I have some difficulties in developing correct labeller function for adding x axis title within a facet_wrap plots. This is the code:

 str(R_macro_rev)
 tibble [857 ×ばつ 15] (S3: tbl_df/tbl/data.frame)
 $ OP_Age : chr [1:857] "<6" "<6" "<6" "<6" ...
 $ Thick : chr [1:857] "<3" "<3" "<3" "<3" ...
 $ Season : chr [1:857] "Rainy" "Rainy" "Rainy" "Rainy" ...
 $ D_Canal: num [1:857] 10 10 10 10 10 10 10 10 10 10 ...
 $ D_OPT : num [1:857] 1 1 1 2 2 2 3 3 3 4 ...
 $ Depth : num [1:857] 20 40 70 20 40 70 20 40 70 20 ...
 $ N : num [1:857] NA 15946 11816 13862 14955 ...
 $ P : num [1:857] 2082 1361 1931 1303 1641 ...
 $ K : num [1:857] 787 237 624 252 259 ...
 $ Ca : num [1:857] 1506 654 567 649 499 ...
 $ Mg : num [1:857] 282.3 32.7 566.7 89.7 99.8 ...
 $ NP : num [1:857] 10.35 11.71 6.12 10.64 9.11 ...
 $ NK : num [1:857] 27.4 67.3 18.9 54.9 57.8 ...
 $ PK : num [1:857] 2.65 5.75 3.09 5.17 6.35 ...
 $ CaMg : num [1:857] 5.33 NA 1 7.24 5
# look after the histogram
# firstly, cast the wrapper function to automatize the process
windowsFonts(Palatino=windowsFont("Palatino Linotype"))
plot_histograms <- function(data, columns = where(is.numeric), rename_vars = NULL) { 
 # Select columns properly
 selected_cols <- if (is.numeric(columns)) {
 names(data)[columns] # Select by index
 } else {
 names(select(data, {{ columns }})) # Select by condition (e.g., numeric)
 } 
 # Convert data to long format
 data_long <- data %>%
 pivot_longer(cols = all_of(selected_cols), names_to = "Variable", values_to = "Value") 
 # Rename variables if rename_vars is provided
 if (!is.null(rename_vars)) {
 data_long$Variable <- factor(data_long$Variable, 
 levels = selected_cols, 
 labels = ifelse(selected_cols %in% names(rename_vars), 
 rename_vars[selected_cols], 
 selected_cols))
 } else {
 data_long$Variable <- factor(data_long$Variable, levels = selected_cols)
 }
 # Plot histograms
 ggplot(data_long, aes(x = Value)) +
 geom_histogram(aes(y = after_stat(count)), bins = 30, fill = "#69b3a2", color = "#e9ecef", alpha = 0.9, na.rm = TRUE) +
 facet_wrap(~Variable, scales = "free") +
 theme_bw()+
 theme(text = element_text(family = "Palatino"))+
 labs(x = "Value", y = "Frequency")
}
plot_hist_all <- plot_histograms(data = R_macro_rev, 
 columns = 7:15, 
 rename_vars = c("N" = "Total N", "P" = "Total P", "K" = "Total K", "Ca" = "Total Ca", 
 "Mg" = "Total Mg","NP" = "N:P", "NK" = "N:K", "PK" = "P:K", "CaMg" = "Ca:Mg"))

And the resulting plot:

histogram1

Any new development in ggplot facet_wrap to add separate x axis title for each facet plot? so I can pass some labeller arguments in the wrapper function like this:

plot_hist_all <- plot_histograms(data = R_macro_rev, 
 columns = 7:15, 
 rename_vars = c("N" = "Total N", "P" = "Total P", "K" = "Total K", "Ca" = "Total Ca", 
 "Mg" = "Total Mg","NP" = "N:P", "NK" = "N:K", "PK" = "P:K", "CaMg" = "Ca:Mg"), # rename the stoichiometric vars
 rename_xlab = c("N" = "Total N (mg/kg)", "P" = "Total P (mg/kg)", "K" = "Total K (mg/kg)", "Ca" = "Total Ca (cmol(+)/kg)", 
 "Mg" = "Total Mg (cmol(+)/kg)", "NP" = "N:P", "NK" = "N:K", "PK" = "P:K", "CaMg" = "Ca:Mg"))
plot_hist_all

I've used annotate approach but, it must be set manually, and cannot automatically fit at the correct x axis location, like this:

hist2