Python | Extract least frequency element

Sometimes, while working with data, we can have a problem in which we need to extract element which is occurring least number of times in the list. Let’s discuss certain ways in which this problem can be solved.

Method #1 : Using defaultdict() + loop
The combination of above functions can be used to perform this task. In this, we extract each element’s frequency using defaultdict() and extract the minimum frequency element after traversing the defaultdict.

# Python3 code to demonstrate working of 
# Extract least frequency element 
# using defaultdict() + loop 
from collections import defaultdict 
  
# initialize list  
test_list = [1, 3, 4, 5, 1, 3, 5] 
  
# printing original list  
print("The original list : " + str(test_list)) 
  
# Extract least frequency element 
# using defaultdict() + loop 
res = defaultdict(int) 
for ele in test_list: 
   res[ele] += 1 
min_occ = 9999
for ele in res: 
    if min_occ > res[ele]: 
        min_occ = res[ele] 
        tar_ele = ele 
  
# printing result 
print("The minimum occurring element is : " + str(tar_ele)) 

Output :

The original list : [1, 3, 4, 5, 1, 3, 5]
The minimum occurring element is : 4

Method #2 : Using Counter()
This method is similar to above, the difference is that the frequency is stored using Counter() and then we extract element with least frequency.

# Python3 code to demonstrate working of 
# Extract least frequency element 
# using Counter() 
from collections import Counter 
  
# initialize list  
test_list = [1, 3, 4, 5, 1, 3, 5] 
  
# printing original list  
print("The original list : " + str(test_list)) 
  
# Extract least frequency element 
# using Counter 
res = Counter(test_list) 
tar_ele = res.most_common()[-1][0] 
  
# printing result 
print("The minimum occurring element is : " + str(tar_ele)) 

Output :

The original list : [1, 3, 4, 5, 1, 3, 5]
The minimum occurring element is : 4

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