m...@celos.net wrote:
Arrays of POSIXlt dates always return a length of 9. This
is correct (they're really lists of vectors of seconds,
hours, and so forth), but other methods disguise them as
flat vectors, giving superficially surprising behaviour:
strings <- paste('2009-1-', 1:31, sep='')
dates <- strptime(strings, format="%Y-%m-%d")
print(dates)
# [1] "2009-01-01" "2009-01-02" "2009-01-03" "2009-01-04" "2009-01-05"
# [6] "2009-01-06" "2009-01-07" "2009-01-08" "2009-01-09" "2009-01-10"
# [11] "2009-01-11" "2009-01-12" "2009-01-13" "2009-01-14" "2009-01-15"
# [16] "2009-01-16" "2009-01-17" "2009-01-18" "2009-01-19" "2009-01-20"
# [21] "2009-01-21" "2009-01-22" "2009-01-23" "2009-01-24" "2009-01-25"
# [26] "2009-01-26" "2009-01-27" "2009-01-28" "2009-01-29" "2009-01-30"
# [31] "2009-01-31"
print(length(dates))
# [1] 9
str(dates)
# POSIXlt[1:9], format: "2009-01-01" "2009-01-02" "2009-01-03" "2009-01-04"
...
print(dates[20])
# [1] "2009-01-20"
print(length(dates[20]))
# [1] 9
I've since realised that POSIXct makes date vectors easier,
but could we also have something like:
length.POSIXlt <- function(x) { length(x$sec) }
in datetime.R, to avoid breaking functions (like the
str.POSIXt method) which use length() in this way?
[You need "wishlist" in the title for this sort of stuff.]
I'd be wary of this. Just the other day we found that identical() broke
on some objects because a package had length() redefined as a class
method. I.e. the danger is that something wants to use length() with its
original low-level interpretation.
Thanks,
Mark <><
------
Version:
platform = i686-pc-linux-gnu
arch = i686
os = linux-gnu
system = i686, linux-gnu
status =
major = 2
minor = 10.0
year = 2009
month = 10
day = 26
svn rev = 50208
language = R
version.string = R version 2.10.0 (2009-10-26)
Locale:
C
Search Path:
.GlobalEnv, package:stats, package:graphics, package:grDevices, package:utils,
package:datasets, package:methods, Autoloads, package:base
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