Program for ArrayList Elements that Appear More than Once

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:

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

Access the big list of Python Programming Code Examples with actual logical code asked in Programming and Coding Interviews for Python and stand out from the crowd.