R help - Apr 2006 - Tick mark alignment for POSIXct data

I am using POSIXct objects to store my date/time information.  If I am
plotting less that 2 days worth of data, I get the correct tick marks on the
x-axis which is showing the 'day HH:MM' and these line up with the data
points.

If the data spans more than 2 days, the tick marks are now off.  In the data
below, I am creating some sample data and plotting the points.  I am in the
Eastern Timezone.  When the second plot is generated, the tick marks are 4
hours behind the actual time; it appears that the data is being plotted in
GMT, but the tick marks are EDT.  I as looking in axis.POSIXct and it
appears that the rounding that is done for 'pretty printing' the x-axis
is
normalized to GMT, so that the tick marks are plotted 4 hours before the
data points.

Is there a way of carrying the time zone into axis.POSIXct so that the ticks
marks are generated in the correct locations?

###=========test script   ---   Eastern Time Zone==========# generate less than
2 days of data points
x.1 <- seq(as.POSIXct('2006-6-1 00:00:00'), as.POSIXct('2006-6-2
12:00:00'),
by='2 hours')
plot(x.1, seq(length(x.1)), main='tick marks aligned') # default

# now setup 4 days worth of data; tick marks don't line up as expected
x.1 <- seq(as.POSIXct('2006-6-1 00:00:00'), as.POSIXct('2006-6-5
00:00:00'),
by='day')
plot(x.1, seq(length(x.1)), main='tick marks not aligned') # default




--
Jim Holtman
Cincinnati, OH
+1 513 646 9390 (Cell)
+1 513 247 0281 (Home)

What the problem you are trying to solve?

	[[alternative HTML version deleted]]

Read the R News 4/1 help desk article which specifically discusses this.

On 4/17/06, jim holtman <jholtman at gmail.com>
wrote:
> I am using POSIXct objects to store my date/time information.  If I am
> plotting less that 2 days worth of data, I get the correct tick marks on
the
> x-axis which is showing the 'day HH:MM' and these line up with the
data
> points.
>
> If the data spans more than 2 days, the tick marks are now off.  In the
data
> below, I am creating some sample data and plotting the points.  I am in the
> Eastern Timezone.  When the second plot is generated, the tick marks are 4
> hours behind the actual time; it appears that the data is being plotted in
> GMT, but the tick marks are EDT.  I as looking in axis.POSIXct and it
> appears that the rounding that is done for 'pretty printing' the
x-axis is
> normalized to GMT, so that the tick marks are plotted 4 hours before the
> data points.
>
> Is there a way of carrying the time zone into axis.POSIXct so that the
ticks
> marks are generated in the correct locations?
>
> ###=========test script   ---   Eastern Time Zone==========> # generate
less than 2 days of data points
> x.1 <- seq(as.POSIXct('2006-6-1 00:00:00'),
as.POSIXct('2006-6-2 12:00:00'),
> by='2 hours')
> plot(x.1, seq(length(x.1)), main='tick marks aligned') # default
>
> # now setup 4 days worth of data; tick marks don't line up as expected
> x.1 <- seq(as.POSIXct('2006-6-1 00:00:00'),
as.POSIXct('2006-6-5 00:00:00'),
> by='day')
> plot(x.1, seq(length(x.1)), main='tick marks not aligned') #
default
>
>
>
>
> --
> Jim Holtman
> Cincinnati, OH
> +1 513 646 9390 (Cell)
> +1 513 247 0281 (Home)
>
> What the problem you are trying to solve?
>
>        [[alternative HTML version deleted]]
>
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