ggplot pie chart choose axes ticks

Question

I would like to know if it's possible to modify the ticks of x axis with a ggplot pie chart.

Here what I can do :

# Some colors
couleurs <- data.frame(
id=seq(1,17,1),
mix=c(c(rep(1,6),rep(2,7),rep(3,4))),
html=c("#A00020","#109618","#388EE4","#C484D1","#FFAA33","#CCCDD0","#004AC5","#F80094","#CB5023","#638995","#33CFCF","#95DC4E","#F7D633","#5C403C","#F72020","#00D96C","#FDE4C5")
)
couleurs$html <- factor(couleurs$html, levels = couleurs$html[order(couleurs$id, decreasing = FALSE)])

# Data
activite <- data.frame(label=c("B to B","B to C","B to B / B to C", "B to B"), cible=c(rep("Externe",3), "Interne"), nb=c(12,9,3,12))
activite$label <- factor(activite$label, levels = activite$label[order(activite$nb[activite$cible=="Externe"], decreasing = TRUE)])
library(plyr)
activite<-ddply(activite,.(cible),transform,pc=(nb/sum(nb))*100)
activite

# Pie chart
library(ggplot2)
ggplot(data = activite, aes(x = "", y = nb, fill = label )) +
geom_bar(stat = "identity", position = position_fill(), width = 1) +
coord_polar(theta= "y", start = 0, direction = -1) +
labs(fill="") +
scale_fill_manual(values=as.character(couleurs$html[1:nrow(activite)]), labels=paste(activite$label,"\t\t\t",sep="")) +
geom_text(aes(label = paste(pc,"%", sep=" ")), size=4, colour = "white", fontface = "bold", position = position_fill(vjust = 0.5)) +
theme(strip.text = element_text(size=20, face = "bold", ), strip.background = element_rect(fill="grey75")) +
theme(panel.background = element_rect(fill = "white")) +
theme(plot.background = element_rect(fill = "grey92")) +
theme(legend.position="bottom", legend.background = element_rect(fill="grey92")) +
theme(legend.key = element_blank()) +
theme(panel.grid.minor = element_blank(), panel.grid.major = element_line(colour = "grey75")) +
theme(axis.text.y = element_blank()) +
theme(axis.ticks.length = unit(0, "mm")) +
theme(axis.title.x = element_blank(),axis.title.y = element_blank()) +
theme(legend.box.spacing = unit(1, "mm")) +
facet_wrap(~ cible)

Here my result:

After several hours of serach, I didn't find a solution to create what I want. The exact same pie chart but with personalised ticks like that :

With these particular conditions : - do not change the direction of the data in the pie chart, I want it like exactly this - if possible (but if not possible, it's okay), I would like the ticks' labels not superposed with the axis.

If someone can help me, I would really appreciate.

Answer 1

Here's one solution:

ggplot(data = activite %>%
         group_by(cible) %>%
         arrange(desc(nb)) %>%
         mutate(axis.label = cumsum(nb),
                axis.position = cumsum(pc)/100) %>%
         mutate(axis.label = ifelse(pc == min(pc),
                                    paste(axis.label, "0", sep = "-"),
                                    axis.label)), 
       aes(x = 1, y = nb, fill = label )) +
  geom_segment(aes(x = 1, xend = 1.6, y = axis.position, yend = axis.position),
               colour = "grey75") +
  geom_vline(xintercept = 1.6, colour = "grey75") +
  geom_bar(stat = "identity", position = position_fill(reverse = T), width = 1) +
  coord_polar(theta= "y", start = 0, direction = 1) +
  labs(fill="") +
  scale_fill_manual(values=as.character(couleurs$html[1:nrow(activite)]), labels=paste(activite$label,"\t\t\t",sep="")) +
  geom_text(aes(label = paste(pc,"%", sep=" ")), size=4, colour = "white", 
            fontface = "bold", position = position_fill(vjust = 0.5, reverse = T)) +
  geom_text(aes(x = 1.7, label = axis.label), size = 3,
            position = position_fill(reverse = T)) +
  theme(strip.text = element_text(size=20, face = "bold", ), strip.background = element_rect(fill="grey75")) +
  theme(panel.background = element_rect(fill = "white")) +
  theme(plot.background = element_rect(fill = "grey92")) +
  theme(legend.position="bottom", legend.background = element_rect(fill="grey92")) +
  theme(legend.key = element_blank()) +
  theme(panel.grid = element_blank()) +
  theme(axis.text = element_blank()) +
  theme(axis.ticks = element_blank()) +
  theme(axis.title = element_blank()) +
  theme(legend.box.spacing = unit(1, "mm")) +
  facet_wrap(~ cible)

Explanation:

1. The sequence in your labels went clockwise, while the direction of the polar coordinates went counter-clockwise. That makes labelling rather troublesome. I switched the direction for polar coordinates, & added reverse = T inside the position adjustment calls for the geoms.

2. It's hard to assign different axis breaks to different facets of the same plot, so I didn't. Instead, I modified the data to include calculated axis labels / margin positions, added margins via geom_segment / geom_vline, & hid the axis text / ticks in theme().