In Part 14, let’s see how to create pie charts in R. Let’s create a simple pie chart using the pie() command. As always, we set up a vector of numbers and then we plot them.
B <- c(2, 4, 5, 7, 12, 14, 16)
Create a simple pie chart.
pie(B)

Now let’s create a pie chart with a heading, using nice colours, and define our own labels using R’s
rainbow() palette. We control the number of colours using length(B).
pie(B, main="My Piechart", col=rainbow(length(B)), labels=c("Mon","Tue","Wed","Thu","Fri","Sat","Sun"))

Here is a more complex example, using percentages and a legend. We create a vector of data, one for each day of the week
B <- c(5, 3, 1, 8, 9, 4, 6)
Set up black, grey and white for clear printing.
cols <- c("grey90","grey50","black","grey30","white","grey70","grey50")
Calculate the percentage for each day, using one decimal place.
percentlabels <- round(100*B/sum(B), 1)
Add a ‘%’ sign to each percentage value using the paste() command.
pielabels <- paste(percentlabels, "%", sep="")
What does the paste() command do?
pie(B, main="My Best Piechart", col=cols, labels=pielabels, cex=0.8)
Create a legend at the top-right.
legend("topright", c("Mon","Tue","Wed","Thu","Fri","Sat","Sun"), cex=0.8, fill=cols)
Here is your pie chart:

OK. Now let’s create a pie chart from a data frame and include sample sizes. First create a table of counts of cylinder numbers from the mtcars dataset.
cyltable <- table(mtcars$cyl)
cyltable

We have eleven cars with four cylinders, seven cars with six cylinders, and fourteen cars with eight cylinders.
Now we create labels.
labs <- paste("(",names(cyltable),")", "\n", cyltable, sep="")
Now we plot.
pie(cyltable, labels = labs, col = c("red", "yellow", "blue"), main="Pie chart of cylinder numbers\n with sample sizes")

That wasn’t so hard! In Blog 15 we will look at further plotting techniques in R.
See you later!
David

Annex: R codes used

[code lang=”r”]
# Create a vector with numbers.
B <- c(2, 4, 5, 7, 12, 14, 16)

# Create a simple pie chart.
pie(B)

# Create a pie chart with rainbow colours.
pie(B, main="My Piechart", col=rainbow(length(B)), labels=c("Mon","Tue","Wed","Thu","Fri","Sat","Sun"))

# Create a vector with numbers.
B <- c(5, 3, 1, 8, 9, 4, 6)

# Set up black, grey and white for clear printing.
cols <- c("grey90","grey50","black","grey30","white","grey70","grey50")

# Calculate the percentage for each day, using one decimal place.
percentlabels <- round(100*B/sum(B), 1)

# Add a ‘%’ sign to each percentage value using the paste command.
pielabels <- paste(percentlabels, "%", sep="")

# Create a pie chart.
pie(B, main="My Best Piechart", col=cols, labels=pielabels, cex=0.8)

# Add a legend at the right to existing pie chart.
legend("topright", c("Mon","Tue","Wed","Thu","Fri","Sat","Sun"), cex=0.8, fill=cols)

# Create a table of counts of cylinder numbers from the mtcars dataset.
cyltable <- table(mtcars$cyl)
cyltable

# Create labels.
labs <- paste("(",names(cyltable),")", "\n", cyltable, sep="")

# Create a pie chart.
pie(cyltable, labels = labs, col = c("red", "yellow", "blue"), main="Pie chart of cylinder numbers\n with sample sizes")
[/code]