Brtdku

I am using matplotlib to make scatter plots. Each point on the scatter plot is associated with a named object. I would like to be able to see the name of an object when I hover my cursor over the point on the scatter plot associated with that object. In particular, it would be nice to be able to quickly see the names of the points that are outliers. The closest thing I have been able to find while searching here is the annotate command, but that appears to create a fixed label on the plot. Unfortunately, with the number of points that I have, the scatter plot would be unreadable if I labeled each point. Does anyone know of a way to create labels that only appear when the cursor hovers in the vicinity of that point?

It seems none of the other answers here actually answer the question. So here is a code that uses a scatter and shows an annotation upon hovering over the scatter points.

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()

Because people suddenly also want to use this solution for a line plot instead of a scatter, the following would be the same solution for plot (which works slightly differently).

import matplotlib.pyplot as plt

import numpy as np; np.random.seed(1)



x = np.sort(np.random.rand(15))

y = np.sort(np.random.rand(15))

names = np.array(list("ABCDEFGHIJKLMNO"))



norm = plt.Normalize(1,4)

cmap = plt.cm.RdYlGn



fig,ax = plt.subplots()

line, = plt.plot(x,y, marker="o")



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):

    x,y = line.get_data()

    annot.xy = (x[ind["ind"][0]], y[ind["ind"][0]])

    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_alpha(0.4)





def hover(event):

    vis = annot.get_visible()

    if event.inaxes == ax:

        cont, ind = line.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()

In case someone is looking for a solution for bar plots, please refer to e.g. this answer.

I know it's an old question, but I kept on arriving here while looking for a solution to hover (not click on) a line.

import matplotlib.pyplot as plt



fig = plt.figure()

plot = fig.add_subplot(111)



# create some curves

for i in range(4):

    plot.plot(

        [i*1,i*2,i*3,i*4],

        gid=i)



def on_plot_hover(event):

    for curve in plot.get_lines():

        if curve.contains(event)[0]:

            print "over %s" % curve.get_gid()



fig.canvas.mpl_connect('motion_notify_event', on_plot_hover)           

plt.show()

From http://matplotlib.sourceforge.net/examples/event_handling/pick_event_demo.html :

from matplotlib.pyplot import figure, show

import numpy as npy

from numpy.random import rand





if 1: # picking on a scatter plot (matplotlib.collections.RegularPolyCollection)



    x, y, c, s = rand(4, 100)

    def onpick3(event):

        ind = event.ind

        print 'onpick3 scatter:', ind, npy.take(x, ind), npy.take(y, ind)



    fig = figure()

    ax1 = fig.add_subplot(111)

    col = ax1.scatter(x, y, 100*s, c, picker=True)

    #fig.savefig('pscoll.eps')

    fig.canvas.mpl_connect('pick_event', onpick3)



show()

• This recipe draws an annotation on picking a data point: http://scipy-cookbook.readthedocs.io/items/Matplotlib_Interactive_Plotting.html .


• This recipe draws a tooltip, but it requires wxPython:
  Point and line tooltips in matplotlib?