Visualization

Tutorial for Line Plot in R using ggplot2 with Examples

October 24, 2021

Contents

1 Introduction
2 Syntax of Line Plot in ggplot2
3 Examples of Line Plot in R using ggplot2

Introduction

In this article, we will go through the tutorial for drawing Line Plot in R with ggplot2 package. ggplot2 is a commonly used open-sourced R package for creating beautiful visualizations. We will first explain the syntax for geom_line() geometric object that is used for generating line plots in ggplot2. And then we will present different kinds of examples for creating the line plots with this library.

Syntax of Line Plot in ggplot2

The minimal syntax for generating a line plot in ggplot2 is

ggplot(<data>, mapping = aes(<mapping>) + geom_line()

However, for better visualization and aesthetic looks, the more common practice is to add scatter plot points with the line plot as below –

ggplot(<data>, mapping = aes(<mapping>) + geom_line() + geom_point()

Deep Learning Specialization on Coursera

ggplot2 lets you add more layers to the plot such as theme, labs, etc. to create more advanced scatter plots.

Also Read – Learn Scatter Plot in R using ggplot2 with Examples

Examples of Line Plot in R using ggplot2

Loading ggplot2 Library

We start by loading the ggplot2 library as shown below.

In[0]:

library(ggplot2)

Loading Dataset

We are going to use the cars dataset for all examples of line plot. The dataset is loaded into the data frame and its sample rows are shown.

In [1]:

df <- read.table("Cars.csv",header=TRUE,sep=',') 
options( warn = -1 )
head(df)

Out[1]:

name	year	selling_price	km_driven	fuel	seller_type	transmission	owner
Maruti 800 AC	2007	60000	70000	Petrol	Individual	Manual	First Owner
Maruti Wagon R LXI Minor	2007	135000	50000	Petrol	Individual	Manual	First Owner
Hyundai Verna 1.6 SX	2012	600000	100000	Diesel	Individual	Manual	First Owner
Datsun RediGO T Option	2017	250000	46000	Petrol	Individual	Manual	First Owner
Honda Amaze VX i-DTEC	2014	450000	141000	Diesel	Individual	Manual	Second Owner
Maruti Alto LX BSIII	2007	140000	125000	Petrol	Individual	Manual	First Owner

Example 1: Basic Line plot in ggplot2

Let us plot the basic ggplot2 line plot using the geom_line() for the first 10 records of the dataset for ‘year’ vs ‘selling_price’

In [2]:

# Basic line plot with points

ggplot(data=head(df, n=20), aes(x=year, y=selling_price)) +
  geom_line()+
  geom_point()

Out[2]:

Example 2: Change Line type

The type of the line plot can be changed by passing the linetype parameter that has several options like dotted, two dashes, dashed, etc.

In the following two examples, we have used ‘dashes’ and ‘twodashes’ in the linetype parameter.

In [3]:

# Change the line type
ggplot(data=head(df, n=10), aes(x=year, y=selling_price)) +
  geom_line(linetype = "dashed")+
  geom_point()

Out[3]:

In [4]:

ggplot(data=head(df, n=200), aes(x=year, y=selling_price)) +
  geom_line(linetype = "twodash")+
  geom_point()

Out[4]:

Example 3: Change line color

Let’s change the line color using the color parameter of geom_line( ). In the below example, we have used red color.

In [5]:

# Change the color
ggplot(data=head(df, n=10), aes(x=year, y=selling_price, group=1)) +
  geom_line(color="red")+
  geom_point()

Out[5]:

Example 4: Change the size of the Line Plot in ggplot2

The line size can be customized using the command size and passing the value of the size inside geom_line( ).

In [6]:

# Format the line size
ggplot(data=head(df, n=10), aes(x=Country, y=Urban.Pop, group=1)) +
  geom_line(color="green",size=1.5)+
  geom_point()

Out[6]:

Example 5: Add Titles to Line plot

ggtitle() can be used to add plot title and labs() can be used to add axes title.

In [7]:

line<-ggplot(data=head(df, n=10), aes(x=Country, y=Urban.Pop, group=1)) +
  geom_line(color="blue",size=1.1)+
  geom_point() + 
  ggtitle("Kilometres vs Car Price")+
  labs(x="KM",y="Price")

Out[7]:

Example 6: Add Arrows to the Line Plot

To add an arrow to our line we use the arrow parameter and pass it an arrow( ).

We can also change the parameters in an arrow-like angle, type ends in the arrow object as shown in the second example below.

In [8]:

# Adding an arrow
ggplot(data=head(df, n=10), aes(x=Country, y=Land.Area, group=1)) +
  geom_line(arrow=arrow(),size=1.1,color='red')+
  geom_point()

Out[8]:

In [9]:

# Adding  closed arrow on both ends of the line
arr=arrow(angle = 20, ends = "both", type = "closed")
ggplot(data=head(df, n=10), aes(x=Country, y=Land.Area, group=1)) +
  geom_line(arrow=arr,size=1.1,color='red')+
  geom_point()

Out[9]:

Example 7: Multiple Line Plots

To plot multiple line plots in one graph, we don’t have to change much except the group attribute has to be set to the name of the column based on which different lines will be plotted

In [10]:

# Color selection
cols <- c("#D43F3A", "#EEA236")

ggplot(df, aes(x =year, y =selling_price , color =transmission)) +
  geom_line(size=3) +
  scale_color_manual(values = cols) + theme_dark()

Out[10]:

Example 8: Legend Customization

We can change the title of our legend of the line plot using the guide_legend() function as shown below.

In [11]:

ggplot(df, aes(x =year,y=selling_price , color =transmission)) +
  geom_line(size=2.5) +
  guides(color = guide_legend(title = "The Title"))

Out[11]:

Here we change the Legend Labels:

In [12]:

ggplot(df, aes(x =year,y=selling_price , color =transmission)) +
  geom_line(size=2.5) +
  scale_color_discrete(labels = paste("Transmission Type", 1:2))

Out[12]:

Example 9: Creating Line Plot based on Conditions

We can create the line plot for the dataset based on the condition that the selling_price for cars that have driven less than 100 thousand kilometers.

In [13]:

ss <- subset(head(df,n=30), km_driven<100000)
ggplot(data = ss, aes(x=km_driven, y=selling_price)) + geom_line(size=2.5, color='red')

Out[13]:

Example 10: Adding Data Labels in Line Plot

Now let us add some data labels, here we use labels to get the values in the y-axis and nudge_y to place the data label.

In [14]:

ggplot(data=head(df,n=8), aes(x=year, y=selling_price, group=1,label=selling_price)) +
  geom_line(color='blue',size=2.5)+
  geom_point()+
  geom_text(nudge_y = 3, size=6)