How to center ggplot plot title

问题

The "lege artis" way to center justify a plot title in ggplot - plot.title = element_text(hjust = 0.5) - centers the title over plot area excluding axis labels.

This can get ugly when the axis labels are very long, such as this plot of songs in Mary Poppins Soundtrack vs. their character length.

library(tidyverse)

mary_poppins <- data_frame(song = c("Overture", "Sister Suffragette", "The Life I Lead", "The Perfect Nanny", "A Spoonful of Sugar", "Pavement Artist", "Jolly Holiday", "Supercalifragilisticexpialidocious", "Stay Awake", "I Love to Laugh", "A British Bank", "Feed the Birds ", "Fidelity Fiduciary Bank", "Chim Chim Cher-ee", "Step in Time", "A Man Has Dreams", "Let's Go Fly a Kite"
))

mary_poppins <- mary_poppins %>%
  mutate(len = nchar(song))

ggplot(data = mary_poppins, aes(x = reorder(song, len), y = len)) +
  geom_col(fill = "firebrick") +
  coord_flip() +
  theme_light() +
  theme(axis.title.y = element_blank(),
        axis.text = element_text(size = rel(1.5)),
        plot.title = element_text(size = rel(2.5), face = "bold", hjust = 0.5, 
                                  margin = margin(t = 10, b = 20, unit = "pt"))) +
  ggtitle("Mary Poppins") +
  ylab("Lenght of title (characters)")

Is there a way to center the title over the total plot area, i.e . including the area taken over by axis labels?

回答1:

Alternately, you can use gridExtra::grid.arrange and grid::textGrob to create the title without needing to pad it visually. This basically creates a separate plot object with your title and glues it on top, independing of the contents of your ggplot call.

First store your whole ggplot call in a variable, e.g. p1:

grid.arrange(textGrob("Mary Poppins", 
               gp = gpar(fontsize = 2.5*11, fontface = "bold")), 
             p1, 
             heights = c(0.1, 1))

You have to translate your theme() settings to gpar(). The base size of theme_light is 11, which is where the 2.5*11 comes from (and the 2.5 from your rel(2.5)).

The advantage here is that you know your title will be truly centered, not just close enough by eye.

回答2:

Solution adding white space to centre title:

Add spaces after the title with:

ggtitle(paste0("Mary Poppins", paste0(rep("", 30), collapse = " ")))

For the output like this:

Not perfect solution, but works.

回答3:

Short solution I've found:

theme(plot.title = element_text(hjust = -0.2))

hjust parameter controls distance from the left alignment to the y axis. Negative values move text to the left

回答4:

If you're in a hurry, adding spaces after title in ggtitle will also work...

ggtitle("Mary Poppins                                 ") +

Output:

来源：https://stackoverflow.com/questions/46287086/how-to-center-ggplot-plot-title

标签

ggplot2

data-visualization