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Counting frequencies of all elements in an array in Python using the collections module

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An unsorted array of n integers is given, which can contain n integers. Count the frequency of all elements present in the 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 different ways, see Counting the frequencies of all elements in the array . In Python, we can quickly fix this problem with the Collections module .

# Function to count the frequency of each element

import collections

 
# returns the dictionary data structure
# 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)

  

  # repeat a dictionary named freq for printing

# number of each item

for key, value in freq.iteritems ():

print key, " -" " , value

Output:

 1 -" 4 2 -" 4 3 -" 2 4 -" 1 5 -" 2 

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