R devel - May 2012 - Expected behaviour of is.unsorted?

Hi,

I've read ?is.unsorted and searched. Have found a few items but nothing
close, yet. Is the following expected?
> is.unsorted(data.frame(1:2))
[1] FALSE
> is.unsorted(data.frame(2:1))
[1] FALSE
> is.unsorted(data.frame(1:2,3:4))
[1] TRUE
> is.unsorted(data.frame(2:1,4:3))
[1] TRUE

IIUC, is.unsorted is intended for atomic vectors only (description of x in
?is.unsorted). Indeed the C source (src/main/sort.c) contains an error
message "only atomic vectors can be tested to be sorted". So that is
the
error message I expected to see in all cases above, since I know that
data.frame is not an atomic vector. But there is also this in
?is.unsorted: "except for atomic vectors and objects with a class (where
the >= or > method is used)" which I don't understand. Where
>= or > is
used by what, and where?

I understand why the first two are FALSE (1 item of anything must be
sorted). I don't understand the 3rd and 4th cases where length is 2:
do_isunsorted seems to call lang3(install(".gtn"), x, CADR(args))).
Does
that fall back to TRUE for some reason?

Matthew
> sessionInfo()
R version 2.15.0 (2012-03-30)
Platform: x86_64-pc-mingw32/x64 (64-bit)

locale:
[1] LC_COLLATE=English_United Kingdom.1252  LC_CTYPE=English_United
Kingdom.1252
[3] LC_MONETARY=English_United Kingdom.1252 LC_NUMERIC=C
[5] LC_TIME=English_United Kingdom.1252

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] data.table_1.8.0

loaded via a namespace (and not attached):
[1] tools_2.15.0

>> is.unsorted(data.frame(1:2))
> [1] FALSE
>> is.unsorted(data.frame(2:1))
> [1] FALSE
>> is.unsorted(data.frame(1:2,3:4))
> [1] TRUE
>> is.unsorted(data.frame(2:1,4:3))
> [1] TRUE
>
> IIUC, is.unsorted is intended for atomic vectors only (description of x in
> ?is.unsorted). Indeed the C source (src/main/sort.c) contains an error
> message "only atomic vectors can be tested to be sorted". So that
is the
> error message I expected to see in all cases above, since I know that
> data.frame is not an atomic vector. But there is also this in
> ?is.unsorted: "except for atomic vectors and objects with a class
(where
> the >= or > method is used)" which I don't understand. Where
>= or > is
> used by what, and where?
>
> I understand why the first two are FALSE (1 item of anything must be
> sorted). I don't understand the 3rd and 4th cases where length is 2:
> do_isunsorted seems to call lang3(install(".gtn"), x,
CADR(args))). Does
> that fall back to TRUE for some reason?
I've just been having similar worries with this today.  The odd
behaviour seems to be particular to data.frames.  Compare for example,

is.unsorted(list(1, 3, 2))              #NA
is.unsorted(data.frame(1, 3, 2)) #FALSE
is.unsorted(data.frame(1, 2, 3)) #TRUE

IMHO, it would be clearer if is.unsorted either always returned NA for
recursive objects of length 2 or more, or it called unlist to make it
atomic.  Either way, it should really provide some sort of warning
about non-standard input.

-- 
Regards,
Richie

live-analytics.com
4dpiecharts.com

On 12-05-23 4:37 AM, Matthew Dowle wrote:
>
> Hi,
>
> I've read ?is.unsorted and searched. Have found a few items but nothing
> close, yet. Is the following expected?
>
>> is.unsorted(data.frame(1:2))
> [1] FALSE
>> is.unsorted(data.frame(2:1))
> [1] FALSE
>> is.unsorted(data.frame(1:2,3:4))
> [1] TRUE
>> is.unsorted(data.frame(2:1,4:3))
> [1] TRUE
>
> IIUC, is.unsorted is intended for atomic vectors only (description of x in
> ?is.unsorted). Indeed the C source (src/main/sort.c) contains an error
> message "only atomic vectors can be tested to be sorted". So that
is the
> error message I expected to see in all cases above, since I know that
> data.frame is not an atomic vector. But there is also this in
> ?is.unsorted: "except for atomic vectors and objects with a class
(where
> the>= or>  method is used)" which I don't understand.
Where>= or>  is
> used by what, and where?
If you look at the source, you will see that the basic test for classed 
objects is

all(x[-1L] >= x[-length(x)])

(in the function base:::.gtn).

This comparison doesn't really makes sense for dataframes, but it does 
seem to be backwards:  that tests that x[2] >= x[1], x[3] >= x[2], etc., 
returning TRUE if all comparisons are TRUE:  but that sounds like it 
should be is.sorted(), not is.unsorted().  Or is it my brain that is 
backwards?

Duncan Murdoch

>
> I understand why the first two are FALSE (1 item of anything must be
> sorted). I don't understand the 3rd and 4th cases where length is 2:
> do_isunsorted seems to call lang3(install(".gtn"), x,
CADR(args))). Does
> that fall back to TRUE for some reason?
>
> Matthew
>
>> sessionInfo()
> R version 2.15.0 (2012-03-30)
> Platform: x86_64-pc-mingw32/x64 (64-bit)
>
> locale:
> [1] LC_COLLATE=English_United Kingdom.1252  LC_CTYPE=English_United
> Kingdom.1252
> [3] LC_MONETARY=English_United Kingdom.1252 LC_NUMERIC=C
> [5] LC_TIME=English_United Kingdom.1252
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
> other attached packages:
> [1] data.table_1.8.0
>
> loaded via a namespace (and not attached):
> [1] tools_2.15.0
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel