Python Program to Delete All Odd Frequency Elements from an Array/List
In the previous article, we have discussed Python Program to Remove Even Frequency Characters from the String
Given a list and the task is to delete all the elements from a given list that has an odd frequency.
Examples:
Example1:
Input:
Given List = [10, 4, 2, 10, 1, 2, 3, 4, 5, 6, 6]
Output:
The list after deletion of all the elements from a given list that has an odd frequency : [10, 4, 2, 10, 2, 4, 6, 6]
Example2:
Input:
Given List = [1, 6, 8, 2, 1, 7, 6, 8]
Output:
The list after deletion of all the elements from a given list that has an odd frequency : [1, 6, 8, 1, 6, 8]
Program to Delete All Odd Frequency Elements from an Array/List in Python
Below are the ways to delete all the elements from a given list that has an odd frequency:
- Using Dictionary (Hashing, User Input)
- Using Counter() function (Hashing, Static Input)
- Using Counter() function (Hashing, User Input)
- Using Counter() function (Hashing, User Input)
Method #1: Using Dictionary (Hashing, Static Input)
Approach:
- Take a dictionary and initialize it to empty using the {} or dict() say freqncyDictionary.
- Give the list as static input and store it in a variable.
- Loop in the given list using the For loop.
- Inside the For loop, Check if the list element is present in the dictionary or not using the if conditional statement and ‘in‘ keyword.
- If it is true then increment the count of the list element in the dictionary by 1.
- Else initialize the dictionary with the list element as key and value as 1.
- Take a new empty list say modifdlst and store it in a variable.
- Loop in the given list using the For loop.
- Check if the key in the freqncyDictionary having value even using the if conditional statement.
- If it is true then append the key value to the above declared empty list modifdlst.
- Print the list after deletion of all the elements from a given list that has an odd frequency.
- The Exit of the Program.
Below is the implementation:
# Take a dictionary and initialize it to empty
# using the {} or dict() say freqncyDictionary.
freqncyDictionary = {}
# Give the list as static input and store it in a variable.
gvnlst = [10, 4, 2, 10, 1, 2, 3, 4, 5, 6, 6]
# Loop in the given list using the For loop.
for i in gvnlst:
# Inside the For loop,
# Check if the list element is present in the dictionary
# or not using the if conditional statement and 'in' keyword.
if i in freqncyDictionary.keys():
# If it is true then increment the count of the list element
# in the dictionary by 1.
freqncyDictionary[i] = freqncyDictionary[i]+1
# Else initialize the dictionary with the list element as key and value as 1.
else:
freqncyDictionary[i] = 1
# Take a new empty list say modifdlst and store it in a variable.
modifdlst = []
# Loop in the given list using the For loop.
for lstelmt in gvnlst:
# Check if the key in the freqncyDictionary having value even using the if conditional
# statement.
if(freqncyDictionary[lstelmt] % 2 == 0):
# If it is true then append the key value to the above declared empty list modifdlst.
modifdlst.append(lstelmt)
# Print the list after deletion of all the elements from a given list that has an odd
# frequency.
print("The list after deletion of all the elements from a given list that has an odd frequency :", modifdlst)
Output:
The list after deletion of all the elements from a given list that has an odd frequency : [10, 4, 2, 10, 2, 4, 6, 6]
Method #2: Using Dictionary (Hashing, User Input)
Approach:
- Take a dictionary and initialize it to empty using the {} or dict() say freqncyDictionary.
- Give the list as user input using the list(),map(),split(),int functions and store it in a variable.
- Loop in the given list using the For loop.
- Inside the For loop, Check if the list element is present in the dictionary or not using the if conditional statement and ‘in‘ keyword.
- If it is true then increment the count of the list element in the dictionary by 1.
- Else initialize the dictionary with the list element as key and value as 1.
- Take a new empty list say modifdlst and store it in a variable.
- Loop in the given list using the For loop.
- Check if the key in the freqncyDictionary having value even using the if conditional statement.
- If it is true then append the key value to the above declared empty list modifdlst.
- Print the list after deletion of all the elements from a given list that has an odd frequency.
- The Exit of the Program.
Below is the implementation:
# Take a dictionary and initialize it to empty
# using the {} or dict() say freqncyDictionary.
freqncyDictionary = {}
# Give the list as user input using the list(),map(),split(),int functions
# and store it in a variable.
gvnlst = list(
map(int, input('Enter some random list element separated by spaces = ').split()))
# Loop in the given list using the For loop.
for i in gvnlst:
# Inside the For loop,
# Check if the list element is present in the dictionary
# or not using the if conditional statement and 'in' keyword.
if i in freqncyDictionary.keys():
# If it is true then increment the count of the list element
# in the dictionary by 1.
freqncyDictionary[i] = freqncyDictionary[i]+1
# Else initialize the dictionary with the list element as key and value as 1.
else:
freqncyDictionary[i] = 1
# Take a new empty list say modifdlst and store it in a variable.
modifdlst = []
# Loop in the given list using the For loop.
for lstelmt in gvnlst:
# Check if the key in the freqncyDictionary having value even using the if conditional
# statement.
if(freqncyDictionary[lstelmt] % 2 == 0):
# If it is true then append the key value to the above declared empty list modifdlst.
modifdlst.append(lstelmt)
# Print the list after deletion of all the elements from a given list that has an odd
# frequency.
print("The list after deletion of all the elements from a given list that has an odd frequency :", modifdlst)
Output:
Enter some random list element separated by spaces = 1 6 8 2 1 7 6 8 The list after deletion of all the elements from a given list that has an odd frequency : [1, 6, 8, 1, 6, 8]
Method #3: Using Counter() function (Hashing, Static Input)
Approach:
- Import the Counter() function from collections using the import keyword.
- Give the list as static input and store it in a variable.
- Calculate the frequency of all the given list elements using the Counter() function which returns the element and its frequency as key-value pair and store this dictionary in a variable(say freqncyDictionary)
- Take a new empty list say modifdlst and store it in a variable.
- Loop in the given list using the For loop.
- Check if the key in the freqncyDictionary having value even using the if conditional statement.
- If it is true then append the key value to the above declared empty list modifdlst.
- Print the list after deletion of all the elements from a given list that has an odd frequency.
- The Exit of the Program.
Below is the implementation:
# Import the Counter() function from collections using the import keyword.
from collections import Counter
# Give the list as static input and store it in a variable.
gvnlst = [10, 4, 2, 10, 1, 2, 3, 4, 5, 6, 6]
# Calculate the frequency of all the given list elements using the Counter()
# function which returns the element and its frequency as key-value pair
# and store this dictionary in a variable(say freqncyDictionary)
freqncyDictionary = Counter(gvnlst)
# Take a new empty list say modifdlst and store it in a variable.
modifdlst = []
# Loop in the given list using the For loop.
for lstelmt in gvnlst:
# Check if the key in the freqncyDictionary having value even using the if conditional
# statement.
if(freqncyDictionary[lstelmt] % 2 == 0):
# If it is true then append the key value to the above declared empty list modifdlst.
modifdlst.append(lstelmt)
# Print the list after deletion of all the elements from a given list that has an odd
# frequency.
print("The list after deletion of all the elements from a given list that has an odd frequency :", modifdlst)
Output:
The list after deletion of all the elements from a given list that has an odd frequency : [10, 4, 2, 10, 2, 4, 6, 6]
Method #4: Using Counter() function (Hashing, User Input)
Approach:
- Import the Counter() function from collections using the import keyword.
- Give the list as user input using the list(),map(),split(),int functions and store it in a variable.
- Calculate the frequency of all the given list elements using the Counter() function which returns the element and its frequency as key-value pair and store this dictionary in a variable(say freqncyDictionary)
- Take a new empty list say modifdlst and store it in a variable.
- Loop in the given list using the For loop.
- Check if the key in the freqncyDictionary having value even using the if conditional statement.
- If it is true then append the key value to the above declared empty list modifdlst.
- Print the list after deletion of all the elements from a given list that has an odd frequency.
- The Exit of the Program.
Below is the implementation:
# Import the Counter() function from collections using the import keyword.
from collections import Counter
# Give the list as user input using the list(),map(),split(),int functions
# and store it in a variable.
gvnlst = list(
map(int, input('Enter some random list element separated by spaces = ').split()))
# Calculate the frequency of all the given list elements using the Counter()
# function which returns the element and its frequency as key-value pair
# and store this dictionary in a variable(say freqncyDictionary)
freqncyDictionary = Counter(gvnlst)
# Take a new empty list say modifdlst and store it in a variable.
modifdlst = []
# Loop in the given list using the For loop.
for lstelmt in gvnlst:
# Check if the key in the freqncyDictionary having value even using the if conditional
# statement.
if(freqncyDictionary[lstelmt] % 2 == 0):
# If it is true then append the key value to the above declared empty list modifdlst.
modifdlst.append(lstelmt)
# Print the list after deletion of all the elements from a given list that has an odd
# frequency.
print("The list after deletion of all the elements from a given list that has an odd frequency :", modifdlst)
Output:
Enter some random list element separated by spaces = 3 6 2 1 8 3 6 8 The list after deletion of all the elements from a given list that has an odd frequency : [3, 6, 8, 3, 6, 8]
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