Create Multiple Pie Charts using ggplot2 in R

Pie Chart, also known as circle chart, is the graphical representation of the relative size or frequency of the data in a circular format. Basically, it helps in visualizing the relative size or frequency of a particular group of data as a part of the whole. This article discusses how multiple pie charts can be created into one frame for consecutive comparison.

Function used:

• pie() function as the name suggests is used for visualizing a pie chart.

Syntax: pie(x, labels, radius, main, col, clockwise)

Parameters:

• x: This parameter is the vector containing the value of the pie chart.
• labels: This parameter is the vector containing the labels of all the slices in Pie Chart.
• radius: This parameter is the value of the radius of the pie chart. This value is between -1 to 1.
• main: This parameter is the title of the chart.
• col: This parameter is the color used in the pie chart.
• clockwise: This parameter is the logical value which is used to draw the slices in clockwise or anti-clockwise direction.

• coord_polar() function is used to create a polar coordinate system, which helps in drawing a pie chart.

Syntax:

coord_polar(theta = "x", start = 0, direction = 1, clip = "on")

Parameter:

• theta represents the angle
• start used for setting offset
• direction 
• clip decides whether drawing should be clipped or not

• facet_grid() creates a matrix to display rows and columns faceting variables

Syntax:

facet_grid(facets, margins=FALSE, scales="fixed", space="fixed", shrink=TRUE, labeller="label_value", as.table=TRUE, drop=TRUE)

Let us first create a regular pie chart

Program 1 : Regular Pie Chart

x <- c(3,3,2,1,1)

labels <- c('ADA','CN','PDS','CPDP','PE')

pie(x, labels, main="Credits of subjects", col=rainbow(length(x)))

Output:

For building a Pie Chart in R, we can use ggplot2 package, but it does not have a direct method to do so. Instead, we plot a bar graph and then convert it into Pie Chart using coord_polar() function. 

Approach:

• Import library
• Create data
• Create dataframe
• Plot a bar graph
• Convert bar graph into Pie chart
• Remove numerical values and grid

Program 2: Pie Chart using ggplot2

library(ggplot2)

df = data.frame(x <- c(3,3,2,1,1),
                labels <- c('ADA','CN','PDS','CPDP','PE'))

ggplot(df, aes(x="", y=x, fill=labels)) +geom_bar(width = 1, stat = "identity") +
  coord_polar("y", start=0) +theme_void()

Output:

To plot multiple pie charts in R using ggplot2, we have to use an additional method named facet_grid(). This method forms a matrix defined by row and column faceting variables. When we have two different variables and need a matrix with all combinations of these two variables, we use this method.

Approach:

• Import library
• Create dataframe
• Convert variables into categorical variables
• Plot Bar graph
• Convert into Pie Chart
• Add facet_grid()

Program 3: Multiple Pie Chart 

library(ggplot2)
df = data.frame(subject <- c('ADA','ADA','ADA','CN','CN','CN','PDS','PDS','PDS','CPDP',
                         'CPDP','CPDP'),
                credit <- c('Midsem','Viva','Attendance','Midsem','Viva','Attendance',
                            'Midsem','Viva','Attendance','Midsem','Viva','Attendance'),
                value <- c(50,30,20,40,40,20,50,35,15,50,40,10))

df$subject <- factor(df$subject)
df$credit <- factor(df$credit) 

ggplot(data=df, aes(x=" ", y=value, group=credit, colour=credit, fill=credit)) +
         geom_bar(width = 1, stat = "identity") +
         coord_polar("y", start=0) + 
         facet_grid(.~ subject) +theme_void()

Output:

We can also plot multiple pie charts in the form of a donut chart using ggplot2 in R. 

Approach:

• Import library
• Create dataframe
• Convert variables into categorical variables
• Plot Bar graph using geom_col()
• Add an empty element before the subjects using scale_x_discrete()
• Convert into Pie Chart using coord_polar()

Program 4: Multiple Pie Chart/ Donut Chart 

library(ggplot2)
df = data.frame(subject <- c('ADA','ADA','ADA','CN','CN','CN','PDS','PDS','PDS'),
                credit <- c('Midsem','Viva','Attendance','Midsem','Viva','Attendance',
                            'Midsem','Viva','Attendance'),
                value <- c(50,30,20,40,40,20,50,35,15))

df$subject <- factor(df$subject) # converts to a categorical variable
df$credit <- factor(df$credit) # converts to a categorical variable


ggplot(df, aes(x = subject, y = value, fill = credit)) +
  geom_col() +scale_x_discrete(limits = c(" ", "ADA","CN","PDS")) +coord_polar("y")

Output: