How can I draw histogram for array in Python?

Note that matplotlib's hist does not play nicely with string data (see the bar/tick positions):

import matplotlib.pyplot as plt

plt.hist(arr)

It's certainly possible to fix this manually, but it's easier to use pandas or seaborn. Both use matplotlib under the hood, but they provide better default formatting.

Also:

• If there are too many bars to fit comfortably in the default frame, you can widen the figsize. In these examples I've set figsize=(6, 3).
• If you want to rotate the x ticks, add plt.xticks(rotation=90).

pandas

• pandas value_counts and plot.bar

  import pandas as pd
  
  pd.value_counts(arr).plot.bar(figsize=(6, 3))
  # pd.Series(arr).value_counts().plot.bar(figsize=(6, 3))
  

  

seaborn

• seaborn histplot

  import seaborn as sns
  import matplotlib.pyplot as plt
  
  fig, ax = plt.subplots(figsize=(6, 3))
  sns.histplot(arr, ax=ax)
  

  

• seaborn countplot

  import seaborn as sns
  import matplotlib.pyplot as plt
  
  fig, ax = plt.subplots(figsize=(6, 3))
  sns.countplot(arr, ax=ax)
  

  

matplotlib

• collections.Counter with matplotlib bar

  from collections import Counter
  
  counts = Counter(arr)
  fig, ax = plt.subplots(figsize=(6, 3))
  ax.bar(counts.keys(), counts.values())
  

  

• numpy unique with matplotlib bar

  import numpy as np
  
  uniques, counts = np.unique(arr, return_counts=True)
  fig, ax = plt.subplots(figsize=(6, 3))
  ax.bar(uniques, counts)
  

  

You can use the matplotlib library to plot a histogram directly from a list. The code for it goes as follows:

from matplotlib import pyplot as plt

arr= ['a','a','a','b','c','b']

plt.hist(arr)
plt.show()

You can check out more about the histogram function from matplotlib out here: https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.hist.html

You can do other stuff like setting the color for your histogram plot, changing the alignment, and many other things.

Histograms are used for numerical data. Your strings data (categorical) it would be better to use a bar chart. Here's the code to generate a bar chart with matplotlib:

import matplotlib.pyplot as plt
from collections import Counter
arr= ['a', 'a', 'a', 'b', 'c', 'b']
data = Counter(arr)
plt.bar(data.keys(), data.values())
plt.show()

Even though histogram and bar chart in this case look similar, with an histogram you could have an unexpected result for instance if requiring a certain number of bins.

There are multiple steps to this problem..

Step 1: You need to collect the data in a convenient location. Going by your example, a good option would be to make a list with values. This could use a .count() to accomplish that. Other methods are possible, of course.

Step 2: To display the data, you could use a lib like matplotlib.pyplot. This may also take care of step 1. But that is not importent.