[R] matrix and a function - apply function

[Petr PIKAL]

Hi


r-help-bounces at r-project.org napsal dne 02.02.2011 16:05:21:

> 
> On Feb 2, 2011, at 9:12 AM, ADias wrote:
> 
> >
> > Hi
> >
> > I have this function and this matrix:
> >
> > function(x,y) x+y/x
> >
> > m<-matrix(c(1,2,4,2,10,8),3,2)
> >
> >> m
> >     [,1] [,2]
> > [1,]    1    2
> > [2,]    2   10
> > [3,]    4    8
> >
> > each row represent a point (x,y) in a chart and I want via my 
> > fucntion to
> > calculate the image in order to get this results:
> >
> > for point (1,2) I would get 1+2/1 = 3
> > for point (2,10) I would get 2+10/2 = 7
> > for point (4,8) I would get 4+8/4 = 6
> >
> > I have tried using sapply here but I get this:
> >
> >> sapply(m,function(x,y) x+y/x)
> > Error in y/x : 'y' is missing
> 
> I'm not sure what sapply does with a matrix argument. I've only used t 
> with vectors and lists.  I suspect that it would straighten out the 
> argument to a length = 6 vector. (And then, of course, the "y" 
> wouldn't be there.)
> 
> 
> >
> > what I am doing wrong?
> 
> Two things: instead use apply() and realize that the argument is 
> passed as a vector
> 
> apply(m, 1, function(x) x[1] +x[2]/x[1] )

Maybe apply is not necessary here

> m[,1]+m[,2]/m[,1]
[1] 3 7 6

Regards
Petr


> 
> 
> -- 
> David Winsemius, MD
> West Hartford, CT
> 
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