How to add error bars to a grouped bar plot?

Question

I would like to add error bar in my plot that I can show the min max of each plot. Please, anyone can help me. Thanks in advance.

The min max is as follow:

Delay =

Answer 1

• In order to plot in the correct location on a bar plot, the patch data for each bar must be extracted.
• An ndarray is returned with one matplotlib.axes.Axes per column.
  • In the case of this figure, ax.patches contains 8 matplotlib.patches.Rectangle objects, one for each segment of each bar.
    • By using the associated methods for this object, the height, width, and x locations can be extracted, and used to draw a line with plt.vlines.
• The height of the bar is used to extract the correct min and max value from dict, z.
  • Unfortunately, the patch data does not contain the bar label (e.g. Delay & Latency).

import pandas as pd
import matplotlib.pyplot as plt

# create dataframe
Delay = (53.46, 36.22, 83, 17)
Latency = (38, 44, 53, 10)
index = ['T=0', 'T=26', 'T=50','T=900']
df = pd.DataFrame({'Delay': Delay, 'Latency': Latency}, index=index)

# dicts with errors
Delay_error = {53.46: {'min': 0,'max': 60}, 36.22: {'min': 12,'max': 70}, 83: {'min': 21,'max': 54}, 17: {'min': 12,'max': 70}}
Latency_error = {38: {'min': 2, 'max': 70}, 44: {'min': 12,'max': 87}, 53: {'min': 9,'max': 60}, 10: {'min': 11,'max': 77}}

# combine them; providing all the keys are unique
z = {**Delay_error, **Latency_error}

# plot
ax = df.plot.bar(rot=0)
plt.xlabel('Time')
plt.ylabel('(%)')
plt.ylim(0, 101)

for p in ax.patches:
    x = p.get_x()  # get the bottom left x corner of the bar
    w = p.get_width()  # get width of bar
    h = p.get_height()  # get height of bar
    min_y = z[h]['min']  # use h to get min from dict z
    max_y = z[h]['max']  # use h to get max from dict z
    plt.vlines(x+w/2, min_y, max_y, color='k')  # draw a vertical line

• If there are non-unique values in the two dicts, so they can't be combined, we can select the correct dict based on the bar plot order.
• All the bars for a single label are plotted first.
  • In this case, index 0-3 are the Dalay bars, and 4-7 are the Latency bars

for i, p in enumerate(ax.patches):
    print(i, p)
    x = p.get_x()
    w = p.get_width()
    h = p.get_height()
    
    if i < len(ax.patches)/2:  # select which dictionary to use
        d = Delay_error
    else:
        d = Latency_error
        
    min_y = d[h]['min']
    max_y = d[h]['max']
    plt.vlines(x+w/2, min_y, max_y, color='k')