[Rd] matplot.Date & matplot.POSIXct

Spencer Graves @pencer@gr@ve@ @end|ng |rom prod@y@e@com
Tue Jan 28 06:02:28 CET 2020

       Thanks for the reply.

On 2020-01-27 19:56, Abby Spurdle wrote:
> Maybe I'm missing something really obvious here, but I was unable to
> create a matrix out of POSIXct object(s).
> Perhaps that deserves a separate discussion...?

       Can you provide an example?

       The standard matplot application that concerns me is with 
matplot(x, y, ...) where x has class Date or POSIXct and y is a matrix.  
The "fda" package on CRAN includes a "matplot" help page with examples 
that worked when I tested them recently.

       If you have an example that you think should work but doesn't I'd 
like to know.  Maybe it should be added to the examples in 
fda::matplot.Rd file, then the code should be modified until it works.
> Regarding your other comments/questions:
> (1) You should *NOT* mask functions from the graphics package (or
> base, stats, etc), except possibly for personal use.
> (2) The xlab and ylab are fine.

       In most situations, I agree with your comment that, "You should 
*NOT* mask functions from the graphics package (or base, stats, etc)".

       However, when the behavior of the function in graphics, base, or 
stats seems patently inappropriate and not adequately considered, then I 
think that someone should mask the function in the core distribution 
with one whose behavior seems more consistent with what most users would 
most likely want.

       Ten or twelve years ago, I concluded that the behavior of 
graphics::matplot(x, y, ...) was inappropriate when x is either of class 
Date or POSIXct.  Specifically, it labeled the horizontal axis the same 
as graphics::matplot(as.numeric(x), y, ...).  I think it should instead 
be labeled the same as graphics::plot(x, y[,1], ...) in such cases.  To 
fix this problem, I made fda::matplot generic; graphics::matplot is not 
generic.  And a coded methods for x of class numeric, matrix, Date and 
POSIXct plus a default.  Each calls either graphics::matplot or matlines 
as appropriate after first setting up the horizontal axis properly if x 
is of class Date or POSIXct.

       For specific examples, consider the following taken from 

invasion1 <- as.Date('1775-09-04')
invasion2 <- as.Date('1812-07-12')
earlyUS.Canada <- c(invasion1, invasion2)
Y <- matrix(1:4, 2, 2)
graphics::matplot(earlyUS.Canada, Y)
# horizontal axis labeled per as.numeric(earlyUS.Canada),
# NOT as Dates
fda::matplot(earlyUS.Canada, Y)
# problem fixed.

AmRev.ct <- as.POSIXct1970(c('1776-07-04', '1789-04-30'))
graphics::matplot(AmRev.ct, Y)
# horizontal axis labeled per as.numeric(AmRev.ct),
# NOT as POSIXct
fda::matplot(AmRev.ct, Y)
# problem fixed.

       Thanks again for the reply.
       Spencer Graves
> B.

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