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Learn how to create awesome data visualizations using the most popular Python libraries, such as matplotlib, seaborn and plotly.
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Yes! I also believe that to be the case. Nevertheless, researchers who publish papers may opt to go with matplotlib because personalisation is easier.
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Look at the following example as an aspiration you can achieve if you fully understand and replicate this whole tutorial with your data.
Let's load a dataset that contains information from countries (rows) considering socio-demographic and economic variables (columns).
import plotly.express as px
df_countries = px.data.gapminder()
df_countries
Python contains 3 main libraries for Data Visualization:
Matplotlib (Mathematical Plotting)
Seaborn (High-Level based on Matplotlib)
Plotly (Animated Plots)
I love plotly because the Visualizations are interactive; you may hover the mouse over the points to get information from them:
df_countries_2007 = df_countries.query('year == 2007')
px.scatter(data_frame=df_countries_2007, x='gdpPercap', y='lifeExp',
color='continent', hover_name='country', size='pop')
You can even animate the plots with a simple parameter. Click on play ↓
PS: The following example is taken from the official plotly library website:
px.scatter(df_countries, x="gdpPercap", y="lifeExp", animation_frame="year", animation_group="country",
size="pop", color="continent", hover_name="country",
log_x=True, size_max=55, range_x=[100,100000], range_y=[25,90])
In this article, we'll dig into the details of Data Visualization in Python to build up the required knowledge and develop awesome visualizations like the ones we saw before.
Matplotlib is a library used for Data Visualization.
We use the sublibrary (module) pyplot from matplotlib library to access the functions.
import matplotlib.pyplot as plt
Let's make a bar plot:
plt.bar(x=['Real Madrid', 'Barcelona', 'Bayern Munich'],
height=[14, 5, 6]);
We could have also done a point plot:
plt.scatter(x=['Real Madrid', 'Barcelona', 'Bayern Munich'],
y=[14, 5, 6]);
But it doesn't make sense with the data we have represented.
Let's create a DataFrame:
teams = ['Real Madrid', 'Barcelona', 'Bayern Munich']
uefa_champions = [14, 5, 6]
import pandas as pd
df_champions = pd.DataFrame(data={'Team': teams,
'UEFA Champions': uefa_champions})
df_champions
And visualize it using:
plt.bar(x=df_champions['Team'],
height=df_champions['UEFA Champions']);
df_champions.plot.bar(x='Team', y='UEFA Champions');
Let's read another dataset: the Football Premier League classification for 2021/2022.
df_premier = pd.read_excel(io='../data/premier_league.xlsx')
df_premier
We will visualize a point plot, from now own scatter plot to check if there is a relationship between the number of goals scored F versus the Points Pts.
import seaborn as sns
sns.scatterplot(x='F', y='Pts', data=df_premier);
Can we do the same plot with matplotlib plt library?
plt.scatter(x='F', y='Pts', data=df_premier);
Which are the differences between them?
The points: matplotlib points are bigger than seaborn ones
The axis labels: matplotlib axis labels are non-existent, whereas seaborn places the names of the columns
From which library do the previous functions return the objects?
seaborn_plot = sns.scatterplot(x='F', y='Pts', data=df_premier);
matplotlib_plot = plt.scatter(x='F', y='Pts', data=df_premier);
type(seaborn_plot)
matplotlib.axes._subplots.AxesSubplot
type(matplotlib_plot)
matplotlib.collections.PathCollection
Why does seaborn returns a matplotlib object?
Quoted from the seaborn official website:
Seaborn is a Python data visualization library based on matplotlib. It provides a high-level* interface for drawing attractive and informative statistical graphics.
*High-level means the communication between humans and the computer is easier to understand than low-level communication, which goes through 0s and 1s.
Could you place the names of the teams in the points?
plt.scatter(x='F', y='Pts', data=df_premier)
for idx, data in df_premier.iterrows():
plt.text(x=data['F'], y=data['Pts'], s=data['Team'])
It isn't straightforward.
Is there an easier way?
Yes, you may use an interactive plot with plotly library and display the name of the Team as you hover the mouse on a point.
We use the express module within plotly library to access the functions of the plots:
import plotly.express as px
px.scatter(data_frame=df_premier, x='F', y='Pts', hover_name='Team')
Learn how to become an independent Data Analyist programmer who knows how to extract meaningful insights from Data Visualizations.
Let's read another dataset: the sociological data of clients in a restaurant.
df_tips = sns.load_dataset(name='tips')
df_tips
df_tips.sex
0 Female 1 Male ...
242 Male 243 Female Name: sex, Length: 244, dtype: category Categories (2, object): ['Male', 'Female']
We need to summarise the data first; we count how many Female and Male people are in the dataset.
df_tips.sex.value_counts()
Male 157 Female 87 Name: sex, dtype: int64
sr_sex = df_tips.sex.value_counts()
Let's place bars equal to the number of people from each gender:
px.bar(x=sr_sex.index, y=sr_sex.values)
We can also colour the bars based on the category:
px.bar(x=sr_sex.index, y=sr_sex.values, color=sr_sex.index)
Let's put the same data into a pie plot:
px.pie(names=sr_sex.index, values=sr_sex.values, color=sr_sex.index)
df_tips.total_bill
0 16.99 1 10.34 ...
242 17.82 243 18.78 Name: total_bill, Length: 244, dtype: float64
Instead of observing the numbers, we can visualize the distribution of the bills in a histogram.
We can observe that most people pay between 10 and 20 dollars. Whereas a few are between 40 and 50.
px.histogram(x=df_tips.total_bill)
We can also create a boxplot where the limits of the boxes indicate the 1st and 3rd quartiles.
The 1st quartile is 13.325, and the 3rd quartile is 24.175. Therefore, 50% of people were billed an amount between these limits.
px.box(x=df_tips.total_bill)
df_tips[['total_bill', 'tip']]
We use a scatter plot to see if a relationship exists between two numerical variables.
Do the points go up as you move the eyes from left to right?
As you may observe in the following plot: the higher the amount of the bill, the higher the tip the clients leave for the staff.
px.scatter(x='total_bill', y='tip', data_frame=df_tips)
Another type of visualization for 2 continuous variables:
px.density_contour(x='total_bill', y='tip', data_frame=df_tips)
df_tips[['day', 'total_bill']]
We can summarise the data around how much revenue was generated in each day of the week.
df_tips.groupby('day').total_bill.sum()
day Thur 1096.33 Fri 325.88 Sat 1778.40 Sun 1627.16 Name: total_bill, dtype: float64
sr_days = df_tips.groupby('day').total_bill.sum()
We can observe that Saturday is the most profitable day as people have spent more money.
px.bar(x=sr_days.index, y=sr_days.values)
px.bar(x=sr_days.index, y=sr_days.values, color=sr_days.index)
df_tips[['day', 'size']]
Which combination of day-size is the most frequent table you can observe in the restaurant?
The following plot shows that Saturdays with 2 people at the table is the most common phenomenon at the restaurant.
They could create an advertisement that targets couples to have dinner on Saturdays and make more money.
px.density_heatmap(x='day', y='size', data_frame=df_tips)
The following examples are taken directly from plotly.
df_gapminder = px.data.gapminder()
px.scatter_geo(df_gapminder, locations="iso_alpha", color="continent", #!
hover_name="country", size="pop",
animation_frame="year",
projection="natural earth")
import plotly.express as px
df = px.data.election()
geojson = px.data.election_geojson()
fig = px.choropleth_mapbox(df, geojson=geojson, color="Bergeron",
locations="district", featureidkey="properties.district",
center={"lat": 45.5517, "lon": -73.7073},
mapbox_style="carto-positron", zoom=9)
fig.update_layout(margin={"r":0,"t":0,"l":0,"b":0})
import plotly.express as px
df = px.data.election()
geojson = px.data.election_geojson()
fig = px.choropleth_mapbox(df, geojson=geojson, color="winner",
locations="district", featureidkey="properties.district",
center={"lat": 45.5517, "lon": -73.7073},
mapbox_style="carto-positron", zoom=9)
fig.update_layout(margin={"r":0,"t":0,"l":0,"b":0})