Changing the radius of a coord_polar ggplot

问题:

I'm looking to reduce the display radius of a pie chart built in ggplot2 relative to the rest of the plot (as the defaults keep cutting off my category labels).

Here's some dummy data and code that should show you what I'm experiencing:

library(ggplot2)
library(scales)
library(grid)

Region <- c("North America", "Central America", "South America", "Carribbean",
            "Western Africa", "Northern Africa", "Southern Afica", "Eastern Africa")
Conti <- c(rep("Americas",4), rep("Africa",4))
Freq <- c(runif(8, 1, 100))
Pct <- c(Freq/sum(Freq))
Pos <- c(cumsum(360*Pct)-(360*Pct/2))
Pos <- c(ifelse(Pos<=180,Pos,Pos-180))
df <- data.frame(Region, Conti, Freq, Pct, Pos)

pl <- ggplot(df, aes(x="", y=Freq, fill=Conti)) +
  geom_bar(stat="identity", color="black", width=1) +
  coord_polar(theta='y') +
  guides(fill=guide_legend(override.aes=list(colour=NA))) +
  theme(axis.line = element_blank(),
        axis.ticks=element_blank(),
        axis.title=element_blank(),
        axis.text.y=element_blank(),
        axis.text.x=element_text(color='black', size=18, angle=90-df$Pos),
        panel.background = element_blank(),
        panel.border = element_blank(),
        panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(),
        panel.margin = unit(0, "lines"),
        plot.background = element_rect(fill = "white"),
        plot.margin = unit(c(0, 0, 0, 0), "cm"),
        legend.position = "none") +
  scale_y_continuous(
    breaks=cumsum(df$Freq) - df$Freq/2,
    labels=paste0(df$Region," ",percent(df$Pct)))

print(pl)

If I reduce the size of the labels they become illegible relative to the pie and if I increase them they get cut-off. No matter how I try to adjust the aes(), limits, panel.margin etc. to get the balance right ggplot2 keeps automatically re-sizing the pie to occupy the same radii.

Ideally, I'd like to shrink the pie by half to allow more room for labels.

I appreciate that this isn't the prettiest plot, however, I'm updating an old figure so need to maintain the format for comparison. Any suggestions would be appreciated.

回答1:

My suggestion would be to use line breaks.

pl <- pl + scale_y_continuous(
  breaks=cumsum(df$Freq) - df$Freq/2,
  labels=paste0(sapply(strsplit(as.character(df$Region), " "), paste, collapse='\n'),
                "\n(", percent(df$Pct), ")"))
ggsave('pie.png', plot=pl, height=15, width=15)

回答2:

Some months later I've found that the answer lies in using a numeric dummy value for X (rather than a null value "") and then adding limits that are larger than x to the dummy x-axis. Code as below.

The issue then becomes adjusting the axis labels in to align with the new radius as hjust= and vjust= don't seem to work with coord_polar().

To do this I've added the labels as geom_text() and removed the automatic labels. This now does what I need.

The key changes are in the top and bottom lines.

pl <- ggplot(df, aes(x=0.8, y=Freq, fill=Conti)) +
  geom_bar(stat="identity", color="black", width=1) +
  coord_polar(theta='y') +
  geom_text(aes(x=1.65, y=cumsum(df$Freq) - df$Freq/2,
            label=paste0(df$Region," ",percent(df$Pct)),
            angle=90-df$Pos)) +
  guides(fill=guide_legend(override.aes=list(colour=NA))) +
  theme(axis.line = element_blank(),
        axis.ticks=element_blank(),
        axis.title=element_blank(),
        axis.text.y=element_blank(),
        axis.text.x=element_blank(),
        panel.background = element_blank(),
        panel.border = element_blank(),
        panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(),
        plot.background = element_rect(fill = "white"),
        plot.margin = unit(c(0, 0, 0, 0), "cm"),
        legend.position = "none") +
  scale_x_discrete(limits=c(0, 1))

print(pl)