Pick events for data interaction in Matplotlib

Introduction

Pick events let you click on parts of a plot to get more information or interact with the data.

You want to click on a point in a scatter plot to see its value.

You want to select bars in a bar chart to highlight them.

You want to interact with a plot to filter or update data.

You want to make your plots interactive for presentations.

You want to build simple data exploration tools.

Syntax

Matplotlib

fig.canvas.mpl_connect('pick_event', onpick)

# where onpick is a function that handles the event

The 'pick_event' triggers when you click on a pickable artist (like points or lines).

You must set the 'picker' property on plot elements to make them pickable.

Examples

This makes the line pickable with a 5-point tolerance around it.

Matplotlib

line, = plt.plot(x, y, picker=5)

# picker=5 means the click tolerance in points

Each point in the scatter plot can be clicked to trigger pick events.

Matplotlib

scatter = plt.scatter(x, y, picker=True)

# picker=True makes each point pickable

Sample Program

This code creates a scatter plot where you can click on points. When you click, it prints the point's index and coordinates.

Matplotlib

import matplotlib.pyplot as plt

x = [1, 2, 3, 4, 5]
y = [10, 20, 25, 30, 40]

fig, ax = plt.subplots()
scatter = ax.scatter(x, y, picker=True)

# Define the pick event handler
def onpick(event):
    ind = event.ind[0]  # index of the picked point
    print(f"You clicked on point {ind} with coordinates ({x[ind]}, {y[ind]})")

# Connect the pick event to the handler
fig.canvas.mpl_connect('pick_event', onpick)

plt.title('Click on a point')
plt.show()

Important Notes

Pick events only work if the plot elements have the 'picker' property set.

The event object gives you information about what was clicked, like the index of the point.

Pick events are useful for adding interactivity without complex GUI code.

Summary

Pick events let you click on plot elements to interact with data.

Set 'picker' on plot elements to make them clickable.

Use 'fig.canvas.mpl_connect' to link pick events to your handler function.