Python – Matrix elements Frequencies Counter

Sometimes, while working with python Matrix, we can have a problem in which we need to find frequencies of all elements in Matrix. This kind of problem can have application in many domains. Lets discuss certain ways in which this task can be performed.

Method #1 : Using Counter() + sum() + map()
The combination of above methods can be used to perform this task. In this, we perform task of counting elements using Counter() and extending the logic to each row is performed using sum() and map().

# Python3 code to demonstrate
# Matrix elements Frequencies Counter
# using Counter() + sum() + map()
from collections import Counter

# Initializing list
test_list = [[4, 5, 6], [2, 4, 5], [6, 7, 5]]

# printing original list
print("The original list is : " + str(test_list))

# Matrix elements Frequencies Counter
# using Counter() + sum() + map()
res = dict(sum(map(Counter, test_list), Counter()))

# printing result
print ("The frequencies dictionary is : " + str(res))

Output :

The original list is : [[4, 5, 6], [2, 4, 5], [6, 7, 5]]
The frequencies dictionary is : {2: 1, 4: 2, 5: 3, 6: 2, 7: 1}

Method #2 : Using chain() + Counter()
The combination of above functions can be used to perform this task. In this, we flatten the matrix using chain() and compute frequency using Counter().

# Python3 code to demonstrate
# Matrix elements Frequencies Counter
# using Counter() + chain()
from collections import Counter
import itertools

# Initializing list
test_list = [[4, 5, 6], [2, 4, 5], [6, 7, 5]]

# printing original list
print("The original list is : " + str(test_list))

# Matrix elements Frequencies Counter
# using Counter() + chain()
res = dict(Counter(itertools.chain(*test_list)))

# printing result
print ("The frequencies dictionary is : " + str(res))

Output :

The original list is : [[4, 5, 6], [2, 4, 5], [6, 7, 5]]
The frequencies dictionary is : {2: 1, 4: 2, 5: 3, 6: 2, 7: 1}