Matplot does not work with x being POSIXt class (PR#9412)

As Peter said, matplot plots matrices. The columns of a matrix are 
vectors of numbers. A POSIXlt object is not a vector of numbers, it 
is a list. So it shouldn't work. And should not be expected to work.

But with a POSIXct object it will work.

x <- strptime(as.character(x), format="%Y-%m-%d")
## [1] "POSIXt"  "POSIXlt"
matplot( as.POSIXct(x), y)

Hi,

Matplot works with x being Date class but not POSIXt. Here is the
example with R version 2.5.0 Under development (unstable) (2006-12-06
r40129)

Example:

x <- Sys.Date() - c(1:10)
y <- cbind(1:10, 10:1)
class(x)
## [1] "Date"
matplot(x, y)

x <- strptime(as.character(x), format="%Y-%m-%d")
## [1] "POSIXt"  "POSIXlt"
matplot(x, y)
Error in matplot(x, y) : 'x' and 'y' must have only 1 or the same number
of columns

Additionally, matplot with x being Date class does not use apropriate
annotation for x axis.

This is very easy to obtain:

# x is a Date object
matplot(x,y,xaxt='n')
axis.Date(1,x)

or

# x is a POSIXlt object
matplot( as.POSIXct(x), y,xaxt='n')
axis.POSIXct(1,x)

So easy, in fact, that I personally would not expect R core to spend 
time on it. One of the virtues of R is that the language is so rich 
that little tweaks like this are often very easy.

Thank you!

Gregor

-Don

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Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA