Histograms with Matplotlib

Topics Covered

1. What is a Histogram?
2. Syntax of hist function in Matplotlib
3. Plot a simple histogram in Matplotlib
4. Plotting multiple datasets with different color in a histogram
   

What is a Histogram?

A histogram is a bar chart showing the frequency distribution of numerical data.

However, it is different from a bar chart. A histogram is used for continuous data, where the bins represent different ranges of data. A bar chart on the other hand, represents categorical variables.

You can use the hist() function to plot histograms in Matplotlib.

Syntax of hist function in Matplotlib

matplotlib.pyplot.hist(x, bins=None, range=None, density=False, weights=None, cumulative=False, bottom=None, histtype=’bar’, align=’mid’, orientation=’vertical’, rwidth=None)

Parameters

• x - Input values that can be a single array or a sequence of arrays.
• bins - Range of values which can be either integer or sequence, default is 10.
• range - The lower and upper range of the bins.
• weights - This parameter denotes the weight of each value.
• cumulative - The count of each bin together with the count of the bin for previous values.
• bottom - It denotes location of baseline of each bin.
• histtype - It denotes the type of histogram to be plotted - bar,bar stacked,step or step filled.
• align - Alignment position of the histogram - left, right or middle(default).
• orientation - It denotes whether you want to plot your histogram horizontally or vertically(default).
• rwidth - It denotes the relative width of the bars with respect to bin width.

Plot a simple histogram in Matplotlib

Let's build a histogram of basic distribution. You can use the random function from NumPy for the distribution.

import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
 
# Using numpy random function to generate random data
np.random.seed(19685689)
 
mu, sigma = 100, 20
x = mu + sigma * np.random.randn(10000)
 
# passing the histogram function
n, bins, patches = plt.hist(x, 50, histtype='bar', density=True)
 
 
plt.xlabel('Values')
plt.ylabel('Probability Distribution')
plt.title('Simple histogram with Matplotlib')
plt.xlim(40, 180)
plt.ylim(0, 0.04)
plt.grid(True)
plt.show()

Plotting multiple datasets with different color in a histogram

If you are trying to plot multiple datasets in a histogram, you can differentiate each dataset with a different color.

import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
 
# Using numpy random function to generate random data
np.random.seed(19685689)
 
x = np.random.randn(500000, 3)
colors = ['blue', 'black', 'red']

# passing the histogram function
n, bins, patches = plt.hist(x, 50, histtype='bar', density=True, color=colors)

plt.title('Simple histogram with Matplotlib')
plt.grid(True)
plt.show()

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