I've run into a problem with the datetime axis generated by axis.POSIXct.
It appears a similar issue was discussed in October 2003 under the subject line
"datetime data and plotting" (see
https://stat.ethz.ch/pipermail/r-help/2003-October/039071.html), but I
wasn't able to determine whether there is a straightforward solution.
The code below produces a graph with apparently contradictory date labels on the
top and bottom axes:
f <- "%Y/%m/%d"
d <- as.POSIXct(strptime(c("2003/1/15","2003/1/16",
"2003/1/17","2003/1/18","2003/1/19"),format=f))
plot(d,1:length(d),axes=F);box()
axis(2)
abline(v=d[3])
axis.POSIXct(1,d,format=f)
axis.POSIXct(3,at=d,format=f)
On my copy of R (I have appended the version information below my signature),
this produces a graph with a vertical line that lines up with
"2003/01/17" on the top axis, but not on the bottom axis.
The issue seems to relate to time zones: here's what d looks like on my
computer:
> d
[1] "2003-01-15 Eastern Standard Time"
[2] "2003-01-16 Eastern Standard Time"
[3] "2003-01-17 Eastern Standard Time"
[4] "2003-01-18 Eastern Standard Time"
[5] "2003-01-19 Eastern Standard Time"
(Actually I'm on Eastern Daylight Time, but let's ignore that for now.)
Changing the axes to display not only the date but also the time shows
what's going on:
f <- "%Y/%m/%d"
f2 <- "%Y-%m-%d %H:%M"
d <- as.POSIXct(strptime(c("2003/1/15","2003/1/16",
"2003/1/17","2003/1/18","2003/1/19"),format=f))
plot(d,1:length(d),axes=F);box()
axis(2)
abline(v=d[3])
axis.POSIXct(1,d,format=f2)
axis.POSIXct(3,at=d,format=f2)
The bottom axis put the ticks at 19:00 on each date. This seems an odd time
until you note that Eastern Standard Time is 5 hours behind UTC, so 19:00 EST is
00:00 UTC.
But is there any easy way to avoid this problem? It is confusing and
inconvenient that axis.POSIXct(1,d,format=f) and axis.POSIXct(3,at=d,format=f)
give seemingly contradictory scales.
Many thanks for any help!
Nick Barrowman, Ph.D.
Chief Biostatistician, Chalmers Research Group
Children's Hospital of Eastern Ontario Research Institute
401 Smyth Road, Ottawa, Ontario, K1H 8L1, Canada
Tel (613) 737-7600 ext. 3971
Fax (613) 738-4800
Email nbarrowman at cheo.on.ca
URL www.chalmersresearch.com
> version
_
platform i386-pc-mingw32
arch i386
os mingw32
system i386, mingw32
status
major 1
minor 9.0
year 2004
month 04
day 12
language R
Use the Date class rather than POSIXct since Date does not have
time zones in the first place:
d <-
as.Date(c("2003/1/15","2003/1/16","2003/1/17","2003/1/18","2003/1/19"))
plot(d,1:length(d),axes=F);box()
axis(2)
abline(v=d[3])
axis.Date(1,d,format=f)
axis.Date(3,at=d,format=f)
Barrowman, Nick <NBarrowman <at> cheo.on.ca> writes:
:
: I've run into a problem with the datetime axis generated by axis.POSIXct.
It appears a similar issue was
: discussed in October 2003 under the subject line "datetime data and
plotting" (see
: https://stat.ethz.ch/pipermail/r-help/2003-October/039071.html), but I
wasn't able to determine
: whether there is a straightforward solution.
:
: The code below produces a graph with apparently contradictory date labels on
the top and bottom axes:
:
: f <- "%Y/%m/%d"
: d <- as.POSIXct(strptime(c("2003/1/15","2003/1/16",
:
"2003/1/17","2003/1/18","2003/1/19"),format=f))
: plot(d,1:length(d),axes=F);box()
: axis(2)
: abline(v=d[3])
: axis.POSIXct(1,d,format=f)
: axis.POSIXct(3,at=d,format=f)
:
: On my copy of R (I have appended the version information below my
signature), this produces a graph with a
: vertical line that lines up with "2003/01/17" on the top axis, but
not on
the bottom axis.
:
: The issue seems to relate to time zones: here's what d looks like on my
computer:
:
: > d
: [1] "2003-01-15 Eastern Standard Time"
: [2] "2003-01-16 Eastern Standard Time"
: [3] "2003-01-17 Eastern Standard Time"
: [4] "2003-01-18 Eastern Standard Time"
: [5] "2003-01-19 Eastern Standard Time"
:
: (Actually I'm on Eastern Daylight Time, but let's ignore that for
now.)
:
: Changing the axes to display not only the date but also the time shows
what's going on:
:
: f <- "%Y/%m/%d"
: f2 <- "%Y-%m-%d %H:%M"
: d <- as.POSIXct(strptime(c("2003/1/15","2003/1/16",
:
"2003/1/17","2003/1/18","2003/1/19"),format=f))
: plot(d,1:length(d),axes=F);box()
: axis(2)
: abline(v=d[3])
: axis.POSIXct(1,d,format=f2)
: axis.POSIXct(3,at=d,format=f2)
:
: The bottom axis put the ticks at 19:00 on each date. This seems an odd time
until you note that Eastern
: Standard Time is 5 hours behind UTC, so 19:00 EST is 00:00 UTC.
:
: But is there any easy way to avoid this problem? It is confusing and
inconvenient that
: axis.POSIXct(1,d,format=f) and axis.POSIXct(3,at=d,format=f) give seemingly
contradictory scales.
:
: Many thanks for any help!
:
: Nick Barrowman, Ph.D.
: Chief Biostatistician, Chalmers Research Group
: Children's Hospital of Eastern Ontario Research Institute
: 401 Smyth Road, Ottawa, Ontario, K1H 8L1, Canada
: Tel (613) 737-7600 ext. 3971
: Fax (613) 738-4800
: Email nbarrowman <at> cheo.on.ca
: URL www.chalmersresearch.com
:
: > version
: _
: platform i386-pc-mingw32
: arch i386
: os mingw32
: system i386, mingw32
: status
: major 1
: minor 9.0
: year 2004
: month 04
: day 12
: language R
:
: ______________________________________________
: R-help <at> stat.math.ethz.ch mailing list
: https://www.stat.math.ethz.ch/mailman/listinfo/r-help
: PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
:
:
At 2:10 PM -0400 5/27/04, Barrowman, Nick wrote:>But is there any easy way to avoid this problem? It is confusing >and inconvenient that axis.POSIXct(1,d,format=f) and >axis.POSIXct(3,at=d,format=f) give seemingly contradictory scales.In one case you provide the locations of the tick marks, in the other case you let the function decide the locations. Why, in general, would anyone expect the two to be the same? (And that applies regardless of whether we're dealing with datetime values; the regular axis() function doesn't always give me tick marks at locations that I prefer.) Gabor Grothendieck's suggestion to use the Date class instead of POSIXt is a good one. -Don At 2:10 PM -0400 5/27/04, Barrowman, Nick wrote:>I've run into a problem with the datetime axis generated by >axis.POSIXct. It appears a similar issue was discussed in October >2003 under the subject line "datetime data and plotting" (see >https://stat.ethz.ch/pipermail/r-help/2003-October/039071.html), but >I wasn't able to determine whether there is a straightforward >solution. > >The code below produces a graph with apparently contradictory date >labels on the top and bottom axes: > >f <- "%Y/%m/%d" >d <- as.POSIXct(strptime(c("2003/1/15","2003/1/16", > "2003/1/17","2003/1/18","2003/1/19"),format=f)) >plot(d,1:length(d),axes=F);box() >axis(2) >abline(v=d[3]) >axis.POSIXct(1,d,format=f) >axis.POSIXct(3,at=d,format=f) > >On my copy of R (I have appended the version information below my >signature), this produces a graph with a vertical line that lines up >with "2003/01/17" on the top axis, but not on the bottom axis. > >The issue seems to relate to time zones: here's what d looks like on >my computer: > >> d >[1] "2003-01-15 Eastern Standard Time" >[2] "2003-01-16 Eastern Standard Time" >[3] "2003-01-17 Eastern Standard Time" >[4] "2003-01-18 Eastern Standard Time" >[5] "2003-01-19 Eastern Standard Time" > >(Actually I'm on Eastern Daylight Time, but let's ignore that for now.) > >Changing the axes to display not only the date but also the time >shows what's going on: > >f <- "%Y/%m/%d" >f2 <- "%Y-%m-%d %H:%M" >d <- as.POSIXct(strptime(c("2003/1/15","2003/1/16", > "2003/1/17","2003/1/18","2003/1/19"),format=f)) >plot(d,1:length(d),axes=F);box() >axis(2) >abline(v=d[3]) >axis.POSIXct(1,d,format=f2) >axis.POSIXct(3,at=d,format=f2) > >The bottom axis put the ticks at 19:00 on each date. This seems an >odd time until you note that Eastern Standard Time is 5 hours behind >UTC, so 19:00 EST is 00:00 UTC. > >But is there any easy way to avoid this problem? It is confusing >and inconvenient that axis.POSIXct(1,d,format=f) and >axis.POSIXct(3,at=d,format=f) give seemingly contradictory scales. > >Many thanks for any help! > >Nick Barrowman, Ph.D. >Chief Biostatistician, Chalmers Research Group >Children's Hospital of Eastern Ontario Research Institute >401 Smyth Road, Ottawa, Ontario, K1H 8L1, Canada >Tel (613) 737-7600 ext. 3971 >Fax (613) 738-4800 >Email nbarrowman at cheo.on.ca >URL www.chalmersresearch.com > > >> version > _ >platform i386-pc-mingw32 >arch i386 >os mingw32 >system i386, mingw32 >status >major 1 >minor 9.0 >year 2004 >month 04 >day 12 >language R > >______________________________________________ >R-help at stat.math.ethz.ch mailing list >https://www.stat.math.ethz.ch/mailman/listinfo/r-help >PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html-- -------------------------------------- Don MacQueen Environmental Protection Department Lawrence Livermore National Laboratory Livermore, CA, USA