How to Add Hovering Annotations to Matplotlib Scatter Plots?

How to Create Hovering Annotations in a Plot

When analyzing scatter plots with numerous data points, identifying specific points of interest can be challenging. One convenient solution is to implement hovering annotations that display additional information upon cursor movement.

The matplotlib library provides a versatile functionality for adding annotations to plots. To create hovering annotations, we can utilize the annotate and update_annot functions. The annotate function positions an annotation at a specified coordinate, while update_annot modifies its text and appearance based on the index of the hovered data point.

To achieve hovering annotations, follow these steps:

1. Import the required libraries and generate your data.
2. Create a scatter plot and an invisible annotation object.
3. Define the update_annot function to update the annotation's text and appearance based on the hovered point's index.
4. Implement the hover function to control the annotation's visibility based on cursor movement.
5. Connect the motion_notify_event to the hover function.

By implementing this approach, you can easily add hovering annotations to your scatter plots, providing valuable insights into specific data points without cluttering the plot.

Example:

The provided code snippet demonstrates the implementation of hovering annotations on a scatter plot:

import matplotlib.pyplot as plt
import numpy as np; np.random.seed(1)

x = np.random.rand(15)
y = np.random.rand(15)
names = np.array(list("ABCDEFGHIJKLMNO"))
c = np.random.randint(1,5,size=15)

norm = plt.Normalize(1,4)
cmap = plt.cm.RdYlGn

fig,ax = plt.subplots()
sc = plt.scatter(x,y,c=c, s=100, cmap=cmap, norm=norm)

annot = ax.annotate("", xy=(0,0), xytext=(20,20),textcoords="offset points",
                    bbox=dict(boxstyle="round", fc="w"),
                    arrowprops=dict(arrowstyle="->"))
annot.set_visible(False)

def update_annot(ind):

    pos = sc.get_offsets()[ind["ind"][0]]
    annot.xy = pos
    text = "{}, {}".format(" ".join(list(map(str,ind["ind"]))), 
                           " ".join([names[n] for n in ind["ind"]]))
    annot.set_text(text)
    annot.get_bbox_patch().set_facecolor(cmap(norm(c[ind["ind"][0]])))
    annot.get_bbox_patch().set_alpha(0.4)


def hover(event):
    vis = annot.get_visible()
    if event.inaxes == ax:
        cont, ind = sc.contains(event)
        if cont:
            update_annot(ind)
            annot.set_visible(True)
            fig.canvas.draw_idle()
        else:
            if vis:
                annot.set_visible(False)
                fig.canvas.draw_idle()

fig.canvas.mpl_connect("motion_notify_event", hover)

plt.show()

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