Prerequisite: Altair
In this article, We will see Stacked Bar Chart With Selection with Altair python. It is a declarative and interactive visualization tool for Python, based on Visualization Grammar (VeGa), It is simple, user-friendly, and moreover provides clearly interpretable charts. It supports a wide variety of charts like bar, line, scatter, box, violin, and other charts in an interactive way. Let’s discuss how to create a stacked bar chart with a selection to highlight a particular stack of the bar chart.
Installation
The following command can be used to install Altair and Pandas like any other python library:
pip install altair pip install pandas pip install altair_viewer
Functions Used
- The altair.selection_single() specify the type of selection inside the select method. The method takes parameters that are discussed below.
Syntax: altair.selection_single(type, encodings)
- type – string. Determines the default event processing and data query for the selection. Three types single, multi (shift+ click), interval (drag).
- encodings – List of encoding channels. The corresponding data field values must match for a data tuple to fall within the selection.
- The encode() method is used to map columns to visual attributes of the plot. This method takes in parameters of the x and y-axis and other chart attributes. The mark property is what specifies how exactly those attributes should be represented on the plot.
Syntax: alt.Chart(data).mark_bar().encode(x, y, color)
- x – The x-axis value
- y – The y-axis value
- color – The color of the mark
Implementation
Import the Altair and pandas package. Read the dataset using pandas and specify the type of selection we have used the selection_single() method. Then, pass the dataset to the chart() function and make use of the mark_bar().encode() method to pass the x and y-axis values and append the selection object after passing the parameters to the mark_bar() function.
Example 1:
The dataset used for demonstration purposes can be downloaded from here.
Python3
import altair as alt import pandas as pd # load the data source = pd.read_csv("test.csv") # specify the type of selection, here single selection is used selector = alt.selection_single(encodings=['x', 'color']) # use mark_bar function to plot a stacked bar and specify x and y axis chart = alt.Chart(source).mark_bar().encode( x='State', y='sum(Vote %)', color=alt.condition(selector, 'Party', alt.value('lightgray')) ).add_selection( selector ) # initializer altair_viewer to display the interactive chart alt.renderers.enable('altair_viewer') chart.show() |
Output:
Stacked bar chart
To see the interactive visualization, run the code and it will automatically redirect you to an interactive webpage.
Example 2:
The pandas DataFrame is used for demonstration purposes.
Python3
import altair as alt import pandas as pd # creating a custom dataframe data = pd.DataFrame([[254, 'Subham', 'ODI'], [153, 'Amit', 'ODI'], [128, 'Anshu', 'T20'], [84, 'Rahul', 'T20'], [222, 'Kamal','Test'], [244, 'Viswajeet','Test']], columns=['Score', 'Player', 'Matches']) # use mark_bar function to plot a stacked bar and specify x and y axis gp_chart = alt.Chart(data).mark_bar().encode( alt.Column('Matches'), alt.X('Player'), alt.Y('Score', axis=alt.Axis(grid=False)), alt.Color('Player')) # initializer altair_viewer to display the interactive chart alt.renderers.enable('altair_viewer') gp_chart.display() |
Output:
Stacked bar chart
