Reverse datetime (POSIXct data) axis in ggplot

Question

I'm trying to create a plot of POSIXct times using ggplot, and would like to reverse the axis, but am struggling to make it work. I've been using scale_y_datetime, because in my real application, it's important that I have control of the breaks on this axis.

Here's an example of my problem, first with normal ordering, and then my attempt to reverse the axis.

# Some random dates and values to plot
MyData <-
  structure(list(Date = structure(c(1492979809.99827, 1492602845.68722, 
  1493093428.90318, 1492605578.0691, 1492961342.65056, 1492771976.83545, 
  1493020588.88485, 1493057018.85104, 1492852011.23873, 1492855996.55059
  ), class = c("POSIXct", "POSIXt")), Value = c(4.52885504579172, 
  6.0024610790424, 8.96430060034618, 7.06435370026156, 5.08460514713079, 
  3.47828012891114, 6.29844291834161, 0.898315710946918, 1.44857675535604, 
  5.74641009094194)), .Names = c("Date", "Value"), row.names = c(NA, 
  -10L), class = "data.frame")

library(ggplot2)
library(scales)
ggplot(MyData, aes(x=Value, y=Date)) +
  geom_point() + 
  scale_y_datetime(limits=c(min(MyData$Date),max(MyData$Date)))

which produces this:

If I attempt to reverse the Y axis, by reversing limits, I lose all breaks and data, like this:

ggplot(MyData, aes(x=Value, y=Date)) +
  geom_point() +
  scale_y_datetime(limits=c(max(MyData$Date),min(MyData$Date)))

Is there a simple way to reverse the datetime axis?

I'd question whether this is an appropriate visualization. Dates are usually independent variables and so (1) most people would expect to see them on the x-axis and (2) in that case, reversal would not make sense. Perhaps you could reverse by converting to "time since most recent date", _e.g._ `max(Date) - Date` ? — neilfws, Apr 26 '17 at 05:37
@neilfws I don't disagree with you. My example was just to illustrate the problem that I was having, and isn't exactly what I'm trying to achieve. My ultimate goal is to generate something which is more of a calendar style output, where I have Weeks on the Y axis, and days along the X axis. As when looking at a calendar, it makes more sense to show weeks progressing from top-to-bottom. Thanks! — David, Apr 26 '17 at 18:20
In that case I'd do a search for "ggplot2 calendar", sure to be a problem that others have thought about and addressed. — neilfws, Apr 26 '17 at 21:30

score 24 · Accepted Answer · edited Nov 14 '22 at 15:18

24

With the help from this post from Hadley Wickham here is how you can get a reverse datetime scale:

library(scales)
c_trans <- function(a, b, breaks = b$breaks, format = b$format) {
  a <- as.trans(a)
  b <- as.trans(b)
  
  name <- paste(a$name, b$name, sep = "-")
  
  trans <- function(x) a$trans(b$trans(x))
  inv <- function(x) b$inverse(a$inverse(x))
  
  trans_new(name, trans, inverse = inv, breaks = breaks, format=format)

}

rev_date <- c_trans("reverse", "time")

ggplot(MyData, aes(x=Value, y=Date)) +
  geom_point() + 
  scale_y_continuous(trans = rev_date)

Here is the plot:

edited Nov 14 '22 at 15:18

Oliver

8,169
3
15
37

answered Apr 26 '17 at 06:00

Marcelo

4,234
1
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18

Thanks for the link and the answer. This is working perfectly! – David Apr 26 '17 at 18:42
2

@Marcelo seems like this method no longer works as of ggplot2 version 3.0.0. Looks like the `trans_new()` arguments are in the wrong order and `format` gets passed as `minor_breaks`; explicitly naming the argument should fix it. – Mikko Marttila Jul 18 '18 at 10:45
I get: `Error in as.trans(a) : could not find function "as.trans"` – profPlum Jan 07 '21 at 01:02
1

@profPlum "as.trans" comes from the scales package. – David Jan 07 '21 at 22:51
you have to load the scales package – fc9.30 Jan 19 '21 at 13:48

score 3 · Answer 2 · answered Nov 14 '22 at 18:08

The accepted answer doesn't work for me anymore (R version 4.2.1). An option to fix this is by slightly modifying the function coord_x_datetime from the tidyquant package to reverse the datetime for your y-axis. Here is the function called coord_y_datetime:

coord_y_datetime <- function(xlim = NULL, ylim = NULL, expand = TRUE) {
  if (!is.null(ylim)) {
    ylim <- lubridate::as_datetime(ylim)
  }
  ggplot2::coord_cartesian(xlim = xlim, ylim = ylim, expand = expand)
}

Here is a reproducible example:

library(ggplot2)
ggplot(MyData, aes(x = Value, y = Date)) +
  geom_point() + 
  coord_y_datetime(ylim = c(max(MyData$Date), min(MyData$Date)))

^{Created on 2022-11-14 with reprex v2.0.2}

As you can see the y-axis datetime is now reversed.

Reverse datetime (POSIXct data) axis in ggplot

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