How to Change Subplot Titles After Creation in Plotly

When creating visualizations with Plotly, especially with subplots, you might need to modify the titles after the initial plot creation. Whether you forgot to add titles initially or simply want to adjust them later, Plotly provides flexible methods to make these changes. In this article, we will explore how to change subplot titles after the creation of a plot in Plotly.

Understanding Subplots in Plotly

Subplots are a powerful feature in Plotly that allow you to display multiple plots within a single figure. This is particularly useful when you want to compare different datasets or variables side by side. In Plotly, subplots can be created using the make_subplots function from the plotly.subplots module.

Before we dive into changing titles after creation, let's quickly review how to create subplots with titles.

import plotly.graph_objs as go
from plotly.subplots import make_subplots

# Create a subplot figure with 1 row and 2 columns
fig = make_subplots(rows=1, cols=2, subplot_titles=("Plot 1", "Plot 2"))

# Add traces to the subplots
fig.add_trace(go.Scatter(x=[1, 2, 3], y=[4, 5, 6]), row=1, col=1)
fig.add_trace(go.Bar(x=[1, 2, 3], y=[6, 5, 4]), row=1, col=2)

# Display the figure
fig.show()

Output:

In the code above, we create a figure with two subplots and assign titles "Plot 1" and "Plot 2" to the first and second subplots, respectively.

Changing Subplot Titles After Creation

Sometimes, you might need to change the subplot titles after the figure has already been created. This can be done by directly modifying the layout of the figure. To change subplot titles after the plot has been created, we need to access and modify the annotations within the figure's layout. Plotly stores subplot titles as annotations, which can be accessed and modified directly. Step-by-Step Guide:

1. Access Annotations: Subplot titles are stored as annotations in the layout.annotations list of the figure object.
2. Modify Titles: Iterate over the annotations and update the text property to change the titles.
3. Update the Figure: Once the titles are updated, the figure will reflect these changes when displayed.

Method 1: By Modifying layout.annotations

Each subplot title in a Plotly figure is stored as an annotation in the figure's layout. To change a title, you can directly modify the corresponding annotation.

# Modify the first subplot title
fig.layout.annotations[0].text = "Updated Plot 1"

# Modify the second subplot title
fig.layout.annotations[1].text = "Updated Plot 2"

# Display the updated figure
fig.show()

Output:

In this example, the titles of the first and second subplots are updated to "Updated Plot 1" and "Updated Plot 2", respectively.

Method 2: Using Loop for Updating Titles

If you have many subplots, it might be more efficient to update the titles using a loop.

# New titles for the subplots
new_titles = ["New Plot 1", "New Plot 2"]

# Loop through the annotations and update the titles
for i, new_title in enumerate(new_titles):
    fig.layout.annotations[i].text = new_title

# Display the updated figure
fig.show()

Output:

This method is particularly useful when you have a large number of subplots and want to programmatically update their titles.

3. Updating Title Properties

In addition to changing the text of the subplot titles, you can also customize other aspects such as font size, color, and alignment.

# Update title properties
fig.layout.annotations[0].update(text="Custom Plot 1", font=dict(size=16, color="blue"), align="center")
fig.layout.annotations[1].update(text="Custom Plot 2", font=dict(size=14, color="green"), align="left")

# Display the updated figure
fig.show()

Output:

In this code snippet, we change the font size and color of the subplot titles, as well as their alignment. This allows for a more personalized and visually appealing presentation of your data.

Best Practices and Considerations

• Performance: Updating annotations can be computationally expensive for large figures. Limit the frequency of updates in interactive applications.
• Consistency: Ensure that the number of annotations matches the number of subplots to avoid index errors.
• Accessibility: Use descriptive titles to enhance the interpretability of your plots.

Conclusion

Changing subplot titles after creation in Plotly is straightforward and flexible. By directly modifying the layout.annotations property, you can easily update the titles and further customize their appearance. Whether you need to update a single title or multiple titles programmatically, Plotly's powerful capabilities make it easy to achieve the desired result.