Transforming 24 hour time into 12-hour format with %p to see AM/PM: issue with OS in R

Question

For a journal, I was requested to transform my 24-hour x-axis into a 12-hour format with AM/PM format. I am using R with ggplot2 package to create my plots. For this, I did use the %p option allowing to see AM/PM. When I used it, it did not work at all. After looking on internet and discussing with colleagues, I realized that %p was not working on my Linux machine, but was working on my Mac machine. Thus, I would highly appreciate any feedback why.

Here is a reprex:

library(tidyverse)
library(lubridate)
library(ggplot2)

df <- tibble::tibble(ID = sample(seq(1, 3, 1), 289, replace = T), 
                     time = seq(as.POSIXct("2017-01-01", tz = "UTC"),
                                as.POSIXct("2017-01-02", tz = "UTC"),
                                by = "5 min"), 
                     date = lubridate::as_date(time),
                     outcome = sample(seq(70, 120, 1), 289, replace = T))


ggplot(df, aes(x = time, 
               y = outcome, 
               group = ID)) +
  geom_line(aes(color = factor(ID))) + 
  scale_y_continuous(limits = c(0, 150)) +
  scale_x_datetime(date_labels = ("%I %p"),
                   timezone = "GMT", 
                   date_breaks = "4 hours",
                   expand = c(0, 0))

The output on the Mac machine is:

The output on the Linux machine is:

Finally, the sessionInfo() for both:

1. Mac:

sessionInfo(package = NULL) 
# R version 3.5.3 (2019-03-11) 
# Platform: x86_64-apple-darwin15.6.0 (64-bit) 
# Running under: macOS High Sierra 10.13.6 
# 
# Matrix products: default BLAS: /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib 
# LAPACK: /Library/Frameworks/R.framework/Versions/3.5/Resources/lib/libRlapack.dylib 
# 
# locale: 
# [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
#     
# attached base packages: 
# [1] stats     graphics  grDevices utils     datasets  methods   base      
#     
# other attached packages: 
# [1] ggplot2_3.2.1   lubridate_1.7.4 
#     
# loaded via a namespace (and not attached): 
#  [1] Rcpp_1.0.3       rstudioapi_0.10  magrittr_1.5     tidyselect_0.2.5 munsell_0.5.0    colorspace_1.4-1 R6_2.4.1         rlang_0.4.2      stringr_1.4.0    
# [10] dplyr_0.8.1      tools_3.5.3      grid_3.5.3       gtable_0.3.0     withr_2.1.2      digest_0.6.23    lazyeval_0.2.2   assertthat_0.2.1 tibble_2.1.3    
# [19] lifecycle_0.1.0  crayon_1.3.4     purrr_0.3.2      farver_2.0.1     glue_1.3.1       labeling_0.3     stringi_1.4.3    compiler_3.5.3   pillar_1.4.2    
# [28] scales_1.1.0     pkgconfig_2.0.3

2. Linux:

sessionInfo(package = NULL)
# R version 3.6.2 (2019-12-12)
# Platform: x86_64-pc-linux-gnu (64-bit)
# Running under: Ubuntu 18.04.4 LTS
# 
# Matrix products: default
# BLAS:   /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.7.1
# LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.7.1
# 
# Random number generation:
#  RNG:     Mersenne-Twister 
#  Normal:  Inversion 
#  Sample:  Rounding 
#  
# locale:
#  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=de_CH.UTF-8       
#  [4] LC_COLLATE=en_US.UTF-8     LC_MONETARY=de_CH.UTF-8    LC_MESSAGES=en_US.UTF-8   
#  [7] LC_PAPER=de_CH.UTF-8       LC_NAME=C                  LC_ADDRESS=C              
# [10] LC_TELEPHONE=C             LC_MEASUREMENT=de_CH.UTF-8 LC_IDENTIFICATION=C       
# 
# attached base packages:
# [1] stats     graphics  grDevices utils     datasets  methods   base     
# 
# other attached packages:
# [1] ggplot2_3.2.1   lubridate_1.7.4
# 
# loaded via a namespace (and not attached):
#  [1] Rcpp_1.0.3       rstudioapi_0.10  magrittr_1.5     tidyselect_0.2.5 munsell_0.5.0   
#  [6] colorspace_1.4-1 R6_2.4.1         rlang_0.4.4      stringr_1.4.0    dplyr_0.8.3     
# [11] tools_3.6.2      grid_3.6.2       gtable_0.3.0     withr_2.1.2      digest_0.6.23   
# [16] lazyeval_0.2.2   assertthat_0.2.1 tibble_2.1.3     lifecycle_0.1.0  crayon_1.3.4    
# [21] purrr_0.3.3      farver_2.0.2     glue_1.3.1       labeling_0.3     stringi_1.4.5   
# [26] compiler_3.6.2   pillar_1.4.3     scales_1.1.0     pkgconfig_2.0.3

Thank you in advance for any guidance!

Answer 1

Your problem appears to be the following setting: LC_TIME=de_CH.UTF-8 . I assume the swiss German time format does not know AM/PM (because German doesn't use that nonese but proper 24h times). I see that you have locales availbe that can deal with that though. So you have to set one of the others for time locale:

Sys.setlocale("LC_TIME", "en_US.UTF-8")  

Test with:

format.Date(df$time, "%I %p")

And then see if the rest of your code works now. You have to set the locale after every restart of R or make the switch permanent using your R profile .