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

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

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.



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# 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.iteritems():
        print key, " -> ", value

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Output:

1 -> 4
2 -> 4
3 -> 2
4 -> 1
5 -> 2

Related Article :
Counting the frequencies in a list using dictionary in Python

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