Is it documented anywhere that factors may lose their ordered-ness when
used as keys? E.g.
library("data.table")
F <- factor(LETTERS[1:3], levels = rev(LETTERS), ordered = TRUE)
X<- data.table(A = F, B = F, key = "A")
str(X) # A is no longer ordered; B still is
stopifnot(is.ordered(X$B)) # OK
stopifnot(is.ordered(X$A)) # Fails!
I can kind of see why it might happen, but it still caught me by
surprise, and if it ever happens on (some?) ad-hoc index lookups then it
will really cause bugs in my code....
Allan
(Above is simpler version of example sent off-list to Matthew)
> sessionInfo()
R version 2.13.0 (2011-04-13)
Platform: x86_64-unknown-linux-gnu (64-bit)
locale:
[1] LC_CTYPE=en_GB.utf8 LC_NUMERIC=C
[3] LC_TIME=en_GB.utf8 LC_COLLATE=en_GB.utf8
[5] LC_MONETARY=C LC_MESSAGES=en_GB.utf8
[7] LC_PAPER=en_GB.utf8 LC_NAME=C
[9] LC_ADDRESS=C LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_GB.utf8 LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] data.table_1.6 ctv_0.7-2
loaded via a namespace (and not attached):
[1] tools_2.13.0
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