Python | Retain records of specific length

• Last Updated : 21 Nov, 2019

Sometimes, while working with records, we might desire to filter records in such a way in which we need to discard records that do not contains exact number of elements required to constitute a record. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using list comprehension + len()
In this method, we just iterate through the list and discard the tuples that do not match the matching length required to constitute the record. The computation of length is done by len().

 # Python3 code to demonstrate working of# Retain records of specific length# Using list comprehension + len()  # Initializing listtest_list = [(4, 5, 6), (5, 6), (2, 3, 5), (5, 6, 8), (5, 9)]  # printing original listprint("The original list is : " + str(test_list))  # Initializing desired length N = 3  # Retain records of specific length# Using list comprehension + len()res =  [sub for sub in test_list if len(sub) == 3]      # printing resultprint("The tuple list after removing uneven records: " + str(res))
Output :
The original list is : [(4, 5, 6), (5, 6), (2, 3, 5), (5, 6, 8), (5, 9)]
The tuple list after removing uneven records: [(4, 5, 6), (2, 3, 5), (5, 6, 8)]

Method #2 : Using filter() + lambda + len()
The combination of above functions can also be used to perform this particular task. In this, we just use filter() and use lambda function to separate uneven length records.

 # Python3 code to demonstrate working of# Retain records of specific length# Using filter() + lambda + len()  # Initializing listtest_list = [(4, 5, 6), (5, 6), (2, 3, 5), (5, 6, 8), (5, 9)]  # printing original listprint("The original list is : " + str(test_list))  # Initializing desired length N = 3  # Retain records of specific length# Using filter() + lambda + len()res = list(filter(lambda ele: len(ele) == N, test_list))      # printing resultprint("The tuple list after removing uneven records: " + str(res))
Output :
The original list is : [(4, 5, 6), (5, 6), (2, 3, 5), (5, 6, 8), (5, 9)]
The tuple list after removing uneven records: [(4, 5, 6), (2, 3, 5), (5, 6, 8)]

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