CODEWITHSUNDEEP
pythonpython-3.x
user12217822
user12217822

Reputation: 302

How to draw histogram for array in python?

I have an array that has different values, some of which are duplicates. How can I draw a histogram for them whose horizontal axis is the name of the element and the vertical axis is the number in the array?

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

Upvotes: 1

Views: 3032

Answers (4)

user2314737
user2314737

Reputation: 29407

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()

barchart

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.

Upvotes: 0

tdy
tdy

Reputation: 41437

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)

Upvotes: 1

user11931195
user11931195

Reputation:

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.

If your use case is defferent. Please provide more details so that we can help you better

Upvotes: 0

Suraj S Jain
Suraj S Jain

Reputation: 535

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.

Cheers!

Upvotes: 1

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