Python Program for Array/List Elements that Appear More than Once

In the previous article, we have discussed Python Program to Remove Elements from the Array/List Which Occurs More than k Times

Given a list, and the task is to print all the elements from a given list that appears more than once in python.

Examples:

Example1:

Input:

Given List = [20, 30, 40, 50, 20, 50]

Output:

The Elements from a given list [20, 30, 40, 50, 20, 50] that appears more than once : 
20 50

Example2:

Input:

Given List = [15, 25, 35, 25, 15, 40]

Output:

The Elements from a given list [15, 25, 35, 25, 15, 40] that appears more than once : 
15 25

Program for Array/List Elements that Appear More than Once in Python

Below are the ways to print all the elements from a given list that appears more than once in python:

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 above-calculated frequency dictionary using the For loop
Check if the key in the freqncyDictionary having a value greater than 1 using the if conditional statement.
If it is true then append the key value to the above declared empty list modifdlst.
Print all the elements from a given list that appears more than once.
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 = [20, 30, 40, 50, 20, 50]
# 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 above calculated frequency dictionary using the For loop
for key in freqncyDictionary:
  # Check if the key in the freqncyDictionary having value greater than 1
  # using the if conditional statement.

    if(freqncyDictionary[key] > 1):
      # If it is true then append the key value to the above declared empty list modifdlst.
        modifdlst.append(key)
# Print all the elements from a given list that appears more than once.
print("The Elements from a given list", gvnlst,
      "that appears more than once : ")
print(*modifdlst)

Output:

The Elements from a given list [20, 30, 40, 50, 20, 50] that appears more than once : 
20 50

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 above-calculated frequency dictionary using the For loop
Check if the key in the freqncyDictionary having a value greater than 1 using the if conditional statement.
If it is true then append the key value to the above declared empty list modifdlst.
Print all the elements from a given list that appears more than once.
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 above calculated frequency dictionary using the For loop
for key in freqncyDictionary:
  # Check if the key in the freqncyDictionary having value greater than 1
  # using the if conditional statement.

    if(freqncyDictionary[key] > 1):
      # If it is true then append the key value to the above declared empty list modifdlst.
        modifdlst.append(key)
# Print all the elements from a given list that appears more than once.
print("The Elements from a given list", gvnlst,
      "that appears more than once : ")
print(*modifdlst)

Output:

Enter some random list element separated by spaces = 15 25 35 25 15 40
The Elements from a given list [15, 25, 35, 25, 15, 40] that appears more than once : 
15 25

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 above-calculated frequency dictionary using the For loop
Check if the key in the freqncyDictionary having a value greater than 1 using the if conditional statement.
If it is true then append the key value to the above declared empty list modifdlst.
Print all the elements from a given list that appears more than once.
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 = [20, 30, 40, 50, 20, 50]
# 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 above calculated frequency dictionary using the For loop
for key in freqncyDictionary:
  # Check if the key in the freqncyDictionary having value greater than 1
  # using the if conditional statement.

    if(freqncyDictionary[key] > 1):
      # If it is true then append the key value to the above declared empty list modifdlst.
        modifdlst.append(key)
# Print all the elements from a given list that appears more than once.
print("The Elements from a given list", gvnlst,
      "that appears more than once : ")
print(*modifdlst)

Output:

The Elements from a given list [20, 30, 40, 50, 20, 50] that appears more than once : 
20 50

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 above-calculated frequency dictionary using the For loop
Check if the key in the freqncyDictionary having a value greater than 1 using the if conditional statement.
If it is true then append the key value to the above declared empty list modifdlst.
Print all the elements from a given list that appears more than once.
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 above calculated frequency dictionary using the For loop
for key in freqncyDictionary:
  # Check if the key in the freqncyDictionary having value greater than 1
  # using the if conditional statement.

    if(freqncyDictionary[key] > 1):
      # If it is true then append the key value to the above declared empty list modifdlst.
        modifdlst.append(key)
# Print all the elements from a given list that appears more than once.
print("The Elements from a given list", gvnlst,
      "that appears more than once : ")
print(*modifdlst)

Output:

Enter some random list element separated by spaces = 1 2 4 4 2 3 6 1
The Elements from a given list [1, 2, 4, 4, 2, 3, 6, 1] that appears more than once : 
1 2 4

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