In this tutorial, we learn to create univariate bar plots using the Graphics package in R. We also learn to modify graphical parameters associated with the bar plot.

1. www.r-squared.in/git-hub
R2
Academy
Data Visualization With R:
Univariate Bar Plots

2. R2
AcademyCourse Material
Slide 2
All the material related to this course are available on our website
Scripts can be downloaded from GitHub
Videos can be viewed on our Youtube Channel

3. R2
AcademyTable Of Contents
Slide 3
➢ Objectives
➢ Introduction
➢ Simple bar plot
➢ Bar width
➢ Space between bars
➢ Bar Labels
➢ Horizontal Bars
➢ Density of shading lines
➢ Angle of shading lines
➢ Color
➢ Legend
➢ Border color
➢ Display/Hide vertical axes
➢ Display/Hide labels
➢ Modify font size of numeric (vertical Y) axis
➢ Modify font size of categorical(horizontal X) axis
➢ Line Type of horizontal axis
➢ Modify values of numeric (vertical Y) axis
➢ Summary

4. R2
AcademyObjectives
Slide 4
➢ Create univariate bar plots
➢ Modify width, space and color of bars
➢ Add legend to the plot
➢ Modify appearance of the axis
Note: In this tutorial, we use the Graphics package.

5. R2
AcademyIntroduction
Slide 5
A bar chart or bar graph is a chart that presents Grouped data with rectangular bars with lengths proportional to the
values that they represent. The bars can be plotted vertically or horizontally. A vertical bar chart is sometimes called a
column bar chart.
- Wikipedia

6. R2
AcademySimple Bar Plot
Slide 6
In the Graphics package, the barplot function
is used to create bar plots. You can learn more
about this function from the help pages:
help(barplot)
To create a bar plot, we first tabulate the data
using the table function and then use the
tabulated data as the input.
# basic bar plot
data <- table(mtcars$cyl)
barplot(data)

7. R2
AcademyBar Width
Slide 7
The width of the bars can be modified using the
width option in the barplot function.
In the below example, we specify the width of
the middle bar to be twice that of the other two
bars.
# specify width of bars
data <- table(mtcars$cyl)
barplot(data, width = c(1, 2, 1))

8. R2
AcademySpace Between Bars
Slide 8
The space between the bars can be modified
using the space option in the barplot
function.
In the below example, we specify the space
between the bars to be 1.5
# specify space between bars
data <- table(mtcars$cyl)
barplot(data, space = 1.5)

9. R2
AcademySpace Between Bars
Slide 9

10. R2
AcademyLabels
Slide 10
The labels of the bars can be modified using
the names.arg option in the barplot function.
The names must be specified using a character
vector, the length of which should be equal to
the number of bars.
# specify labels for bars
data <- table(mtcars$cyl)
barplot(data, names.arg = c("Four",
"Six", "Eight"))

11. R2
AcademyHorizontal Bars
Slide 11
Horizontal bar plots can be created using the
horiz option in the barplot function. If it is
set to TRUE, horizontal bars are drawn else
vertical bars are drawn.
Note: The default value of this option is FALSE.
# horizontal bars
data <- table(mtcars$cyl)
barplot(data, horiz = TRUE)

12. R2
AcademyShading Lines (Density)
Slide 12
Shading lines can be drawn on the bars using
the density option in the barplot function. It
takes positive values and the density of the
lines increases in proportion to the values
specified.
Note: The default value of this option is NULL.
Lines will not be drawn if negative values are
specified.
# specify density of shading lines
data <- table(mtcars$cyl)
barplot(data, density = 10)

13. R2
AcademyShading Lines (Density)
Slide 13

14. R2
AcademyShading Lines (Angle)
Slide 14
The angle of the shading lines drawn on the
bars can be modified using the angle option in
the barplot function. It takes both positive and
negative values.
# specify angle of shading lines
data <- table(mtcars$cyl)
barplot(data, density = 10, angle = 60)

15. R2
AcademyShading Lines (Angle)
Slide 15

16. R2
AcademyColor
Slide 16
The color of the bars can be modified using the
col option in the barplot function. The color
can be mentioned in RGB or hexadecimal
format as well.
# specify color of bars
data <- table(mtcars$cyl)
barplot(data, col = "blue")

17. R2
AcademyColor
Slide 17
Different colors for the bars can be created by
specifying a character vector consisting of the
names of the colors. If the number of colors
mentioned is less than the number of bars, the
colors will be repeated.
# specify different color for bars
data <- table(mtcars$cyl)
barplot(data, col = c("red", "green",
"blue"))

18. R2
AcademyLegend
Slide 18
A legend can be added using the legend.text
option. If it is set to TRUE, a legend is added
based on the values associated with the bars.
We can also specify a character vector in which
case the legend will be created on the basis of
the input specified. We will explore legends in
more detail in a separate tutorial.
# specify legend
data <- table(mtcars$cyl)
barplot(data, col = c("red", "green",
"blue"), legend.text = TRUE)

19. R2
AcademyBorder Color
Slide 19
The border color of the bars can be modified
using the border option in the barplot
function. The color can be mentioned in RGB or
hexadecimal format as well.
# specify border color of bars
data <- table(mtcars$cyl)
barplot(data, border = "blue")

20. R2
AcademyBorder Color
Slide 20
Different colors for the borders can be created
by specifying a character vector consisting of
the names of the colors. If the number of colors
mentioned is less than the number of bars, the
colors will be repeated.
# specify different border color
data <- table(mtcars$cyl)
barplot(data, border = c("red",
"green", "blue"))

21. R2
AcademyTitle, Axis Labels & Range
Slide 21
We can add a title and modify the axis labels
and range using the options we learnt in the
earlier tutorials.
# specify title, axis labels and range
data <- table(mtcars$cyl)
barplot(data, col = c("red", "green", "blue"),
main = "Frequency of Cylinders",
xlab = "Number of Cylinders",
ylab = "Frequency", ylim = c(0, 20))

22. R2
AcademyAxes
Slide 22
The vertical axes is not drawn if the axes option is set to FALSE. The default value is TRUE and hence a
vertical axes is always drawn unless specified otherwise.

23. R2
AcademyAxis Names
Slide 23
The labels of the bars are not added if the axisnames option is set to FALSE. The default value is TRUE
and hence the labels are always added unless specified otherwise.

24. R2
AcademyNumeric Axis Font Size
Slide 24
The font size of the
numeric axis can
be modified using
the cex.axis
option.

25. R2
AcademyLabels Font Size
Slide 25
The font size of the
labels can be
modified using the
cex.names option.

26. R2
AcademyAxis Line Type
Slide 26
A line type for the
horizontal axis can
be specified using
axis.lty option.

27. R2
AcademyOffset
Slide 27
The values of the
numeric (vertical Y)
axis can be
modified using the
offset option.

28. R2
Academy
Slide 28
● Bar plots can be created using the barplot() function.
● Tabulate the data using the table() function before plotting.
● Modify the width of the bars using the width option.
● Modify the space between the bars using the space option.
● Modify the labels of the bars using the names.arg option.
● Create horizontal bars using the horiz option.
● Add shading lines using the density option and modify the angle of the lines using the angle
option.
● Add color to the bars using the col and border options.
● Add legend to the plot using the legend.text option.
● Display/hide the numeric axis using the axes option.
● Display/hide the labels using the axis.names option.
● Modify font size of the numeric axis using the cex.axis option.
● Modify font size of the labels using the cex.names option.
● Modify line type of the horizontal axis using the axis.lty option.
● Modify values of the numeric axis using the offset option.
Summary

29. R2
AcademyNext Steps...
Slide 29
In the next module:
✓ Bivariate Bar Plots
✓ Stacked Bar Plots
✓ Grouped Bar Plots

30. R2
Academy
Slide 30
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