How to force plotly select to brush along the x-axis only

FITFLOP

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01-10-2024

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Constraining Plotly Selection: Brushing Only Along the X-Axis

Sometimes, you need to analyze data along a single dimension, focusing solely on the x-axis without allowing selection along the y-axis. This can be useful for analyzing trends over time, comparing data across different groups, or exploring relationships between variables. Plotly's interactive capabilities allow you to achieve this with ease.

Let's imagine you have a scatter plot with data points representing sales across different months. You're interested in analyzing the trends in sales over time, but you don't want the selection area to be influenced by variations in sales values. This is where forcing Plotly select to brush along the x-axis only comes in handy.

Here's an example of how to achieve this:

import plotly.graph_objects as go

# Sample data
months = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
sales = [100, 120, 150, 180, 200, 220, 250, 280, 300, 320, 350, 380]

# Create the scatter plot
fig = go.Figure(data=[go.Scatter(x=months, y=sales, mode='lines+markers')])

# Configure the selection behavior
fig.update_layout(
    dragmode='select',
    selectionrevision=True,
    xaxis_rangemode='normal'  # Ensures the x-axis doesn't autoscale during selection
)

# Define the selection rectangle
fig.update_traces(selector=dict(type='scatter'),
                 selectionmode='x',  # Restrict selection to x-axis
                 selectedpoints=None  # Initial selection is empty
                 )

fig.show()

In this code:

• dragmode='select': This enables the selection mode, allowing you to drag a rectangle to select data points.
• selectionrevision=True: This ensures that the selection updates dynamically as you drag the rectangle.
• xaxis_rangemode='normal': This prevents the x-axis from automatically adjusting its range while selecting.
• selectionmode='x': This is the key to restricting selection to the x-axis.
• selectedpoints=None: This ensures that no points are initially selected.

By implementing these settings, you can effectively focus your analysis on the x-axis, making it easier to understand patterns and trends along that dimension without being influenced by variations in the y-axis.

Additional Notes:

• The selection mode can be further customized using selectionmode='x+y' (default) to allow selection along both axes, or selectionmode='y' to restrict selection to the y-axis.
• Explore the Plotly documentation for a comprehensive understanding of the selectionmode options and other related features.
• The example above focuses on scatter plots, but the same principles apply to other Plotly chart types like line charts, bar charts, and more. You can easily adapt the code to suit your specific visualization needs.

By understanding how to control Plotly selection, you can leverage its interactive capabilities for more focused and insightful data exploration.