Graphing with Python using Matplotlib

 Introduction

Matplotlib is a graphing and plotting library that can be useful for creating different types of graphs and plots. Such as line charts, pie charts, scatter plots and 3D plots. Matplotlib can also be used for creating animated and interactive visualizations. It can also generate output in a variety of formats which includes PNG, SVG and PDF etc.

Installing Matplotlib

Matplotlib is not built into python. First, we need to install Matplotlib using the PIP package manager.

pip install matplotlib

If you are using Conda you can use the below command.

conda install matplotlib

You can refer to more about installation options on the Matplotlib installation page.

Plotting Simple Graph using Matplotlib

First, we need to import pyplot from Matplotlib library.  After that line, we give 2 python lists as arguments to plot() function specifying Y values and X values for the graph. then we set the label for both the x and y axis and the title. Finally, we call the show() function that displays our plot in a window.

#importing pyplot from matplotlib library
import matplotlib.pyplot as pyplot

# plot the graph using given values
pyplot.plot(
	[1, 2, 3, 4], # Y values
	[0.5, 1.0, 1.5, 2.0] # X values
)

# setting x and y axis labels
pyplot.xlabel('x-axis-label') 
pyplot.ylabel('y-axis-label')

# setting the title
pyplot.title('This is the title')

# display the chart in a window
pyplot.show()

 simple graph using matplotlib

Plotting Multiple Graphs Same Plane.

When plotting multiple graphs we need to add different styles, and colours, and more importantly, we need to add a legend to identify each graph clearly. In the below code sample, we add a legend using legend() method and pass arguments for legend background colour, location and title. we also add a descriptive label for each graph, change the colour and set the style of the one graph to a dashed line.

    

import matplotlib.pyplot as pyplot

# plot the graph 1
pyplot.plot(
	[0, 1, 2, 3], # Y values
	[1, 3, 5, 7], # X values
	label = 'y = 2x + 1', # set the label
	color = 'blue' # set the color
)

# plot the graph 2
pyplot.plot(
	[0, 1, 2, 3], # Y values
	[3, 6, 9, 12], # X values
	ls = '--', # set the line style
	label = 'y = 3x + 3', # set the label 
	color = '#995789' # set color color
)
# setting x and y axis labels
pyplot.xlabel('x-axis-label') 
pyplot.ylabel('y-axis-label')

# setting the title
pyplot.title('This is the title')

# setting the legend
pyplot.legend(
	facecolor = 'gray', # legend background
	title = 'legend', # legend title
	loc = 'upper left' # legend location
)

# setting the grid line
pyplot.grid(True)

# display the chart in a window
pyplot.show()

multiple graphs in the same plane

Plotting Bar Chart

We use the matplotlib pyplot bar() function to draw bar graphs. In the below examples, we pass the x-coordinates, heights of each bar,  bar width, and colours of each bar.

import matplotlib.pyplot as plt

languages= ['Rust', 'Python', 'Kotlin', 'Javascript', 'C#']
#setting values for bar labels
Salary = [76000, 60000, 55000, 56000, 61000]
# bar colors
bar_colors = ['blue', 'orange', 'cyan', 'brown', 'purple']

# setting the bar chart
plt.bar(
	languages, # x coordinates 
	Salary, # heights of the bars
	width = 0.7, # width of the bars
	color = bar_colors # bar colors
)

plt.xlabel('Language')
plt.ylabel('Salary')
plt.title('Median Developer Salary By Language')

plt.show()

Bar chart matplotlib

Horizontal Bar Charts

You can create the above graph horizontal by using barh() matplotlib pyplot function instead of bar() function. The below code demonstrates it.

import matplotlib.pyplot as plt

languages= ['Rust', 'Python', 'Kotlin', 'Javascript', 'C#']
#setting values for bar labels
Salary = [76000, 60000, 55000, 56000, 61000]
# bar colors
bar_colors = ['blue', 'orange', 'cyan', 'brown', 'purple']

# setting the bar chart
plt.barh(
	languages, # y coordinates 
	Salary, # width of the bars
	height = 0.7, # height of the bars
	color = bar_colors # bar colors
)

plt.xlabel('Salary')
plt.ylabel('Language')
plt.title('Median Developer Salary By Language')

plt.show()

Horizontal bar graph matplotlib

Line Graphs using Matplotlib

In the below line graph example, we pass the argument 'bo-' to the function. in this argument 'bo-' first character 'b' indicates the colour of the line and second character 'o' indicates the marker of each point being plotted and the third character  '-' indicates the line style of the graph. In our case, it sets to a blue solid line with circle markers.

import matplotlib.pyplot as plt

month = ['January', 'February', 'March', 'April', 'May', 'June']
profit = [10000, 28000, 13400, 14000, 24400, 21000]

# setting titles and axes headings.
plt.title('Profit in year 2022')
plt.xlabel('Month')
plt.ylabel('Profit')

plt.plot(
	month, # setting x values 
	profit, # setting y values
	'bo-' # style of the graph(color, marker, line style)
)

plt.show()

Line Graph Matplotlib

Scatter plot

we use Matplotlib scatter() function to draw a scatter plot. below code sample demonstrates a scatter plot.

import matplotlib.pyplot as plt

iq = [
	[43, 45, 57, 20, 30, 75, 29, 60, 27, 80], # Age
	[22, 46, 43, 23, 45, 76, 44, 56, 41, 62] # IQ score
]

maths = [
	[29, 70, 20, 57, 30, 44, 60, 25, 32, 62], # Age
	[40, 23, 90, 55, 80, 39, 74, 65, 87, 48] # Maths score
]

# plot iq data
plt.scatter(
	x = iq[0], 
	y = iq[1],
	color='darkorange',
	marker='o',
	label='IQ'
)

# plot maths data
plt.scatter(
	x = maths[0], 
	y = maths[1],
	color='green',
	marker='^',
	label='Mathematics'
)

plt.xlabel('Age')
plt.ylabel('Score')
plt.title('Marks Two Subjects')
plt.legend()

plt.show()

Scatter Plot

Pie chart

Matplotlib pyplot pie() function was used to draw below the pie chart. 

import matplotlib.pyplot as plt

language = ['Python', 'Rust', 'Java', 'C#', 'Javascript']
precentage = [33.50, 15.30, 22.30, 12.45, 16.45]

plt.pie(
	precentage,
	labels = language,
	autopct = '%1.2f%%', # format the numeric values in wedges
	counterclock = False, # wedges plot direction
	startangle = 90 # starting angle 
)

plt.title('Language Popularity')

plt.show()

Pie chart

Conclusion

In this article, we show you how to draw simple graphs using the Matplotlib library. Matplotlib is a very flexible option for creating graphs in python. 

References

• Matplotlib documentation - https://matplotlib.org/stable/