How to center align a wrapped axis title in ggplot2?-CodePudding

I have a really long y-axis title with scientific notation that I want to wrap and make center aligned. I can either wrap the title and have it left aligned, or center an incorrect format of the title. How can I wrap the axis title AND have it centered in ggplot2?

Example Data

set.seed(321)
df <- data.frame(matrix(ncol = 2, nrow = 3))
colnames(df)[1:2] <- c("date","value")
df$value <- round(rnorm(3, 100,30),0)
st <- as.Date("2020-01-01")
en <- as.Date("2020-03-31")
df$date <- seq.Date(st,en,by = '1 month')

This makes the ggplot2 figure with the unwrapped long y-axis title

library(ggplot2)

ggplot(df, aes(x = date, y = value))  
  geom_point()  
  labs(x = "",
       y = expression(paste("Here is a really really really looooonnnng title with notation (  ", m^-2,")")))  
  scale_x_date(breaks = seq(st, en, by = "1 month"),
               limits = c(st,en),
               date_labels = "%b %Y")  
  scale_y_continuous(limits = c(0,150),
                     breaks=seq(0,150,25))  
  theme_bw()  
  theme(panel.grid = element_blank(),
        text = element_text(size = 16),
        axis.text.x = element_text(size = 14, color = "black", angle = 90, vjust = 0.5, hjust = 1),
        axis.text.y = element_text(size = 14, color = "black"))

I have tried using \n which wraps the title but, the title is not centered, it is left aligned

ggplot(df, aes(x = date, y = value))  
  geom_point()  
  labs(x = "",
       y = expression(paste("Here is a really really really \n looooonnnng title with notation (  ", m^-2,")")))  
  scale_x_date(breaks = seq(st, en, by = "1 month"),
               limits = c(st,en),
               date_labels = "%b %Y")  
  scale_y_continuous(limits = c(0,150),
                     breaks=seq(0,150,25))  
  theme_bw()  
  theme(panel.grid = element_blank(),
        text = element_text(size = 16),
        axis.text.x = element_text(size = 14, color = "black", angle = 90, vjust = 0.5, hjust = 1),
        axis.text.y = element_text(size = 14, color = "black"))

Using str_wrap() centers the title but the title is no longer formatted correctly

library(stringr)

ggplot(df, aes(x = date, y = value))  
  geom_point()  
  labs(x = "",
       y = str_wrap(
         expression(paste("Here is a really really really \n looooonnnng title with notation (  ", m^-2,")")),50)
       ) 
  scale_x_date(breaks = seq(st, en, by = "1 month"),
               limits = c(st,en),
               date_labels = "%b %Y")  
  scale_y_continuous(limits = c(0,150),
                     breaks=seq(0,150,25))  
  theme_bw()  
  theme(panel.grid = element_blank(),
        text = element_text(size = 16),
        axis.text.x = element_text(size = 14, color = "black", angle = 90, vjust = 0.5, hjust = 1),
        axis.text.y = element_text(size = 14, color = "black"))

I tried creating a wrapper function based on this similar SO question but it also did not format the title correctly

wrapper <- function(x, ...) 
{
  paste(strwrap(x, ...), collapse = "\n")
}

my_title = expression(paste("Here is a really really really looooonnnng title with notation (  ", m^-2,")"))

ggplot(df, aes(x = date, y = value))  
  geom_point()  
  labs(x = "",
       y = wrapper(my_title, 50))  
  scale_x_date(breaks = seq(st, en, by = "1 month"),
               limits = c(st,en),
               date_labels = "%b %Y")  
  scale_y_continuous(limits = c(0,150),
                     breaks=seq(0,150,25))  
  theme_bw()  
  theme(panel.grid = element_blank(),
        text = element_text(size = 16),
        axis.text.x = element_text(size = 14, color = "black", angle = 90, vjust = 0.5, hjust = 1),
        axis.text.y = element_text(size = 14, color = "black"))

CodePudding user response：

You can try to use the package ggtext. If we want to use it, we need to change the normal expression style to HTML and CSS style (which is <sup></sup> for superscript).

For clearer code, I've put your y-axis title into a variable y_lab. The code that is doing the job is theme(axis.title.y = element_textbox_simple(orientation = "left-rotated", halign = 0.5)).

library(ggplot2)
library(ggtext)

y_lab <- "Here is a really really really looooonnnng<br>title with notation (m<sup> -2</sup>)"
ggplot(df, aes(x = date, y = value))  
  geom_point()  
  labs(x = "",
       y = y_lab) 
  scale_x_date(breaks = seq(st, en, by = "1 month"),
               limits = c(st,en),
               date_labels = "%b %Y")  
  scale_y_continuous(limits = c(0,150),
                     breaks=seq(0,150,25))  
  theme_bw()  
  theme(panel.grid = element_blank(),
        text = element_text(size = 16),
        axis.text.x = element_text(size = 14, color = "black", angle = 90, vjust = 0.5, hjust = 1),
        axis.text.y = element_text(size = 14, color = "black"),
        axis.title.y = element_textbox_simple(orientation = "left-rotated", halign = 0.5))