[R] ylab in plot.POSIXct

[Uwe Ligges]

Ed Kademan wrote:
> 
> I am using R-1.7.0 and have some data which consist of one vector of
> numbers and a second corresponding vector of dates belonging to the
> POSIXct class.  I would like to plot the numbers against the dates.
> What is the best way to do this?
> 
> It almost works to just call `plot.'  However if I do this while using
> the `ylab' parameter I get a warning message:
> 
>   parameter "ylab" couldn't be set in high-level plot() function

In this case, you can ignore that warning message (it's a warning, not
an error).


> Here is a function that demonstrates the behavior.
> 
>   ylabProblem <- function() {
>     x <- ISOdate(2003, 4, 1:10)           # POSIXct vector
>     y <- rnorm(10)
>     plot(x, y, ylab = 'I am y')
>   }
> 
> It works to invoke the low-level plotting routines by hand as follows:
> 
>   ylabNoProblem <- function() {
>     x <- ISOdate(2003, 4, 1:10)           # POSIXct vector
>     y <- rnorm(10)
>     plot.default(x, y, xaxt = 'n', xlab = '', ylab = 'I am y')
>     axis.POSIXct(1, x)
>   }
> 
> But I don't like calling methods explicitly like this.


axis.POSIXct() is not a method, because axis() is not a generic function
(and hence not able to dispatch for POSIXct objects).
Calling axis.POSIXct() explicitly is a not a bad idea in this case.

Uwe Ligges