Le 25/04/2023 à 17:39, Bill Dunlap a écrit :
x <- c(1, 1, 2, 2, 2, 3)
y <- c(1, 2, 1, 3, NA, 3)
str(xyTable(x,y))
List of 3
$ x : num [1:6] 1 1 2 2 NA 3
$ y : num [1:6] 1 2 1 3 NA 3
$ number: int [1:6] 1 1 1 NA NA 1
How many (2,3)s do we have? At least one, the third entry, but the fourth
entry, (2,NA), is possibly a (2,3) so we don't know and make the count NA.
I suspect this is not the intended logic, but a byproduct of finding value
changes in a sorted vector with the idiom x[-1]!=x[-length(x). Also the
following does follow that logic:
x <- c(1, 1, 2, 2, 5, 6)
y <- c(2, 2, 2, 4, NA, 3)
str(xyTable(x,y))
List of 3
$ x : num [1:5] 1 2 2 5 6
$ y : num [1:5] 2 2 4 NA 3
$ number: int [1:5] 2 1 1 1 1
Not really. If we take
x <- c(1, 1, 2, 2, 5, 6, 5, 5)
y <- c(2, 2, 2, 4, NA, 3, 3, 4)
we get
str(xyTable(x,y))
List of 3
$ x : num [1:7] 1 2 2 5 5 NA 6
$ y : num [1:7] 2 2 4 3 4 NA 3
$ number: int [1:7] 2 1 1 1 NA NA 1
How many (5, 3) we have? At least 1 but (5, NA) is possibly (5,3) so we
should have NA but we have 1.
How many (5, 4) we have? At least 1 but (5, NA) is possibly (5,4) and we
do get NA. So restored logic is not consistent.
Without talking about a pair (NA, NA) appeared and not producing (5, NA)
pair.
Best,
Serguei.
table() does not use this logic, as one NA in a vector would make all the
counts NA. Should xyTable have a way to handle NAs the way table() does?
-Bill
On Tue, Apr 25, 2023 at 1:26 AM Viechtbauer, Wolfgang (NP) <
wolfgang.viechtba...@maastrichtuniversity.nl> wrote:
Hi all,
Posted this many years ago (
https://stat.ethz.ch/pipermail/r-devel/2017-December/075224.html), but
either this slipped under the radar or my feeble mind is unable to
understand what xyTable() is doing here and nobody bothered to correct me.
I now stumbled again across this issue.
x <- c(1, 1, 2, 2, 2, 3)
y <- c(1, 2, 1, 3, NA, 3)
table(x, y, useNA="always")
xyTable(x, y)
Why does xyTable() report that there are NA instances of (2,3)? I could
understand the logic that the NA could be anything, including a 3, so the
$number value for (2,3) is therefore unknown, but then the same should
apply so (2,1), but here $number is 1, so the logic is then inconsistent.
I stared at the xyTable code for a while and I suspect this is coming from
order() using na.last=TRUE by default, but in any case, to me the behavior
above is surprising.
Best,
Wolfgang
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