x axis as week number and secondary x-axis as date

Question

I'm trying to plot a time serie with Primary x-axis as numeric and Secondary x-axis as date in ggplot. This is my poor try.

library(tidyverse)

tibble::tribble(
  ~date,  ~ndvi,
  "2020-05-18", 0.7655,
  "2020-06-14",  0.723,
  "2020-07-12", 0.6178,
  "2020-08-21",  0.437,
  "2020-09-07", 0.4763,
  "2020-09-10", 0.4928,
  "2020-09-12", 0.4831,
  "2020-09-22", 0.4774,
  "2020-10-02", 0.5794,
  "2020-10-07",  0.606
) %>% 
  mutate(date = lubridate::ymd(date),  
         weeks = difftime(date, min(date), units="weeks")) %>% 
  ggplot(aes(weeks, ndvi)) +
  geom_line()+
  scale_x_datetime(
    sec.axis = dup_axis(name = "", #breaks = date, 
                        labels = scales::time_format("%b")))

#> Error: Invalid input: time_trans works with objects of class POSIXct only

And this is the desired output, where the Primary x-axis has weeks and Secondary x-axis has the months of the time serie

You haven't described your desired output. The image you included looks like the current output produced from your code. Can you be specific about what you wish to change? — Z.Lin, Feb 10 '21 at 01:33
`scales::time_format("%^b")` seems a typo. `labels = scales::time_format("%b")` works as expected — Ronak Shah, Feb 10 '21 at 02:33
Thanks @RonakShah but I don't think that is the problem with my code — Juanchi, Feb 10 '21 at 09:37

score 2 · Answer 1 · answered Feb 10 '21 at 10:13

set labels for both x-axes separately. Please check also this discussion

library(tidyverse)

mydat <- tibble::tribble(
  ~date,  ~ndvi,
  "2020-05-18", 0.7655,
  "2020-06-14",  0.723,
  "2020-07-12", 0.6178,
  "2020-08-21",  0.437,
  "2020-09-07", 0.4763,
  "2020-09-10", 0.4928,
  "2020-09-12", 0.4831,
  "2020-09-22", 0.4774,
  "2020-10-02", 0.5794,
  "2020-10-07",  0.606
)  %>% 
  mutate(date = lubridate::ymd(date),  
         weeks = as.numeric(difftime(date, min(date), units="weeks")))

 mydat %>%
  ggplot(aes(date, ndvi)) +
  geom_line() +
  scale_x_date(date_breaks = "4 weeks", labels = scales::date_format("%W"),
    sec.axis = dup_axis(name = "", labels = scales::date_format("%b")))

^{Created on 2021-02-10 by the reprex package (v1.0.0)}

Thanks @tjebo, this is really helpful however I could probably was not very clear in my question since I would like to use new column `weeks` in x-axis — Juanchi, Feb 10 '21 at 12:14

x axis as week number and secondary x-axis as date

1 Answers1