Check for duplicates in a list using Set & by comparing sizesTo check if a list contains any duplicate element follow the following steps, Show
We have created a function that follows the above Algo i.e. Now let’s use this function to check if our list contains any duplicate or not i.e. listOfElems = ['Hello', 'Ok', 'is', 'Ok', 'test', 'this', 'is', 'a', 'test'] result = checkIfDuplicates_1(listOfElems) if result: print('Yes, list contains duplicates') else: print('No duplicates found in list') Output Yes, list contains duplicates Complexity Analysis of this solution. Advertisements As we are creating a set from list, so complexity will be n(log(n)). Comparing size is a O(1) operation. So, complexity of this solution is n(log(n)). Even in best scenario i.e. if list contains only duplicated element, still this solution’s complexity will be n(log(n)) because we are just adding all the elements from list to set. Let’s look into an another better solution, Check if a list has duplicate Elements using SetsWe know that sets in Python contain only unique elements. We can use this property of sets to check if a list has duplicate elements or not. For this, we will create a set from the elements of the list. After that, we will check the size of the list and the set. If the size of both the objects are equal, it will confirm that the list has no duplicate elements. If the size of the set is greater than the list, it will mean that the list contains duplicate elements. We can understand this from the following example. Output: In the above approach, we need to create a set from all the elements of the list. After that, we also check the size of the set and the list. These operations are very costly. Instead of using this approach, we can search only for the first duplicate element. To do this, we will start from the first element of the list and will keep adding them to the set. Before adding the elements to the set, we will check if the element is already present in the set or not. If yes, the list contains duplicate elements. If we are able to add each element of the list to the set, the list does not contain any duplicate element. This can be understood from the following example. def check_duplicate(l): visited = set() has_duplicate = False for element in l: if element in visited: print("The list contains duplicate elements.") has_duplicate = True break else: visited.add(element) if not has_duplicate: print("List has no duplicate elements.") list1 = [1, 2, 3, 4, 5, 6, 7] print("List1 is:", list1) check_duplicate(list1) list2 = [1, 2, 1, 2, 4, 6, 7] print("List2 is:", list2) check_duplicate(list2)Output: List1 is: [1, 2, 3, 4, 5, 6, 7] List has no duplicate elements. List2 is: [1, 2, 1, 2, 4, 6, 7] The list contains duplicate elements.Check If a Python List Has DuplicatesI have the following list and first I want to know if this list contains any duplicates: We can see if this list has any duplicates by using the properties of a Python set. Here is what happens when I convert this list to a set: >>> set(planets) {'earth', 'mars', 'jupiter', 'mercury'}Ignore the fact that the order of the elements has changed (considering that a set is unordered). The important thing to notice is that the duplicate string “mars” has disappeared because a set only contains unique values. So, to check if a list contains any duplicates we can simply compare the size of the list with the size of the set. If they are different the list contains duplicates. The size of the list and the set are: >>> len(planets) 5 >>> len(set(planets)) 4We can write a function that uses a conditional statement to verify if a list contains any duplicates and that returns True if it does. >>> def has_duplicates(values): ... if len(values) != len(set(values)): ... return True ... else: ... return False ... >>> >>> has_duplicates(planets) TrueLet’s redefine the list, remove the duplicate string and pass the list to our function again: >>> planets = ['mercury', 'earth', 'mars', 'jupiter'] >>> has_duplicates(planets) FalseEt voilà, this time it returns False as we expected. Check if the list contains duplicate elements in PythonPosted: 2020-12-09 / Tags: Python, List Tweet This article describes how to check if there are duplicate elements (= if all elements are unique) in a list in Python for the following cases:
See the following article for removing or extracting duplicate elements from the list.
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