On 02/09/2009 6:50 PM, Tony Plate wrote:
Duncan Murdoch wrote:
On 02/09/2009 4:10 PM, Stavros Macrakis wrote:
Let us stipulate that the current wording can be construed to be
correct.
I'd rather just state that the current wording is correct, without the
weasel words.
I would nonetheless claim that the documentation as currently written
is at best ambiguous and confusing, and would benefit from improved
wording.
A claim that documentation would benefit from improved wording is a
tautology. A claim that the documentation is ambiguous requires more
evidence than you've offered. You have demonstrated that someone
could be confused when reading it, but that isn't necessarily our
responsibility.
Duncan Murdoch
I suspect the confusion comes from the mistaken, but very
understandable, interpretation that the phrase "'x' is a vector" in the
documentation should somehow equate with the R function call
'is.vector(x)'. Similar potentially misleading wording appears in the
"Description" for ?is.vector:
"|is.vector| returns |TRUE| if |x| is a vector (of mode logical,
integer, real, complex, character, raw or list if not specified) or
expression and |FALSE|".
However, the Details for ?is.vector do clarify, saying:
"|is.vector| returns |FALSE| if |x| has any attributes except names."
Here are some concrete suggestions for improving the documentation:
(1) In the Details or Note section for ?is.atomic, add the paragraph:
"is.atomic is unaffected by the presence of attributes on 'x', unlike
is.vector (which would probably be better named is.bare.vector).
is.atomic(x) merely tests whether the data mode of x is an atomic vector
type, and ignores whether or not x has attributes. The behavior of
is.vector(x) is quite different -- it tests whether x is a bare vector.
is.vector can be TRUE for lists and expressions as well as atomic vector
types, but if there are attributes other than names on x, is.vector(x)
returns FALSE."
(2) In the Description section for ?is.vector, change
"|is.vector| returns |TRUE| if |x| is a vector (of mode logical,
integer, real, complex, character, raw or list if not specified) or
expression"
to
"|is.vector| returns |TRUE| if |x| is a bare vector (of mode logical,
integer, real, complex, character, raw or list if not specified, with no
attributes other than names), or expression with no attributes other
than names"
Thanks for the suggestions. I don't like your first one for a number of
reasons: too wordy, not quite right in its description of is.vector,
editorializing about some other function's name, etc. I'd rather leave
the ?is.atomic page alone.
I agree that the ?is.vector page should be improved, but your suggestion
is ambiguous: does the "no attributes" part apply only to expressions?
I've just spent a few minutes, and come up with the following rewrite.
I'd shorten the Description entry to
\code{is.vector} returns \code{TRUE} if \code{x} is a vector of the
specified mode having no attributes other than names. It returns
\code{FALSE} otherwise.
and lengthen the Details to
If \code{mode = "any"}, \code{is.vector} returns \code{TRUE} for
modes logical, integer, real, complex, character, raw, list or
expression. It returns \code{FALSE} if \code{x} has any attributes
except names. (This is incompatible with S.) On the other hand,
\code{as.vector} removes \emph{all} attributes including names for
results of atomic mode.
It's not perfect, because it is ambiguous what "This" refers to, but I
don't actually know how much of the preceding description is
incompatible with S, or even whether that claim makes sense: Are all
versions of S consistent in this? I think it's probably inappropriate
to be trying to document S here... Nevertheless, I've committed this
change.
It's not easy to write good documentation.
Duncan Murdoch
-- Tony Plate
What would be lost by that?
One could argue that in R's pre-history we should have had is.atomic
imply
is.vector, but that's not how things are documented, and I think we're
pretty much stuck with the definitions we've got on low level
functions like
those.
I explicitly said in my mail that I was not suggesting that past
design decisions (wise or unwise) be revisited; only that they be
documented more clearly.
-s
On Wed, Sep 2, 2009 at 3:37 PM, Duncan Murdoch<murd...@stats.uwo.ca>
wrote:
On 9/2/2009 2:39 PM, Stavros Macrakis wrote:
The documentation for is.atomic and is.recursive is inconsistent with
their behavior in R 2.9.1 Windows.
? is.atomic
'is.atomic' returns 'TRUE' if 'x' is an atomic vector (or 'NULL')
and 'FALSE' otherwise.
...
'is.atomic' is true for the atomic vector types ('"logical"',
'"integer"', '"numeric"', '"complex"', '"character"' and '"raw"')
and 'NULL'.
This description implies that is.atomic(x) implies is.vector(x)
(assuming that an "atomic vector type" is a subset of a "vector
type"). But in fact that is not true for values with class
attributes:
I don't see is.vector mentioned there. The description of is.vector
on its
own man page implies the behaviour below; I think the description of
is.atomic that you quote above is also consistent with the behaviour.
One could argue that in R's pre-history we should have had is.atomic
imply
is.vector, but that's not how things are documented, and I think we're
pretty much stuck with the definitions we've got on low level
functions like
those.
is.atomic(factor(3)) => TRUE
is.vector(factor(3)) => FALSE
is.atomic(table(3)) => TRUE
is.vector(factor(3)) => FALSE
It appears, then, that is.atomic requires only that unclass(x) be an
atomic vector, not that x be an atomic vector.
There is also another case where is.atomic(x) !=
is.vector(unclass(x)):
is.atomic(NULL) => TRUE
is.vector(NULL) => FALSE
It would be useful to make the documentation consistent with the
implementation. (Presumably by updating the documentation, not
changing the behavior.)
The documentation continues:
'is.recursive' returns 'TRUE' if 'x' has a recursive (list-like)
structure and 'FALSE' otherwise.
...
Most types of language objects are regarded as recursive: those
which are not are the atomic vector types, 'NULL' and symbols (as
given by 'as.name').
But is.recursive(as.name('foo')) == is.recursive(quote(foo)) == FALSE.
That's what it says should happen. symbols such as as.name('foo')
are not
recursive.
Duncan Murdoch
Again, it would be useful to make the documentation consistent with
the implementation.
To summarize all this in a table of the most common datatypes:
outerl <-
function(f, a, b)
structure(outer(a,b,Vectorize(f)),
dimnames=list(a,b))
outerl(function(x,f)(match.fun(f))(x),
list(3,factor(c("a","b")),NULL,function()3,as.name("foo"),environment()),
list("class","mode","storage.mode","is.vector","is.atomic","is.recursive"))
class mode storage.mode is.vector
is.atomic is.recursive
3 "numeric" "numeric" "double" "TRUE"
"TRUE" "FALSE" <<< OK
1:2 "factor" "numeric" "integer" "FALSE"
"TRUE" "FALSE" <<< inconsistent
NULL "NULL" "NULL" "NULL" "FALSE"
"TRUE" "FALSE" <<< inconsistent
function () "function" "function" "function" "FALSE"
"FALSE" "TRUE" <<< OK
foo "name" "name" "symbol" "FALSE"
"FALSE" "FALSE" <<< inconsistent
<environment> "environment" "environment" "environment" "FALSE"
"FALSE" "TRUE" <<< OK
Thanks,
-s
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