Python - How To Count Unique Values in Python List

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This article will introduce different methods to count unique values inside list. using the following methods:

• `collections.Counter`
• `set(listName)`
• `np.unique(listName)`

Use `collections.counter` to Count Unique Values in Python List

`collections` is a Python standard library, and it contains the `Counter` class to count the hashable objects.

`Counter` class has two methods :

1. `keys()` returns the unique values in the list.
2. `values()` returns the count of every unique value in the list.

We can use the `len()` function to get the number of unique values by passing the `Counter` class as the argument.

Example Codes:

``from collections import Counter  words = ['Z', 'V', 'A', 'Z','V']  print(Counter(words).keys()) print(Counter(words).values())  print(Counter(words)) ``

Output:

``['V', 'A', 'Z'] [2, 1, 2] 3 ``

Use `set` to Count Unique Values in Python List

`set` is an unordered collection data type that is iterable, mutable, and has no duplicate elements. We can get the length of the `set` to count unique values in the list after we convert the list to a `set` using the `set()` function.

Example Codes:

``words = ['Z', 'V', 'A', 'Z','V'] print(len(set(words))) ``

Output:

``3 ``

Use `numpy.unique` to Count the Unique Values in Python List

returns the unique values of the input array-like data, and also returns the count of each unique value if the `return_counts` parameter is set to be `True`.

Example Codes:

``import numpy as np  words = ['Z', 'V', 'A', 'Z','V']  np.unique(words)  print(len(np.unique(words))) ``

Output:

``3 ``