R devel - May 2019 - nrow(rbind(character(), character())) returns 2 (as documented but very unintuitive, IMHO)

Hi all,

Apologies if this has been asked before (a quick google didn't  find it for
me),and I know this is a case of behaving as documented but its so
unintuitive (to me at least) that I figured I'd bring it up here anyway. I
figure its probably going to not be changed,  but I'm happy to submit a
patch if this is something R-core feels can/should change.

So I recently got bitten by the fact that
> nrow(rbind(character(), character()))
[1] 2


I was checking whether the result of an rbind call had more than one row,
and that unexpected returned true, causing all sorts of shenanigans
downstream as I'm sure you can imagine.

Now I know that from ?rbind

For ?cbind? (?rbind?), vectors of zero length (including
?NULL?)
>
>      are ignored unless the result would have zero rows (columns), for
>
>      S compatibility.  (Zero-extent matrices do not occur in S3 and are
>
>      not ignored in R.)
>
But there's a couple of things here. First, for the rowbind  case this
reads as "if there would be zero columns,  the vectors will not be
ignored". This wording implies to me that not ignoring the vectors is a
remedy to the "problem" of the potential for a zero-column return, but
thats not the case.  The result still has 0 columns, it just does not also
have zero rows. So even if the behavior is not changed, perhaps this
wording can be massaged for clarity?

The other issue, which I admit is likely a problem with my intuition, but
which I don't think I'm alone in having, is that even if I can't
have a 0x0
matrix (which is what I'd prefer) I would have expected/preferred a 1x0
matrix, the reasoning being that if we must avoid a 0x0 return value, we
would do the  minimum required to avoid, which is to not ignore the first
length 0 vector, to ensure a non-zero-extent matrix, but then ignore the
remaining ones as they contain information for 0 new rows.

Of course I can program around this now that I know the behavior, but
again, its so unintuitive (even for someone with a fairly well developed
intuition for R's sometimes "quirky" behavior) that I figured
I'd bring it
up.

Thoughts?

Best,
~G

	[[alternative HTML version deleted]]

The existing behaviour seems inutitive to me. I would consider these
invariants for n vector x_i's each with size m:

* nrow(rbind(x_1, x_2, ..., x_n)) equals n
* ncol(rbind(x_1, x_2, ..., x_n)) equals m

Additionally, wouldn't you expect rbind(x_1[i], x_2[i]) to equal
rbind(x_1, x_2)[, i, drop = FALSE] ?

Hadley

On Thu, May 16, 2019 at 3:26 PM Gabriel Becker <gabembecker at gmail.com>
wrote:
>
> Hi all,
>
> Apologies if this has been asked before (a quick google didn't  find it
for
> me),and I know this is a case of behaving as documented but its so
> unintuitive (to me at least) that I figured I'd bring it up here
anyway. I
> figure its probably going to not be changed,  but I'm happy to submit a
> patch if this is something R-core feels can/should change.
>
> So I recently got bitten by the fact that
>
> > nrow(rbind(character(), character()))
>
> [1] 2
>
>
> I was checking whether the result of an rbind call had more than one row,
> and that unexpected returned true, causing all sorts of shenanigans
> downstream as I'm sure you can imagine.
>
> Now I know that from ?rbind
>
> For ?cbind? (?rbind?), vectors of zero length (including ?NULL?)
> >
> >      are ignored unless the result would have zero rows (columns), for
> >
> >      S compatibility.  (Zero-extent matrices do not occur in S3 and
are
> >
> >      not ignored in R.)
> >
>
> But there's a couple of things here. First, for the rowbind  case this
> reads as "if there would be zero columns,  the vectors will not be
> ignored". This wording implies to me that not ignoring the vectors is
a
> remedy to the "problem" of the potential for a zero-column
return, but
> thats not the case.  The result still has 0 columns, it just does not also
> have zero rows. So even if the behavior is not changed, perhaps this
> wording can be massaged for clarity?
>
> The other issue, which I admit is likely a problem with my intuition, but
> which I don't think I'm alone in having, is that even if I
can't have a 0x0
> matrix (which is what I'd prefer) I would have expected/preferred a 1x0
> matrix, the reasoning being that if we must avoid a 0x0 return value, we
> would do the  minimum required to avoid, which is to not ignore the first
> length 0 vector, to ensure a non-zero-extent matrix, but then ignore the
> remaining ones as they contain information for 0 new rows.
>
> Of course I can program around this now that I know the behavior, but
> again, its so unintuitive (even for someone with a fairly well developed
> intuition for R's sometimes "quirky" behavior) that I figured
I'd bring it
> up.
>
> Thoughts?
>
> Best,
> ~G
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel


-- 
http://hadley.nz

Gabriel, you ask an insightful and instructive question. One of R's
great strengths is that we have a forum where this kind of edge-case
can be fruitfully discussed.
My interest in this would be the names of the arguments; in the magic
package I make heavy use of the dimnames of zero-extent arrays.
> rbind(a='x',b='y')
  [,1]
a "x"
b "y"
> rbind(a='x',b=character())
  [,1]
a "x"
> rbind(a=character(),b=character())
a
b

The first and third idiom are fine.  The result of the second one, in
which we rbind() a length-one to  a length-zero vector, is desirable
IMO on the grounds that the content of a two-row matrix cannot be
defined sensibly, so R takes the perfectly reasonable stance of
deciding to ignore the second argument...which carries with it the
implication that the name ('b')  be ignored too.  If the second
argument *could* be recycled, I would want the name, otherwise I
wouldn't.  And this is what R does.

best wishes,


hankin.robin at gmail.com



hankin.robin at gmail.com




On Fri, May 17, 2019 at 9:06 AM Hadley Wickham <h.wickham at gmail.com>
wrote:
>
> The existing behaviour seems inutitive to me. I would consider these
> invariants for n vector x_i's each with size m:
>
> * nrow(rbind(x_1, x_2, ..., x_n)) equals n
> * ncol(rbind(x_1, x_2, ..., x_n)) equals m
>
> Additionally, wouldn't you expect rbind(x_1[i], x_2[i]) to equal
> rbind(x_1, x_2)[, i, drop = FALSE] ?
>
> Hadley
>
> On Thu, May 16, 2019 at 3:26 PM Gabriel Becker <gabembecker at
gmail.com> wrote:
> >
> > Hi all,
> >
> > Apologies if this has been asked before (a quick google didn't 
find it for
> > me),and I know this is a case of behaving as documented but its so
> > unintuitive (to me at least) that I figured I'd bring it up here
anyway. I
> > figure its probably going to not be changed,  but I'm happy to
submit a
> > patch if this is something R-core feels can/should change.
> >
> > So I recently got bitten by the fact that
> >
> > > nrow(rbind(character(), character()))
> >
> > [1] 2
> >
> >
> > I was checking whether the result of an rbind call had more than one
row,
> > and that unexpected returned true, causing all sorts of shenanigans
> > downstream as I'm sure you can imagine.
> >
> > Now I know that from ?rbind
> >
> > For ?cbind? (?rbind?), vectors of zero length (including ?NULL?)
> > >
> > >      are ignored unless the result would have zero rows
(columns), for
> > >
> > >      S compatibility.  (Zero-extent matrices do not occur in S3
and are
> > >
> > >      not ignored in R.)
> > >
> >
> > But there's a couple of things here. First, for the rowbind  case
this
> > reads as "if there would be zero columns,  the vectors will not
be
> > ignored". This wording implies to me that not ignoring the
vectors is a
> > remedy to the "problem" of the potential for a zero-column
return, but
> > thats not the case.  The result still has 0 columns, it just does not
also
> > have zero rows. So even if the behavior is not changed, perhaps this
> > wording can be massaged for clarity?
> >
> > The other issue, which I admit is likely a problem with my intuition,
but
> > which I don't think I'm alone in having, is that even if I
can't have a 0x0
> > matrix (which is what I'd prefer) I would have expected/preferred
a 1x0
> > matrix, the reasoning being that if we must avoid a 0x0 return value,
we
> > would do the  minimum required to avoid, which is to not ignore the
first
> > length 0 vector, to ensure a non-zero-extent matrix, but then ignore
the
> > remaining ones as they contain information for 0 new rows.
> >
> > Of course I can program around this now that I know the behavior, but
> > again, its so unintuitive (even for someone with a fairly well
developed
> > intuition for R's sometimes "quirky" behavior) that I
figured I'd bring it
> > up.
> >
> > Thoughts?
> >
> > Best,
> > ~G
> >
> >         [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
>
>
>
> --
> http://hadley.nz
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

Hi Hadley,

Thanks for the counterpoint. Response below.

On Thu, May 16, 2019 at 1:59 PM Hadley Wickham <h.wickham at gmail.com>
wrote:
> The existing behaviour seems inutitive to me. I would consider these
> invariants for n vector x_i's each with size m:
>
> * nrow(rbind(x_1, x_2, ..., x_n)) equals n
>
Personally, no I wouldn't. I would consider m==0 a degenerate case, where
there is no data, but I personally find matrices (or data.frames) with rows
but no columns a very strange concept. The converse is not true, I
understand the utility of columns but no rows, particularly in the
data.frame case, but rows with no columns are observations we didn't
observe anything about. Strange, imho.

Also, I know that you said *each with size m*, but the generalization would
be

for n vectors with m = max(length(x_i))
nrow(rbind(x_1, ..., x_n)) = m

And that is the behavior now as documented, but *only* when length(x_i) >0
for all i (or, currently, when m == 0, so all vectors are length 0).
> nrow(rbind(1:5, numeric()))
[1] 1


So that is where I was coming from. Length-zero vectors don't add rows
because they contain no observed information.

I do see where you'er coming from, but it does make interrogating
nrow(rbind(x_1, ..., x_n)) NOT mean  (give me the number of observations
for which I have data), which is what it means in non-degenerate contexts,
and that seems pretty important too.

Robin does also have an interesting point below about argument names, but
I'll leave that for another mail.

Best,
~G

	[[alternative HTML version deleted]]

Hi Gabe,

 ? ncol(data.frame(aa=c("a", "b", "c"),
AA=c("A", "B", "C")))
 ? # [1] 2

 ? ncol(data.frame(aa="a", AA="A"))
 ? # [1] 2

 ? ncol(data.frame(aa=character(0), AA=character(0)))
 ? # [1] 2

 ? ncol(cbind(aa=c("a", "b", "c"),
AA=c("A", "B", "C")))
 ? # [1] 2

 ? ncol(cbind(aa="a", AA="A"))
 ? # [1] 2

 ? ncol(cbind(aa=character(0), AA=character(0)))
 ? # [1] 2

 ? nrow(rbind(aa=c("a", "b", "c"),
AA=c("A", "B", "C")))
 ? # [1] 2

 ? nrow(rbind(aa="a", AA="A"))
 ? # [1] 2

 ? nrow(rbind(aa=character(0), AA=character(0)))
 ? # [1] 2

hmmm... not sure why ncol(cbind(aa=character(0), AA=character(0))) or 
nrow(rbind(aa=character(0), AA=character(0))) should do anything 
different from what they do.

In my experience, and more generally speaking, the desire to treat 
0-length vectors as a special case that deviates from the 
non-zero-length case has never been productive.

H.


On 5/16/19 13:17, Gabriel Becker wrote:
> Hi all,
>
> Apologies if this has been asked before (a quick google didn't  find it
for
> me),and I know this is a case of behaving as documented but its so
> unintuitive (to me at least) that I figured I'd bring it up here
anyway. I
> figure its probably going to not be changed,  but I'm happy to submit a
> patch if this is something R-core feels can/should change.
>
> So I recently got bitten by the fact that
>
>> nrow(rbind(character(), character()))
> [1] 2
>
>
> I was checking whether the result of an rbind call had more than one row,
> and that unexpected returned true, causing all sorts of shenanigans
> downstream as I'm sure you can imagine.
>
> Now I know that from ?rbind
>
> For ?cbind? (?rbind?), vectors of zero length (including ?NULL?)
>>       are ignored unless the result would have zero rows (columns), for
>>
>>       S compatibility.  (Zero-extent matrices do not occur in S3 and
are
>>
>>       not ignored in R.)
>>
> But there's a couple of things here. First, for the rowbind  case this
> reads as "if there would be zero columns,  the vectors will not be
> ignored". This wording implies to me that not ignoring the vectors is
a
> remedy to the "problem" of the potential for a zero-column
return, but
> thats not the case.  The result still has 0 columns, it just does not also
> have zero rows. So even if the behavior is not changed, perhaps this
> wording can be massaged for clarity?
>
> The other issue, which I admit is likely a problem with my intuition, but
> which I don't think I'm alone in having, is that even if I
can't have a 0x0
> matrix (which is what I'd prefer) I would have expected/preferred a 1x0
> matrix, the reasoning being that if we must avoid a 0x0 return value, we
> would do the  minimum required to avoid, which is to not ignore the first
> length 0 vector, to ensure a non-zero-extent matrix, but then ignore the
> remaining ones as they contain information for 0 new rows.
>
> Of course I can program around this now that I know the behavior, but
> again, its so unintuitive (even for someone with a fairly well developed
> intuition for R's sometimes "quirky" behavior) that I figured
I'd bring it
> up.
>
> Thoughts?
>
> Best,
> ~G
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
>
https://urldefense.proofpoint.com/v2/url?u=https-3A__stat.ethz.ch_mailman_listinfo_r-2Ddevel&d=DwIFaQ&c=eRAMFD45gAfqt84VtBcfhQ&r=BK7q3XeAvimeWdGbWY_wJYbW0WYiZvSXAJJKaaPhzWA&m=WzRf-6PuyYeprM0v55lLX2U-_hYGf__5yf3h6JNdJH0&s=nn76KQtp4viR66768zoSNcH7WpG77Pp8LyhOwYOs674&e
-- 
Herv? Pag?s

Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024

E-mail: hpages at fredhutch.org
Phone:  (206) 667-5791
Fax:    (206) 667-1319

Hi Herve,

Inline.



On Thu, May 16, 2019 at 4:45 PM Pages, Herve <hpages at fredhutch.org>
wrote:
> Hi Gabe,
>
>    ncol(data.frame(aa=c("a", "b", "c"),
AA=c("A", "B", "C")))
>    # [1] 2
>
>    ncol(data.frame(aa="a", AA="A"))
>    # [1] 2
>
>    ncol(data.frame(aa=character(0), AA=character(0)))
>    # [1] 2
>
>    ncol(cbind(aa=c("a", "b", "c"),
AA=c("A", "B", "C")))
>    # [1] 2
>
>    ncol(cbind(aa="a", AA="A"))
>    # [1] 2
>
>    ncol(cbind(aa=character(0), AA=character(0)))
>    # [1] 2
>
>    nrow(rbind(aa=c("a", "b", "c"),
AA=c("A", "B", "C")))
>    # [1] 2
>
>    nrow(rbind(aa="a", AA="A"))
>    # [1] 2
>
>    nrow(rbind(aa=character(0), AA=character(0)))
>    # [1] 2
>
Sure, but
> nrow(rbind(aa = c("a", "b", "c"), AA =
c("a", "b", "c")))
[1] 2
> nrow(rbind(aa = c("a", "b", "c"), AA =
"a"))
[1] 2
> nrow(rbind(aa = c("a", "b", "c"), AA =
character()))
[1] 1

So even if I ultimately "lose"  this debate (which really wouldn't
shock
me, even if R-core did agree with me there's backwards compatibility to
consider), you have to concede that the current behavior is more
complicated than the above is acknowledging.

By rights of the invariance that you and Hadley are advocating,  as far as
I understand it, the last should give 2 rows, one of which is all NAs,
rather than giving only one row as it currently does (and, I assume?,
always has).

So there are two different behavior patterns that could coherently (and
internally-consistently) be generalized to apply to the  rbind(character(),
character()) case, not just one. I'm making the case that the other one
(that length 0 vectors do not add rows because they don't contain data)
would be equally valid, and to N>1 people, at least equally intuitive.

Best,
~G
>
> hmmm... not sure why ncol(cbind(aa=character(0), AA=character(0))) or
> nrow(rbind(aa=character(0), AA=character(0))) should do anything
> different from what they do.
>
> In my experience, and more generally speaking, the desire to treat
> 0-length vectors as a special case that deviates from the
> non-zero-length case has never been productive.
>
> H.
>
>
> On 5/16/19 13:17, Gabriel Becker wrote:
> > Hi all,
> >
> > Apologies if this has been asked before (a quick google didn't 
find it
> for
> > me),and I know this is a case of behaving as documented but its so
> > unintuitive (to me at least) that I figured I'd bring it up here
anyway.
> I
> > figure its probably going to not be changed,  but I'm happy to
submit a
> > patch if this is something R-core feels can/should change.
> >
> > So I recently got bitten by the fact that
> >
> >> nrow(rbind(character(), character()))
> > [1] 2
> >
> >
> > I was checking whether the result of an rbind call had more than one
row,
> > and that unexpected returned true, causing all sorts of shenanigans
> > downstream as I'm sure you can imagine.
> >
> > Now I know that from ?rbind
> >
> > For ?cbind? (?rbind?), vectors of zero length (including ?NULL?)
> >>       are ignored unless the result would have zero rows
(columns), for
> >>
> >>       S compatibility.  (Zero-extent matrices do not occur in S3
and are
> >>
> >>       not ignored in R.)
> >>
> > But there's a couple of things here. First, for the rowbind  case
this
> > reads as "if there would be zero columns,  the vectors will not
be
> > ignored". This wording implies to me that not ignoring the
vectors is a
> > remedy to the "problem" of the potential for a zero-column
return, but
> > thats not the case.  The result still has 0 columns, it just does not
> also
> > have zero rows. So even if the behavior is not changed, perhaps this
> > wording can be massaged for clarity?
> >
> > The other issue, which I admit is likely a problem with my intuition,
but
> > which I don't think I'm alone in having, is that even if I
can't have a
> 0x0
> > matrix (which is what I'd prefer) I would have expected/preferred
a 1x0
> > matrix, the reasoning being that if we must avoid a 0x0 return value,
we
> > would do the  minimum required to avoid, which is to not ignore the
first
> > length 0 vector, to ensure a non-zero-extent matrix, but then ignore
the
> > remaining ones as they contain information for 0 new rows.
> >
> > Of course I can program around this now that I know the behavior, but
> > again, its so unintuitive (even for someone with a fairly well
developed
> > intuition for R's sometimes "quirky" behavior) that I
figured I'd bring
> it
> > up.
> >
> > Thoughts?
> >
> > Best,
> > ~G
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-devel at r-project.org mailing list
> >
>
https://urldefense.proofpoint.com/v2/url?u=https-3A__stat.ethz.ch_mailman_listinfo_r-2Ddevel&d=DwIFaQ&c=eRAMFD45gAfqt84VtBcfhQ&r=BK7q3XeAvimeWdGbWY_wJYbW0WYiZvSXAJJKaaPhzWA&m=WzRf-6PuyYeprM0v55lLX2U-_hYGf__5yf3h6JNdJH0&s=nn76KQtp4viR66768zoSNcH7WpG77Pp8LyhOwYOs674&e>
> --
> Herv? Pag?s
>
> Program in Computational Biology
> Division of Public Health Sciences
> Fred Hutchinson Cancer Research Center
> 1100 Fairview Ave. N, M1-B514
> P.O. Box 19024
> Seattle, WA 98109-1024
>
> E-mail: hpages at fredhutch.org
> Phone:  (206) 667-5791
> Fax:    (206) 667-1319
>
>
	[[alternative HTML version deleted]]