Create Custom Matplotlib Ticker Formatting

Introduction

In this lab, you will learn how to create a custom ticker in Python Matplotlib using the ticker module. The custom ticker will format the y-axis ticks in millions of dollars.

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Import Required Libraries

First, we need to import the required libraries to create the custom ticker. We need the pyplot and ticker modules from Matplotlib.

import matplotlib.pyplot as plt
import matplotlib.ticker as ticker

Define Custom Ticker Function

Next, we need to define the custom ticker function. The custom ticker function takes two arguments - the value and tick position - and returns the formatted tick label. In this case, we will format the tick label as dollars in millions.

def millions(x, pos):
    """The two arguments are the value and tick position."""
    return f'${x*1e-6:1.1f}M'

Create the Plot

Now, we can create the plot with the custom ticker. We will create a bar chart with sample data and set the y-axis ticker to use our custom ticker function.

## Create a bar chart with sample data
fig, ax = plt.subplots()
money = [1.5e5, 2.5e6, 5.5e6, 2.0e7]
ax.bar(['Bill', 'Fred', 'Mary', 'Sue'], money)

## Set the y-axis ticker to use the custom ticker function
ax.yaxis.set_major_formatter(ticker.FuncFormatter(millions))

## Display the plot
plt.show()

Interpret the Output

The output of the code should be a bar chart with the y-axis labels formatted in millions of dollars. The tick labels will be formatted as $0.2M, $2.5M, $5.5M, and $20.0M respectively.

Summary

In this lab, you learned how to create a custom ticker in Python Matplotlib using the ticker module. You also learned how to format the tick labels in millions of dollars using a custom ticker function. This technique can be useful when working with large financial data sets.