Add error bars to a Matplotlib bar plot

In this article, we will create a bar plot with error bars using Matplotlib. Error bar charts are a great way to represent the variability in your data. It can be applied to graphs to provide an additional layer of detailed information on the presented data.

Approach:

• Import the required Python library
• Making simple data
• Plot using the plt.errorbar() function
• Display graph

The errorbar() function in the pyplot module of the matplotlib library plots data points of y versus x with optional error bars, either as lines, markers, or both.

Syntax for the Function

matplotlib.pyplot.errorbar(
x, y,
yerr=None, xerr=None,
fmt='',
ecolor=None, elinewidth=None, capsize=None,
barsabove=False, lolims=False, uplims=False,
xlolims=False, xuplims=False, errorevery=1,
capthick=None,
*, data=None,
**kwargs
)

Description of Parameters

• x, y: Horizontal and vertical coordinates of the data points (required).
• yerr, xerr: Errors for the y and x coordinates, can be a single value or an array.
• fmt: Format for the markers (e.g. 'o', 's', 'b-'). Default is ''.
• ecolor: Color of the error bars. Default is None (uses the current axis color).
• elinewidth: Line width of error bars. Default is None (default line width).
• capsize: Length of the caps at the ends of the error bars. Default is None.
• barsabove: If True, error bars are drawn above the plot symbols. Default is False.
• lolims, uplims, xlolims, xuplims: Limit error bars to certain regions. Default is False for all.
• errorevery: Frequency of error bars (default is 1, for all points).
• capthick: Thickness of the cap lines. Default is None.
• data: Data object (e.g. pandas DataFrame) to use.
• kwargs: Additional keyword arguments for customizing properties.

Implementing Error bars in Python

Example 1:  Adding some errors in a 'y' value

import matplotlib.pyplot as plt

x = [1, 3, 5, 7]
y = [11, 2, 4, 19]

c = [1, 3, 2, 1]

plt.bar(x, y)
plt.errorbar(x, y, yerr=c, fmt="o", color="r")
plt.show()

Output:

Example 2:  Adding Some errors in the 'x' value

import matplotlib.pyplot as plt

x = [1, 3, 5, 7]
y = [11, 2, 4, 19]

c = [1, 3, 2, 1]

plt.bar(x, y)
plt.errorbar(x, y, xerr=c, fmt="o", color="r")
plt.show()

Output:

Example 3: Adding error in x and y

import matplotlib.pyplot as plt

x = [1, 3, 5, 7]
y = [11, 2, 4, 19]

c = [1, 3, 2, 1]
d = [1, 3, 2, 1]

plt.bar(x, y)
plt.errorbar(x, y, xerr=c, yerr=d, fmt="o", color="r")
plt.show()

Output:

Example 4: Adding variable error in x and y

import matplotlib.pyplot as plt

x = [1, 2, 3, 4, 5]
y = [1, 2, 1, 2, 1]

y_errormin = [0.1, 0.5, 0.9, 0.1, 0.9]
y_errormax = [0.2, 0.4, 0.6,  0.4, 0.2]

x_error = 0.5

y_error = [y_errormin, y_errormax]

plt.bar(x, y)
plt.errorbar(x, y, yerr=y_error,
             xerr=x_error, fmt='o', color="r")
plt.show()

Output: