learning R

I was wondering why the following doesn't work:

a=c(1,2)
names(a)=c("one","two")
a

one two
 1   2

names(a[2])

[1] "two"

names(a[2])="too"
names(a)

[1] "one" "two"

a

one two
 1   2

I must not be understanding some basic concept here.
Why doesn't the 2nd name change to "too"?

I cannot tell you why, perhaps you are not actually working with the  
names of a, but I can show you that:

 > names(a)[2] <- "too"
 > a[2]
too
   2
 > a
one too
   1   2

And this is seen as well in the help page examples. The help page also  
says the following, which I cannot understand:

It is possible to update just part of the names attribute via the  
general rules: see the examples. This works because the expression  
there is evaluated as z <- "names<-"(z, "[<-"(names(z), 3, "c2")).

also unrelated:  if I have two vectors and I want to combine them to  
form a matrix ,is cbind (or rbind) the most direct way to do this?

e.g.

x=c(1,2,3)
y=c(3,4,5)
z=rbind(x,y)

That is ok. Also effective would be:

z <- matrix( c(x,y), ncol=length(x) )

alternatively: is there a way to make a matrix with dim=2,3 and then  
to replace the 2nd row with y

something like this (which doesn't work but perhaps there is another  
way to do the equivalent?)

attr(x,"dim")=c(2,3)
x[2,]=y

Not sure why you are trying to do that to x since it is a vector but  
it can be done if you make it a matrix first. Take a look at these and  
see if you can figure out what is happening:

 > x <- matrix(x,2,3)  # second and third arguments of matrix function  
are nrow and ncol.
 > x
      [,1] [,2] [,3]
[1,]    1    3    2
[2,]    2    1    3

And then try:
 > x = c(1,2,3)
 > x <- matrix(x,2,3,byrow=TRUE)
 > x
      [,1] [,2] [,3]
[1,]    1    2    3
[2,]    1    2    3

And now that x is a matrix, this will work:

 > x[2,] <- y
 > x
      [,1] [,2] [,3]
[1,]    1    2    3
[2,]    3    4    5

-- David Winsemius

______________________________________________
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.