Le 25/04/2023 à 10:24, Viechtbauer, Wolfgang (NP) a écrit :
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 $number is 1, so the logic is then inconsistent.
I stared at the xyTable code for a while and I suspect this is coming from
order() using na.last=TRUE by default, but in any case, to me the behavior
above is surprising.
Not really. The variable 'first' in xyTable() is supposed to detect
positions of first values in repeated pair sequences. Then it is used to
retained only their indexes in a vector of type 1:n. Finally, by taking
diff(), a number of repeated pairs is obtained. However, as 'first' will
contain one NA for your example, the diff() call will produce two NAs
by taking the difference with precedent and following number. Hence, the
result.
Here is a slightly modified code ox xyTable to handle NA too.
xyTableNA <- function (x, y = NULL, digits)
{
x <- xy.coords(x, y, setLab = FALSE)
y <- signif(x$y, digits = digits)
x <- signif(x$x, digits = digits)
n <- length(x)
number <- if (n > 0) {
orderxy <- order(x, y)
x <- x[orderxy]
y <- y[orderxy]
first <- c(TRUE, (x[-1L] != x[-n]) | (y[-1L] != y[-n]))
firstNA <- c(TRUE, xor(is.na(x[-1L]), is.na(x[-n])) |
xor(is.na(y[-1L]), is.na(y[-n])))
first[firstNA] <- TRUE
first[is.na(first) | isFALSE(first)] <- FALSE
x <- x[first]
y <- y[first]
diff(c((1L:n)[first], n + 1L))
}
else integer()
list(x = x, y = y, number = number)
}
Best,
Serguei.
Best,
Wolfgang
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