 Open in App
Not now

# Count frequencies of all elements in array in Python using collections module

• Difficulty Level : Easy
• Last Updated : 22 Feb, 2023

Given an unsorted array of n integers which can contains n integers. Count frequency of all elements that are present in array. Examples:

```Input : arr[] = [1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 4, 5, 5]
Output : 1 -> 4
2 -> 4
3 -> 2
4 -> 1
5 -> 2```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

This problem can be solved in many ways, refer Count frequencies of all elements in array link. In Python, we can quickly solve this problem in using Collections module.

Implementation:

## Python

 `# Function to count frequency of each element``import` `collections` `# it returns a dictionary data structure whose``# keys are array elements and values are their``# corresponding frequencies {1: 4, 2: 4, 3: 2,``# 5: 2, 4: 1}``def` `CountFrequency(arr):``    ``return` `collections.Counter(arr)` `# Driver function``if` `__name__ ``=``=` `"__main__"``:` `    ``arr ``=` `[``1``, ``1``, ``1``, ``1``, ``2``, ``2``, ``2``, ``2``, ``3``, ``3``, ``4``, ``5``, ``5``]``    ``freq ``=` `CountFrequency(arr)` `    ``# iterate dictionary named as freq to print``    ``# count of each element``    ``for` `(key, value) ``in` `freq.items():``        ``print` `(key, ``" -> "``, value)`

Output

```(1, ' -> ', 4)
(2, ' -> ', 4)
(3, ' -> ', 2)
(4, ' -> ', 1)
(5, ' -> ', 2)```

The time complexity of this function is O(n), where n is the length of the input array.

The auxiliary space required by this function is O(k), where k is the number of unique elements in the input array.