将POSIXct传递给xlim

Question

Would some kind soul please explain why xlim does not acknowledge a POSIXct object as such in the following snippet:

y <- rnorm(3)
x <- c("2012-01-01", "2013-01-01", "2014-01-01")
x <- as.POSIXct(x) 
plot(y, xlim=range(x))

This results in an empty plot whose xlims are not dates but numeric equivalents and the following error:

Error in plot.window(...) : invalid 'xlim' value

I scoured old posts and some version of the following allegedly works

plot(y, xlim=seq(as.POSIXct("2012-01-01"), as.POSIXct("2014-01-01"), by="month")

But I received the same error when I tried. I'd settle for any way to denominate my xtick labels in dates, preferably months.

The snippet above is obviously trivialized to demonstrate my problem but I have verified that my actual x variable is a POSIXct object with dates of the form YYYY-MM-DD and my y is a vector of equal length to x.

Answer 1

You may try

 plot(x,y, xaxt='n')
 axis.POSIXct(side=1, x, format='%Y-%m-%d')

Other option is

 library(xts)
 x1 <- xts(y, order.by=x)
 plot(x1, xlim=range(index(x1)), type='p')