Mastering Matplotlib: Tips for Customizing your Plots and Line Charts

Data visualization is an essential skill for anyone who works with data. Being able to effectively present your data can help you identify trends, communicate insights, and make more informed decisions.

Matplotlib is a popular library for creating plots and charts in Python. In this article, we will cover two essential skills that will help you customize your plots and line charts in Matplotlib: changing the order of legend items and creating line charts.

## Changing the Order of Legend Items in Matplotlib

When creating visualizations, you may want to reorder the legend items to communicate specific information effectively. For instance, if you are plotting a line chart with multiple lines, you may want to control the order of the legend items to communicate which line corresponds to which variable.

Matplotlib makes it easy to customize the order of the legend items using handles and labels. To change the order of legend items in Matplotlib, follow these steps:

Step 1: Create a line chart with multiple lines using plt.plot()

x = [1, 2, 3, 4, 5, 6]

y1 = [4, 8, 3, 6, 7, 9]

y2 = [2, 6, 1, 3, 5, 8]

y3 = [1, 5, 7, 4, 3, 2]

plt.plot(x, y1, label=’Line 1′)

plt.plot(x, y2, label=’Line 2′)

plt.plot(x, y3, label=’Line 3′)

Step 2: Retrieve the handles and labels using get_legend_handles_labels()

handles, labels = plt.gca().get_legend_handles_labels()

Step 3: Use the handles and labels to generate the legend using plt.legend()

plt.legend(handles, labels, loc=’best’)

By default, Matplotlib encodes the legend items in the order they were plotted.

However, you can change the order of the handles and labels to customize the legend items’ order. For instance, you can change the order of the handles and labels to order the legend items based on their median values.

To order the legend items based on their median values, follow these steps:

Step 1: Create a dictionary that maps the labels to their median values.

median_values = {‘Line 1’: np.median(y1), ‘Line 2’: np.median(y2), ‘Line 3’: np.median(y3)}

Step 2: Sort the labels based on their median values using sorted()

sorted_labels = sorted(labels, key=lambda x: median_values[x], reverse=True)

Step 3: Sort the handles based on their corresponding labels.

sorted_handles = [handles[labels.index(label)] for label in sorted_labels]

Step 4: Generate the legend using the updated handles and labels. plt.legend(sorted_handles, sorted_labels)

## Creating a Line Chart in Matplotlib

Line charts are a popular data visualization technique that allows you to display trends over time. Matplotlib makes it easy to create a line chart in just a few lines of code.

Here’s an example of how to create a line chart with data in Matplotlib:

Step 1: Import the necessary libraries

## import pandas as pd

import matplotlib.pyplot as plt

Step 2: Load your data into a Pandas dataframe

data = pd.read_csv(‘data.csv’)

Step 3: Create a line chart using plt.plot()

plt.plot(data[‘Year’], data[‘Value’])

Step 4: Customize various aspects of the line chart, such as the xlabel, ylabel, and title. plt.xlabel(‘Year’)

plt.ylabel(‘Value’)

plt.title(‘Value Over Time’)

Step 5: Display the line chart using plt.show()

plt.show()

## Adding a Legend to the Line Chart

Adding a legend to the line chart can help your audience understand the data better. The legend identifies the different lines in the line chart and maps them to specific variables.

Here’s how to add a legend to your line chart in Matplotlib:

Step 1: Add a label argument to each call to plt.plot()

plt.plot(data[‘Year’], data[‘Value’], label=’Value’)

Step 2: Generate the legend using plt.legend()

plt.legend(loc=’best’)

Step 3: Display the line chart using plt.show()

plt.show()

## Conclusion

Matplotlib is a powerful library that can help you create highly customizable visualizations. In this article, we covered two essential skills for customizing your plots and line charts in Matplotlib: changing the order of legend items and creating line charts.

By mastering these techniques, you can create professional-looking visualizations that help you communicate your data effectively.

## 3) Combining Syntax and Example for Legend Order Customization in a Line Chart

Matplotlib provides a straightforward way of customizing the order of legend items. Suppose we want to change the order of the legend items in the example we used for creating a line chart.

In that case, we can use the syntax we presented earlier to customize the legend elements’ order. Let’s consider an example.

## Suppose we have created a line chart that shows the stock prices of three different companies from 2010 to 2020 as follows:

“`

## import pandas as pd

import matplotlib.pyplot as plt

data = pd.read_csv(‘stocks.csv’)

plt.plot(data[‘Year’], data[‘AAPL’], label=’Apple’)

plt.plot(data[‘Year’], data[‘GOOG’], label=’Google’)

plt.plot(data[‘Year’], data[‘MSFT’], label=’Microsoft’)

plt.xlabel(‘Year’)

plt.ylabel(‘Price($)’)

plt.title(‘Stock Prices of Apple, Google, and Microsoft from 2010 to 2020’)

plt.legend()

plt.show()

“`

This code creates a line chart of the stock prices of Apple, Google, and Microsoft from 2010 to 2020. The legend generated by Matplotlib orders the items based on the lines’ color.

To customize the order of the legend items, we can use the syntax we presented earlier. “`

## import numpy as np

handles, labels = plt.gca().get_legend_handles_labels()

median_values = {‘Apple’: np.median(data[‘AAPL’]),

‘Google’: np.median(data[‘GOOG’]),

‘Microsoft’: np.median(data[‘MSFT’])}

sorted_labels = sorted(labels, key=lambda x: median_values[x], reverse=True)

sorted_handles = [handles[labels.index(label)] for label in sorted_labels]

plt.legend(sorted_handles, sorted_labels)

“`

Here, we retrieve the handles and labels of the plot using `plt.gca().get_legend_handles_labels()`. We then calculate the median value for each line and create a dictionary mapping the labels to their median values.

Next, we sort the labels based on their corresponding median values using `sorted()`, passing the `key` function as a lambda function that retrieves the value of the corresponding median from the `median_values` dictionary. Lastly, we sort the handles based on their corresponding labels using a list comprehension.

We use the new lists to generate the reordered legend. This syntax helps us order the legend items based on specific criteria, such as the median value of the plotted data.

By following this syntax, we can create clear and concise visualizations that communicate our data’s insights more effectively.

## 4) Overall

In this article, we covered two essential skills for customizing line charts in Matplotlib: changing the order of legend items and adding legends to our plotted charts. We presented the syntax and examples for both of these skills.

By changing the order of legend items, we can communicate specific information effectively and ensure that our audiences can better understand our visualizations. We can customize the legend order in Matplotlib by using handles and labels.

Additionally, we discussed how to create a line chart in Matplotlib and add legends to our plotted charts. Legends help identify the different lines in our plots, thereby mapping them to specific variables and helping our audiences understand the data better.

By mastering these skills, one can create professional-looking visualizations that help communicate data insights effectively. Matplotlib is a powerful tool that allows users to create highly customizable visualizations, enabling the creation of impactful data stories.

In summary, this article discussed the essential skills required for customizing line charts in Matplotlib, including changing the order of legend items and adding legends to plotted charts. To change the order of legend items in Matplotlib, we can use handles and labels to customize legend elements’ order.

Adding a legend to our line chart helps identify the different variables, thereby making it easier for our audiences to understand the data better. By mastering these skills, users can create professional-looking visualizations that communicate data insights effectively.

The Matplotlib library offers a powerful set of tools for visualizing and presenting data, making it an essential skill set for those who work with data.