How to add a text annotations to a time series ggplot

Question

I know about annotate() and that you need to add the x and y coordinates. The problem is my x is class ""POSIXct" "POSIXt." So when I try to use annotate, R responds, object needs to be POSIXct. I have tried various combinations trying to fix this ... no success. Any ideas?

Where's the code so others don't have to mock up an example for you? Also, why not just convert the `lt` to ` ct`? — hrbrmstr, Oct 16 '18 at 19:30

score 3 · Accepted Answer · answered Oct 16 '18 at 19:34

Make sure the x argument in annotate is coded as POSIXct. For example, using the barley dataset from the lattice package, we can recode the year to POSIXct and then annotate:

library(lattice)
library(tidyverse)

barley %>%
  #convert year from factor to numeric, and then to POSIXct
  mutate(year = as.numeric(levels(year))[year],
         year = as.POSIXct(paste0(year, "-01-01"))) %>% 
  group_by(year) %>% 
  summarise(AvgYield = mean(yield)) %>% 
  ggplot(aes(year, AvgYield)) + 
    geom_line() + 
    #now to annotate, just make sure to code x as POSIXct 
    #in a range that will appear on the plot
    annotate("text", x = as.POSIXct("1931-04-01"), y = 34, label = "Some text")

How to add a text annotations to a time series ggplot

1 Answers1