Method 1:
list(set([val for idx, val in enumerate(input_list) if val in input_list[idx+1:]]))
Explanation: [val for idx, val in enumerate(input_list) if val in input_list[idx+1:]] is a list comprehension, that returns an element, if the same element is present from it's current position, in list, the index.
Example: input_list = [42,31,42,31,3,31,31,5,6,6,6,6,6,7,42]
starting with the first element in list, 42, with index 0, it checks if the element 42, is present in input_list[1:] (i.e., from index 1 till end of list) Because 42 is present in input_list[1:], it will return 42.
Then it goes to the next element 31, with index 1, and checks if element 31 is present in the input_list[2:] (i.e., from index 2 till end of list), Because 31 is present in input_list[2:], it will return 31.
similarly it goes through all the elements in the list, and will return only the repeated/duplicate elements into a list.
Then because we have duplicates, in a list, we need to pick one of each duplicate, i.e. remove duplicate among duplicates, and to do so, we do call a python built-in named set(), and it removes the duplicates,
Then we are left with a set, but not a list, and hence to convert from a set to list, we use, typecasting, list(), and that converts the set of elements to a list.
Method 2:
def dupes(ilist):
temp_list = [] # initially, empty temporary list
dupe_list = [] # initially, empty duplicate list
for each in ilist:
if each in temp_list: # Found a Duplicate element
if not each in dupe_list: # Avoid duplicate elements in dupe_list
dupe_list.append(each) # Add duplicate element to dupe_list
else:
temp_list.append(each) # Add a new (non-duplicate) to temp_list
return dupe_list
Explanation: Here We create two empty lists, to start with. Then keep traversing through all the elements of the list, to see if it exists in temp_list (initially empty). If it is not there in the temp_list, then we add it to the temp_list, using append method.
If it already exists in temp_list, it means, that the current element of the list is a duplicate, and hence we need to add it to dupe_list using append method.