Error message when creating ggplot with recession bands - r

Question

I have a dataset which plots unemployment over time, and I want to add in bands highlighting when there is a recession.
The original dataframe is called quarterly data.
recession <- data.frame(date_start= as_date(c("1973-07-01", "1980-01-01", "1990-07-01","2008-04-01")),
date_end = as_date(c("1975-07-01","1981-04-01", "1991-07-01","2009-04-01")))
recession$date_start <- ymd (recession$date_start)
recession$date_end <- ymd (recession$date_end)
ggplot(quarterly_data, aes(x=date, y= Unemployment))+
geom_line()+
geom_rect(data = recession, inherit.aes=FALSE , aes(xmin = date_start, xmax = date_end, ymin = -0.1, ymax = 0.1),
fill = "red", alpha= 0.3)
However, when I run the ggplot, I get this error message:
Error: Invalid input: time_trans works with objects of class POSIXct only
Does anyone know how to fix this?

Answer 1

While you have supplied us with the data frame recession, you have not supplied us with the data frame quarterly_data, where you are getting the error. A few pointers here to try, but first, a bit of description of what to gauge is causing this issue.
First of all, time_trans appears to be from the scales package, but it's not clear why that needs to run based on the code above. Is there anything else that could be using the scales package here?
Now for the error message itself, it requires an object of class POSIXct only. This is different than objects of class Date, which are created from the lubridate package that you are using, as apparent from the use of as_date to create the recession data frame.
You can confirm this yourself by running class(recession$date_start), where you can see the output is a Date class object.
After the ymd() function, you are also getting an object of class Date. From the documentation, you should be able to coerce the class to be converted to POSIXct POSIXt via supplying a tz= (time zone) argument. You can see this with the following:
> class(ymd(recession$date_start))
[1] "Date"
> class(ymd(recession$date_start, tz='GMT'))
[1] "POSIXct" "POSIXt"
So, that might fix your problem. But, you still have some detective work to do, since we don't have your other data frame and we apparently are not seeing a function that is trying to call time_trans from the scales package. The other possibility here is that ggplot is calling this to adjust an axis based on a POSIXt object... but I don't see a scale_ call or coord_flip() that might cause this error. I would recommend the following sequence:
Try the "homerun" approach by running your ymd() functions again, but supplying tz="GMT" to force the output to be a POSIXct object. Not sure if this will be successful.
run the ggplot() line itself. Do you get the same error? If so, the error lies within the quarterly_data data frame, and not the recession data frame. If it works, then run the ggplot() line and add in the geom_line() object. If it still works, then your issue is with the geom_rect function, which likely means the recession data frame.
Check the class of date objects in quarterly_data. Are they Date class or POSIXct class? If Date, try to convert them to POSIXct (maybe just use as.POSIXct()).
Is there more code that belongs here from your plot call? If you have coord_flip() or any scale_x or other thematic elements that are added to your plot code, they can definitely be trying to adjust the time scale and result in that error.