How to export high resolution ggplot graphic with unicode arrows

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I am struggling to export the following ggplot2 graphic (legend) with Unicode arrows. This is the Plot Zoom output.

Text

The code used to create this legend is the following:

legend <- ggplot() +
  geom_tile(
    data = bivariate_color_scale,
    mapping = aes(
      x = gini,
      y = mean,
      fill = fill)
  ) +
  scale_fill_identity() +
  labs(y ="Higher bus. density →",
       x = "Higher patent growth →", 
       title = "Legend") +
  theme_minimal()+
  theme(
    panel.grid.minor = element_blank(), 
    panel.grid.major = element_blank(), 
    axis.line = element_blank(),
    axis.ticks = element_blank(),
    panel.border = element_blank(),
    axis.text.x = element_blank(),
    axis.text.y = element_blank() 
    ) +
  # make font small enough
  theme(axis.title = element_text(size = 8)) +
  # quadratic tiles
  coord_fixed()

I have tried to export this legend (in high resolution) with the following two codes:

ggsave(filename="legend.png", 
       plot = legend,
       dpi= 300,
       width = 210, 
       height = 180, 
       units = "mm")

and ...

ggsave(filename="legend.pdf",
       plot = legend, 
       dpi = 300, 
       device = cairo_pdf,
       width = 210, 
       height = 180, 
       units = "mm"
       )

Both codes did not properly translate/save the Unicode arrows (see the following output).

enter image description here

Does anybody have a suggestion on how I can export this graphic in high resolution with Unicode arrows? thank you in advance.

Data

bivariate_color_scale <- data.frame(gini = rep(1:3, 3), mean = rep(1:3, each = 3),
                                    fill = c("#beafc4", "#ae667c", "#9c263c",
                                             "#778fbd", "#6d5577", "#63233b",
                                             "#3970b3", "#354374", "#301d39"))
cairo ggplot2 r
2 Answers

For display of Unicode characters you can use expression(), or (my preference) use sprintf(), then call the character inline with text using the preamble \u. See the following example:

df <- data.frame(x=1:10, y=1:10)

ggplot(df, aes(x,y)) + geom_point() +
  labs(
    title=paste("This Title has an up arrow!", sprintf('\u2191')),
    x=paste('The x axis goes this way:', sprintf('\u2794')),
    y=paste('The y axis is this way:',sprintf('\u2190'))
  )

enter image description here

user_96647960

The fundamental problem is that you need to use a font that actually contains the unicode symbol you want to show. You're not specifying a particular font, so the graphics device is free to choose, and both png() and pdf() choose Helvetica which doesn't have your symbol. The interactive device probably choses Arial (are you on Windows?), which does have the symbol.

# code setup
library(ggplot2)

bivariate_color_scale <- data.frame(gini = rep(1:3, 3), mean = rep(1:3, each = 3),
                                    fill = c("#beafc4", "#ae667c", "#9c263c",
                                             "#778fbd", "#6d5577", "#63233b",
                                             "#3970b3", "#354374", "#301d39"))

legend <- ggplot() +
  geom_tile(
    data = bivariate_color_scale,
    mapping = aes(
      x = gini,
      y = mean,
      fill = fill)
  ) +
  scale_fill_identity() +
  labs(y ="Higher bus. density →",
       x = "Higher patent growth →", 
       title = "Legend") +
  theme_minimal()+
  theme(
    panel.grid.minor = element_blank(), 
    panel.grid.major = element_blank(), 
    axis.line = element_blank(),
    axis.ticks = element_blank(),
    panel.border = element_blank(),
    axis.text.x = element_blank(),
    axis.text.y = element_blank() 
  ) +
  # quadratic tiles
  coord_fixed()

# with Helvetica the symbol doesn't show
legend +
  theme(axis.title = element_text(family = "Helvetica"))


# with Arial the symbol shows
legend +
  theme(axis.title = element_text(family = "Arial"))

Created on 2020-06-27 by the reprex package (v0.3.0)

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