Ggplot, Facet, Piechart: Placing Text in the Middle of Pie Chart Slices

ggplot, facet, piechart: placing text in the middle of pie chart slices

NEW ANSWER: With the introduction of ggplot2 v2.2.0, position_stack() can be used to position the labels without the need to calculate a position variable first. The following code will give you the same result as the old answer:

ggplot(data = dat, aes(x = "", y = Cnt, fill = Volume)) + 
  geom_bar(stat = "identity") +
  geom_text(aes(label = Cnt), position = position_stack(vjust = 0.5)) +
  coord_polar(theta = "y") +
  facet_grid(Channel ~ ., scales = "free")

To remove "hollow" center, adapt the code to:

ggplot(data = dat, aes(x = 0, y = Cnt, fill = Volume)) + 
  geom_bar(stat = "identity") +
  geom_text(aes(label = Cnt), position = position_stack(vjust = 0.5)) +
  scale_x_continuous(expand = c(0,0)) +
  coord_polar(theta = "y") +
  facet_grid(Channel ~ ., scales = "free")

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OLD ANSWER: The solution to this problem is creating a position variable, which can be done quite easily with base R or with the data.table, plyr or dplyr packages:

Step 1: Creating the position variable for each Channel

# with base R
dat$pos <- with(dat, ave(Cnt, Channel, FUN = function(x) cumsum(x) - 0.5*x))

# with the data.table package
library(data.table)
setDT(dat)
dat <- dat[, pos:=cumsum(Cnt)-0.5*Cnt, by="Channel"]

# with the plyr package
library(plyr)
dat <- ddply(dat, .(Channel), transform, pos=cumsum(Cnt)-0.5*Cnt)

# with the dplyr package
library(dplyr)
dat <- dat %>% group_by(Channel) %>% mutate(pos=cumsum(Cnt)-0.5*Cnt)

Step 2: Creating the facetted plot

library(ggplot2)
ggplot(data = dat) + 
  geom_bar(aes(x = "", y = Cnt, fill = Volume), stat = "identity") +
  geom_text(aes(x = "", y = pos, label = Cnt)) +
  coord_polar(theta = "y") +
  facet_grid(Channel ~ ., scales = "free") 

The result:

R - pie chart in facet

Something like will work. You just have to change how your data is formatted and use ggplot2 which is in the tidyverse.

library(tidyverse)

df1 <- expand_grid(pie = 1:4, labels = c("monthly", "daily", "weekly"))
df2 <- tibble(slices = c(39, 7, 13,
                         40, 5, 12,
                         15, 27, 47,
                         58, 47, 2))

# join the data
df <- bind_cols(df1, df2) %>% 
  group_by(pie) %>% 
  mutate(pct = slices/sum(slices)*100) # pct for the pie - adds to 100
  
# graph
ggplot(df, aes(x="", y=pct, fill=labels)) + # pct used here so slices add to 100
  geom_bar(stat="identity", width=1) +
  coord_polar("y", start=0) +
  geom_text(aes(label = slices), position = position_stack(vjust=0.5)) +
  facet_wrap(~pie, ncol = 2) +
  theme_void() +
  theme(legend.position = "bottom")

Using an edited version of your data

> df
# A tibble: 12 x 4
# Groups:   pie [4]
     pie labels  slices   pct
   <int> <chr>    <dbl> <dbl>
 1     1 monthly     39    66
 2     1 daily        7    12
 3     1 weekly      13    22
 4     2 monthly     40    70
 5     2 daily        5     9
 6     2 weekly      12    21
 7     3 monthly     15    17
 8     3 daily       27    30
 9     3 weekly      47    53
10     4 monthly     58    54
11     4 daily       47    44
12     4 weekly       2     2

R + ggplot2 = add labels on facet pie chart

I would approach this by defining another variable (which I call pos) in df that calculates the position of text labels. I do this with dplyr but you could also use other methods of course.

library(dplyr)
library(ggplot2)

df <- df %>% group_by(year) %>% mutate(pos = cumsum(quantity)- quantity/2)

ggplot(data=df, aes(x=factor(1), y=quantity, fill=factor(prod))) +
  geom_bar(stat="identity") +
  geom_text(aes(x= factor(1), y=pos, label = quantity), size=10) +  # note y = pos
  facet_grid(facets = .~year, labeller = label_value) +
  coord_polar(theta = "y")

Pie plot getting its text on top of each other

here is an example:

pie <- ggplot(values, aes(x = "", y = val, fill = Type)) + 
  geom_bar(width = 1) + 
  geom_text(aes(y = val/2 + c(0, cumsum(val)[-length(val)]), label = percent), size=10)
pie + coord_polar(theta = "y")

Perhaps this will help you understand how it work:

pie + coord_polar(theta = "y") + 
  geom_text(aes(y = seq(1, sum(values$val), length = 10), label = letters[1:10]))

Changing the order of the slices in a pie chart in R

Convert your group column to a factor and set the levels in your desired order:

df <- data.frame(
  value = c(38, 20, 17, 10),
  group = c("Agricultural intensification", "Deforestation", "Urbanization", "Wetland or river modification")
)

library(ggplot2)

df$group <- factor(df$group, levels = rev(c("Agricultural intensification", "Urbanization", 
                                        "Wetland or river modification", "Deforestation")))

ggplot(df, aes(x = "", y = value, fill = group)) +
  labs(x = "Taxon order", y = "Driver", title = "Driver per taxon order") +
  theme(plot.title = element_text(hjust = 0.5, size = 20, face = "bold")) +
  geom_col(color = "black") +
  coord_polar("y", start = 0) +
  geom_text(aes(label = paste0(value, "%")), position = position_stack(vjust = 0.5)) +
  labs(x = NULL, y = NULL, fill = NULL) +
  theme(axis.line = element_line(), panel.grid.major = element_blank(), panel.grid.minor = element_blank(), panel.border = element_blank(), panel.background = element_blank()) +
  theme_void() +
  scale_fill_viridis_d()

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