python - How to annotate the values of X and Y while hovering mouse over the bar graph

Question

I have tried to make it but while executing, it shows me the following error:

bar,=plt.bar(xpos,revenue)

ValueError: too many values to unpack

how can i solve it as i want values of x and y in the annotate while hover mouse. This is my following code:

import numpy as np
import matplotlib.pyplot as plt

company=['google','amazon','msft','fb']
revenue=[80,68,54,27]

fig=plt.figure()
ax=plt.subplot()

xpos=np.arange(len(company))

bar,=plt.bar(xpos,revenue)


annot = ax.annotate("", xy=(0,0), xytext=(-20,20),textcoords="offset points",
                    bbox=dict(boxstyle="round", fc="black", ec="b", lw=2),
                    arrowprops=dict(arrowstyle="->"))
annot.set_visible(False)

def update_annot(ind):
    x,y = bar.get_data()
    x0 = x[ind["ind"][0]]
    y0 = y[ind["ind"][0]]
    annot.xy = (x0, y0)
    text = "({:.2g},{:.2g})".format(
        x0,y0,
    )
    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 = bar.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()

Answer 1

The error tells you that plt.bar returns a single object, which cannot be unpacked. So you need to remove the comma (,). Instead call the returned bar container something like bars = plt.bar(xpos,revenue).

You also cannot blindly copy some other solution for scatters or plots for bars. Instead you need to adapt it to the bars. So you need to go through the bars and check which of them, if any, is hovered.

See a complete solution here:

import numpy as np
import matplotlib.pyplot as plt

company=['google','amazon','msft','fb']
revenue=[80,68,54,27]

fig=plt.figure()
ax=plt.subplot()

xpos=np.arange(len(company))

bars = plt.bar(xpos,revenue)


annot = ax.annotate("", xy=(0,0), xytext=(-20,20),textcoords="offset points",
                    bbox=dict(boxstyle="round", fc="black", ec="b", lw=2),
                    arrowprops=dict(arrowstyle="->"))
annot.set_visible(False)

def update_annot(bar):
    x = bar.get_x()+bar.get_width()/2.
    y = bar.get_y()+bar.get_height()
    annot.xy = (x,y)
    text = "({:.2g},{:.2g})".format( x,y )
    annot.set_text(text)
    annot.get_bbox_patch().set_alpha(0.4)


def hover(event):
    vis = annot.get_visible()
    if event.inaxes == ax:
        for bar in bars:
            cont, ind = bar.contains(event)
            if cont:
                update_annot(bar)
                annot.set_visible(True)
                fig.canvas.draw_idle()
                return
    if vis:
        annot.set_visible(False)
        fig.canvas.draw_idle()

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

plt.show()