How to plot line chart in R using ggplot?
This recipe helps you plot line chart in R using ggplot
Recipe Objective
A line chart is a type of chart which showcases information as a sequency of data points also known as 'markers' which are connected by staright line. It is mainly used to plot the relationship or trend of a categorical variable with respect to a numerical variable.
In this recipe we are going to use ggplot2 package to plot the required Line Chart. ggplot2 package is based on the book "Grammar of Graphics" by Wilkinson. This package provides flexibility while incorporating different themes and plot specification with a high level of abstraction. The package mainly uses aesthetic mapping and geometric objects as arguments. Different types of geometric objects include:
- geom_point() - for plotting points
- geom_bar() - for plotting bar graph
- geom_line() - for plotting line chart
- geom_histogram() - for plotting histogram
The basic syntax of gggplot2 plots is:
ggplot(data, mapping = aes(x =, y=)) + geometric object
where:
- data : Dataframe that is used to plot the chart
- mapping = aes() : aesthetic mapping which deals with controlling axis (x and y indicates the different variables)
- geometric object : Indicates the code for typeof plot you need to visualise.
This recipe demonstrates how to make a Line Chart using ggplot2.
STEP 1: Loading required library and creating dataset
We will use an example of no of schools established in 2 states between 1970 and 2014
# Data manipulation package
library(tidyverse)
# ggplot for data visualisation
library(ggplot2)
# years
year = c('1970','1980', '1990', '2000', '2013', '2014')
#no of schools in state1 corresponding to a particular year
no_of_schools_state1 = c(15, 30, 60, 120, 240, 300)
#creating a dataframe
df = data.frame(year_x,state_y1)
df
year_x state_y11970 15 1980 30 1990 60 2000 120 2013 240 2014 300
STEP 2: Plotting a Line Chart using ggplot
We use geometric object as geom_line() to plot a line chart between two variables (Age and Customer ID)
Note:
- The + sign in the syntax earlier makes the code more readable and enables R to read further code without breaking it.
- We also use labs() function to give a title to the graph
- group arguement is kept at 1 as just one obsrvation is present for each year.
ggplot(df, mapping = aes(x = year, y = no_of_schools_state1, group = 1)) + geom_line() + labs(title = "No of schools vs Year")
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