ggplot2 2.2.1与R 3.5.0中scale_x_chron是否失效？

Hey there, let's tackle that frustrating error you're hitting when running the scale_x_chron example. I've seen this exact issue crop up with mismatched versions of ggplot2 and chron, especially on older R releases like 3.5.0. Here's what's going on and how to fix it:

What's Causing the Error? #

Your setup pairs ggplot2 2.2.1 (a pretty outdated version) with chron_2.3-45. The scale_x_chron function relies on how ggplot2 handles date/time objects, and the newer chron version expects a more modern POSIXct conversion workflow that your old ggplot2 doesn't support. That's why you're getting the "do not know how to convert 'x' to class POSIXct" message.

Three Practical Solutions #

1. Downgrade Chron to a Compatible Version #

Since updating ggplot2 on R 3.5.0 is tricky (newer ggplot2 versions require R 3.6+), rolling back chron to a version that plays nice with ggplot2 2.2.1 is a quick fix. Install chron_2.3-44 using this command:

install.packages("https://cran.r-project.org/src/contrib/Archive/chron/chron_2.3-44.tar.gz", repos = NULL, type = "source")

Don't forget to restart your R session after installing—this ensures the old version loads instead of the new one.

2. Bypass scale_x_chron by Converting to POSIXct #

If you don't want to mess with package versions, convert your chron dates to POSIXct manually and use ggplot2's native date scale instead. Here's how to adjust your code:

if(require("ggplot2")) { 
  dd <- data.frame(tt = chron(1:10), value = 101:110)
  # Convert chron object to POSIXct
  dd$tt_posix <- as.POSIXct(dd$tt)
  p <- ggplot(dd, aes(tt_posix, value)) + 
    geom_point() + 
    # Use ggplot2's built-in date scale with your desired format
    scale_x_datetime(date_labels = "%m-%d")
  print(p)
}

This uses ggplot2's native scale_x_datetime, which is more stable in older versions and avoids the compatibility gap.

3. Upgrade R and ggplot2 (Best Long-Term Fix) #

While this takes a bit more work, upgrading to a newer R version (4.0 or later) and the latest compatible ggplot2 will eliminate this and other potential compatibility headaches. Once you upgrade R, reinstall ggplot2 and chron to get their latest stable releases—this ensures all functions work as intended.

Verify the Fix #

After trying any of these solutions, re-run your code (or the modified version for option 2) to confirm the error is gone and your plot shows up with the correct date formatting.

内容的提问来源于stack exchange，提问作者Javi_VM