Understanding the Error in Plotting a Boxplot with Pandas and Matplotlib

Introduction

Boxplots are an effective way to visualize the distribution of a dataset. In this article, we’ll explore how to plot a boxplot using pandas and matplotlib, addressing a specific error encountered while doing so.

Background on Boxplots

A boxplot is a graphical representation that displays the distribution of data based on its quartiles and outliers. It’s often used in statistics to compare the distribution of multiple datasets. The general structure of a boxplot includes:

• Quartiles: Divided into four parts: Q1 (first quartile), median (Q2), and Q3.
• Outliers: Data points that are significantly different from the other data points.

Understanding Pandas’ Boxplot Functionality

Pandas provides a convenient function to plot boxplots, which can be found in the pandas.DataFrame.boxplot() method. However, it seems like this function has undergone changes between versions of pandas and matplotlib, leading to the unexpected behavior encountered in the given question.

Exploring the Code Snippet Provided

The provided code snippet contains two attempts at creating a boxplot using the loans.boxplot() method:

# Attempt 1
loans.boxplot(columns="RevolvingUtilizationOfUnsecuredLines")

# Attempt 2
loans.boxplot(column="RevolvingUtilizationOfUnsecuredLines")

The first attempt raises a TypeError with the message “boxplot() got an unexpected keyword argument ‘columns’”. The second attempt produces a KeyError.

Understanding the Correct Usage of Pandas’ Boxplot Functionality

After reviewing the pandas documentation, it becomes clear that the correct usage for plotting a boxplot using pandas and matplotlib involves specifying only one parameter: the column to plot.

# Correct code snippet:
loans.boxplot(column="RevolvingUtilizationOfUnsecuredLines")

Note how columns has been replaced with column. This change may have resulted from changes in pandas or matplotlib versions, leading to the unexpected behavior encountered in the given question.

How the Error Occurred

The initial mistake lies in misunderstanding the keyword arguments accepted by the loans.boxplot() function. When attempting to plot a boxplot for the specified column using columns="RevolvingUtilizationOfUnsecuredLines", pandas threw an error indicating that boxplot() got an unexpected keyword argument ‘columns’. This likely stems from changes in how pandas and matplotlib integrate their functionalities.

Additional Code and Advice

For additional assistance, refer to this code snippet:

import pandas as pd
import matplotlib.pyplot as plt

# Sample dataframe for demonstration purposes:
data = {
    "Sr_No": [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
    "SeriousDlqin2yrs": [1, 0, 0, 0, 1, 0, 0, 0, 0, 0],
    "RevolvingUtilizationOfUnsecuredLines": [0.766126609, 0.957151019, 0.65818014, 0.233809776,
                                             0.9072394, 0.213178682, 0.305682465, 0.754463648, 0.116950644, 0.189169052],
    "age": [45, 40, 38, 30, 49, 74, 57, 39, 27, 57],
    "NumberOfTime30-59DaysPastDueNotWorse": [2, 0, 1, 0, 1, 0, 0, 0, 0, 0],
    # Additional columns omitted for brevity
}

# Sample dataframe creation:
loans = pd.DataFrame(data)

# Boxplot example using pandas.boxplot():
loans.boxplot(column="RevolvingUtilizationOfUnsecuredLines")

plt.show()

Conclusion

Plotting a boxplot can be challenging, especially when encountering unexpected errors. By understanding how to use pandas and matplotlib effectively, you’ll find creating data visualizations easier. In the case of plotting a boxplot using pandas and matplotlib, make sure that you specify only one column name for plotting purposes.

When facing issues, consult the documentation for both libraries thoroughly. Sometimes understanding changes made by library developers may require more investigation to resolve.

Last modified on 2023-07-02