Python | Program to print duplicates from a list of integers
Given a list of integers with duplicate elements in it. The task to generate another list, which contains only the duplicate elements. In simple words, the new list should contain the elements which appear more than one.
Examples :
Input : list = [10, 20, 30, 20, 20, 30, 40, 50, -20, 60, 60, -20, -20] Output : output_list = [20, 30, -20, 60] Input : list = [-1, 1, -1, 8] Output : output_list = [-1]
Method 1: Using the Brute Force approach
Python3
# Python program to print# duplicates from a list# of integersdef Repeat(x): _size = len(x) repeated = [] for i in range(_size): k = i + 1 for j in range(k, _size): if x[i] == x[j] and x[i] not in repeated: repeated.append(x[i]) return repeated# Driver Codelist1 = [10, 20, 30, 20, 20, 30, 40, 50, -20, 60, 60, -20, -20]print (Repeat(list1)) # This code is contributed# by Sandeep_anand |
Output
[20, 30, -20, 60]
Output :
[20, 30, -20, 60]
Method 2: Using Counter() function from collection module
Python3
from collections import Counterl1 = [1,2,1,2,3,4,5,1,1,2,5,6,7,8,9,9]d = Counter(l1)print(d)new_list = list([item for item in d if d[item]>1])print(new_list) |
Output
Counter({1: 4, 2: 3, 5: 2, 9: 2, 3: 1, 4: 1, 6: 1, 7: 1, 8: 1})
[1, 2, 5, 9]Method 3: Using count() method
Python3
# program to print duplicate numbers in a given list# provided inputlist = [1, 2, 1, 2, 3, 4, 5, 1, 1, 2, 5, 6, 7, 8, 9, 9]new = [] # defining output list# condition for reviewing every# element of given input listfor a in list: # checking the occurrence of elements n = list.count(a) # if the occurrence is more than # one we add it to the output list if n > 1: if new.count(a) == 0: # condition to check new.append(a)print(new)# This code is contributed by Himanshu Khune |
Output
[1, 2, 5, 9]
Method 4: Using list comprehension method
Python3
def duplicate(input_list): return list(set([x for x in input_list if input_list.count(x) > 1]))if __name__ == '__main__': input_list = [1, 2, 1, 2, 3, 4, 5, 1, 1, 2, 5, 6, 7, 8, 9, 9] print(duplicate(input_list))# This code is contributed by saikot |
Output
[1, 2, 5, 9]
Method 5: Using list-dictionary approach (without any inbuild count function)
Python3
def duplicate(input_list): new_dict, new_list = {}, [] for i in input_list: if not i in new_dict: new_dict[i] = 1 else: new_dict[i] += 1 for key, values in new_dict.items(): if values > 1: new_list.append(key) return new_listif __name__ == '__main__': input_list = [1, 2, 1, 2, 3, 4, 5, 1, 1, 2, 5, 6, 7, 8, 9, 9] print(duplicate(input_list))# This code is contributed by saikot |
Output
[1, 2, 5, 9]
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