learning R

a quick follow-up:

    e = new.env()
    e$a = 1
    names(e)
    # NULL
    names(e) = 'a'
    # error in names(e) = "foo" : names() applied to a non-vector

this is surprising.  names(e) 'works', there is no complaint, but when
names<- is used, the error is about the use of names, not names<-.

btw. ?names says:

"Description:

     Functions to get or set the names of an object.

Usage:

     names(x)
     names(x) <- value

Arguments:

       x: an R object.
"

and there is no clarification in the rest of the page that x cannot be
an environment, or that it has to be a vector.  furthermore:

    p = pairlist(a=1)
    names(p)
    # "a"
    names(p) = 'b'
    # fine
    is.vector(p)
    # FALSE

which is incoherent with the above error message, in that p is *not* a
vector.

vQ

the following:

    names(a[2]) = 'foo'

has (partially) a functional flavour, in that you assign to the names of
a *copy* of a part of a, while

    names(a)[2] = 'foo'

does not have the flavour, in that you assign to the names of a;  it
seems, according to the man page you quote, to be equivalent to:

    a = 'names<-'(a, '[<-.'(names(a), 2, 'foo'))

which proceeds as follows:

    tmp1 = names(a)
    # get a copy of the names of a, no effect on a

    tmp2 = '[<-'(tmp1, 2, 'foo')
    # get a copy of tmp1 with the second element replaced with 'foo'
    # no effect on either a or tmp1

    tmp3 = 'names<-'(a, tmp2)
    # get a copy of a with its names replaced with tmp2
    # no effect on either a, tmp1, or tmp2

    a = tmp3
    # backassign the result to a