R help - Feb 2004 - column names in matrix vs. data frame in R 1.8

Is the difference in behavior below, introduced in 1.8, inconsistent or,
at least, undesirable?  I couldn't find this in the NEWS.

On the one hand,
> a <- matrix (1:4, nrow=2)
> a <- data.frame (a)
> names (a) <- c("break","next")
> names (a)
[1] "break" "next"

On the other,
> a <- matrix (1:4, nrow=2)
> dimnames(a) <- list (1:2, c("break","next"))
> a <- data.frame (a)
> names(a)
[1] "break." "next."

thanks,
Denis

White.Denis at epamail.epa.gov writes:
> Is the difference in behavior below, introduced in 1.8, inconsistent or,
> at least, undesirable?  I couldn't find this in the NEWS.
> 
> On the one hand,
> 
> > a <- matrix (1:4, nrow=2)
> > a <- data.frame (a)
> > names (a) <- c("break","next")
> > names (a)
> [1] "break" "next"
> 
> On the other,
> 
> > a <- matrix (1:4, nrow=2)
> > dimnames(a) <- list (1:2, c("break","next"))
> > a <- data.frame (a)
> > names(a)
> [1] "break." "next."
Works fine if you don't use keywords as column names
> a <- matrix (1:4, nrow=2)
> dimnames(a) <- list (1:2, c("foo","bar"))
> b <- data.frame(a)
> names(b)
[1] "foo" "bar"

The difference in the result for your example has to do with an extra
step in the second case to obtain a legitimate name that can be used
with the $ operator.  R generates a syntax error for

a$break

but not for 

a$break.

> White.Denis at epamail.epa.gov writes:
>
> > Is the difference in behavior below, introduced in 1.8, inconsistent
or,
> > at least, undesirable?  I couldn't find this in the NEWS.
> >
> > On the one hand,
> >
> > > a <- matrix (1:4, nrow=2)
> > > a <- data.frame (a)
> > > names (a) <- c("break","next")
> > > names (a)
> > [1] "break" "next"
> >
> > On the other,
> >
> > > a <- matrix (1:4, nrow=2)
> > > dimnames(a) <- list (1:2,
c("break","next"))
> > > a <- data.frame (a)
> > > names(a)
> > [1] "break." "next."
>
> Works fine if you don't use keywords as column names
>
> > a <- matrix (1:4, nrow=2)
> > dimnames(a) <- list (1:2, c("foo","bar"))
> > b <- data.frame(a)
> > names(b)
> [1] "foo" "bar"
>
> The difference in the result for your example has to do with an extra
> step in the second case to obtain a legitimate name that can be used
> with the $ operator.  R generates a syntax error for
>
> a$break
>
> but not for
>
> a$break.
Ok, I'll regard it as an inconsistency that the conversion of dimnames
to data frame column names changes reserved words to legitimate names
but direct assignment doesn't.

...
> > Ok, I'll regard it as an inconsistency that the conversion of
dimnames
> > to data frame column names changes reserved words to legitimate
names
> > but direct assignment doesn't.
>
> It's not inconsistent.  data.frame has an argument `check.names' to
> control the behaviour on *creating* a data frame, and you didn't
consult
> the documentation.  Using the function names<- on the list underlying
the
> data frame does not know or care it is applied to a data frame.
After thinking about this, I guess I wonder why names<- shouldn't have
the argument 'check.names' and/or check the class of its main argument.
Why offer protection in one situation and not another?