,0.75, 0.5, NA,
> > > NA),byrow=TRUE,nrow=3,ncol=3)
> > > m
> >      [,1] [,2] [,3]
> > [1,]  0.0 1.00   NA
> > [2,]  0.5 1.25 0.75
> > [3,]  0.5   NA   NA
> >
> > For each numeric value, I want to replace them with their corresponding
> > y-value.  The result should look like (here, each row represents a
> variable
> > rather than the columns):
> >       [,1] [,2] [,3]
> > [1,]  20   25   NA
> > [2,]  20   25   30
> > [3,]  20  NA   NA
> >
> > Does anyone know how I can do this using apply()?  Or is there an easier
> > way?  Thanks in advance.
> >
> > Derek
> > --
> > View this message in context:
> http://www.nabble.com/replacing-values-in-a-matrix-tp15219764p15219764.html
> > Sent from the R help mailing list archive at Nabble.com.
> >
> > ______________________________________________
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> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> 
> --
> Csardi Gabor <csardi at rmki.kfki.hu>    UNIL DGM
> 
> 
> 
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-- 
Csardi Gabor <csardi at rmki.kfki.hu>    UNIL DGM