python iterate two lists different length
And, if we have more than one list to iterate in parallel?! So far, youve covered how Pythons zip() function works and learned about some of its most important features. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. A convenient way to achieve this is to use dict() and zip() together. Not the answer you're looking for? Not the answer you're looking for? Sometimes, while working with Python list, we can have a problem in which we have to iterate over two list elements. One option is to use itertools.zip_longest (in python 3): Update to handle the slightly more complicated case: This handles the above two cases pretty well: Note even though this works for the above two cases, but it can still break under deeper nested structure, since the case can get complicated very quickly. Apart from the zip() function, Python also offers us the map() function to iterate over multiple lists until all the list elements are exhausted. Time complexity: O(n), where n is the length of the longest list (in this case, n=3).Auxiliary space: O(1), as no extra space is being used. Append each element in original_list2 to the end of original_list1, thus combining the two lists into a single list. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. - Projeto python parte #02, Remove All the Occurrences of an Element From a List in Python, What Is the Difference Between List Methods Append and Extend. Iterate Through List in Python Using Numpy Module. Does Chain Lightning deal damage to its original target first? Please help us improve Stack Overflow. We then use the izip() function to iterate over the lists. If you really need to write code that behaves the same way in both Python 2 and Python 3, then you can use a trick like the following: Here, if izip() is available in itertools, then youll know that youre in Python 2 and izip() will be imported using the alias zip. 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A-143, 9th Floor, Sovereign Corporate Tower, We use cookies to ensure you have the best browsing experience on our website. Use different Python version with virtualenv. That does provide the missing value but not sure how I would make that part of the table during the for loop. PyQGIS: run two native processing tools in a for loop, Mike Sipser and Wikipedia seem to disagree on Chomsky's normal form. itertools.zip_longest(*iterables, fillvalue=None) will do the job for you: If the iterables are of uneven length, missing values are filled-in with fillvalue. List comprehension performs the task of interleaving simultaneously. Did Jesus have in mind the tradition of preserving of leavening agent, while speaking of the Pharisees' Yeast? zip() can provide you with a fast way to make the calculations: Here, you calculate the profit for each month by subtracting costs from sales. Unexpected results of `texdef` with command defined in "book.cls", Existence of rational points on generalized Fermat quintics. Sorting is a common operation in programming. Iterating over single lists, refers to using for loops for iteration over a single element of a single list at a particular step whereas in iterating over multiple lists simultaneously, we refer using for loops for iteration over a single element of multiple lists at a particular step. 2. It returns an iterator that can generate tuples with paired elements from each argument. Ways to Iterate Through List in Python. "compare two list that are different lengths and print a, Python Comparing two lists with different lengths, The philosopher who believes in Web Assembly, Improving the copy in the close modal and post notices - 2023 edition, New blog post from our CEO Prashanth: Community is the future of AI. I just threw it into a function like: I have updated the description outlining a more general problem - could this solution be easily modified? Connect and share knowledge within a single location that is structured and easy to search. How can I detect when a signal becomes noisy? How do I merge two dictionaries in a single expression in Python? rev2023.4.17.43393. stackoverflow Is "in fear for one's life" an idiom with limited variations or can you add another noun phrase to it? zip(fields, values) returns an iterator that generates 2-items tuples. Time Complexity: O(n2)Auxiliary Space: O(n), Method #2 : Using chain() + zip() + cycle(). @MBasith This sorts your data. You can also use sorted() and zip() together to achieve a similar result: In this case, sorted() runs through the iterator generated by zip() and sorts the items by letters, all in one go. How do I get the number of elements in a list (length of a list) in Python? Time complexity: O(n+m), where n is the length of original_list1 and m is the length of original_list2. He's an avid technical writer with a growing number of articles published on Real Python and other sites. New external SSD acting up, no eject option. The map function works as expected in Python 2. This approach can be a little bit faster since youll need only two function calls: zip() and sorted(). Content Discovery initiative 4/13 update: Related questions using a Machine How do I insert elements into multiple lists in python? The time and space complexity of this code is constant time (O(1)) and constant space (O(1)). To subscribe to this RSS feed, copy and paste this URL into your RSS reader. This means that the resulting list of tuples will take the form [(numbers[0], letters[0]), (numbers[1], letters[1]),, (numbers[n], letters[n])]. This function creates an iterator that aggregates elements from each of the iterables. It accepts start, stop, and step as input. Why is a "TeX point" slightly larger than an "American point"? In this tutorial we will discuss in detail all the 11 ways to iterate through list in python which are as follows: 1. We will use zip() and itertools.zip_longest() and explain the differences between them and how to use each one. While inside the loop, we store our information in variables and increment `index`python. Should the alternative hypothesis always be the research hypothesis? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. No spam ever. What screws can be used with Aluminum windows? When youre working with the Python zip() function, its important to pay attention to the length of your iterables. python - Iterate over two lists with different lengths - Stack Overflow Iterate over two lists with different lengths Ask Question Asked 5 years, 11 months ago Modified 5 years, 11 months ago Viewed 28k times 13 I have 2 lists of numbers that can be different lengths, for example: list1 = [1, 2, -3, 4, 7] list2 = [4, -6, 3, -1] Find centralized, trusted content and collaborate around the technologies you use most. Similarly, the space complexity is also constant, as the code only creates three tuples with three elements each, and the number of tuples created is also fixed and does not depend on the input size. Then, you use the unpacking operator * to unzip the data, creating two different lists (numbers and letters). python doc: zip lists in python: stackoverflow: Combining two lists: stackoverflow: Python:get a couple of values from two different list: stackoverflow: Is there a better way to iterate over two lists, getting one element from each list for each iteration? With a single iterable argument, it returns an iterator of 1-tuples. It accepts iterable objects such as lists and strings as input. The iteration only stops when longest is exhausted. When you consume the returned iterator with list(), you get a list of tuples, just as if you were using zip() in Python 3. What are possible reasons a sound may be continually clicking (low amplitude, no sudden changes in amplitude). How small stars help with planet formation. In your case you should probably just check if the index is longer than the sequence: Or use itertools.zip_longest (or itertools.izip_longest on python-2.x) and check for some fillvalue (i.e. What PHILOSOPHERS understand for intelligence? This composes a list comprehension using zip_longest from itertools (which is part of the standard library) to interleave items from both lists into a tuple, which by default uses None as the fillvalue.. In these cases, the number of elements that zip() puts out will be equal to the length of the shortest iterable. Now you have the following lists of data: With this data, you need to create a dictionary for further processing. If you call zip() with no arguments, then you get an empty list in return: In this case, your call to the Python zip() function returns a list of tuples truncated at the value C. When you call zip() with no arguments, you get an empty list. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Content Discovery initiative 4/13 update: Related questions using a Machine How do I merge two dictionaries in a single expression in Python? This means that the tuples returned by zip() will have elements that are paired up randomly. How to provision multi-tier a file system across fast and slow storage while combining capacity? Another approach to iterate over multiple lists simultaneously is to use the enumerate () function. In Python 2.x, zip() and zip_longest() used to return list, and izip() and izip_longest() used to return iterator. How to iterate over files in directory using Python? Unsubscribe any time. The Python zip () function makes it easy to also zip more than two lists. Is there a zip-like function that pads to longest length? Python for loops are a powerful tool, so it is important for programmers to understand their versatility. acknowledge that you have read and understood our, Data Structure & Algorithm Classes (Live), Data Structures & Algorithms in JavaScript, Data Structure & Algorithm-Self Paced(C++/JAVA), Full Stack Development with React & Node JS(Live), Android App Development with Kotlin(Live), Python Backend Development with Django(Live), DevOps Engineering - Planning to Production, GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam, Interview Preparation For Software Developers, Getting all CSV files from a directory using Python. Lets discuss certain ways in which this task can be performed. How to check if an SSM2220 IC is authentic and not fake? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Can you explain what the output should be? listA = [1, 2, 3, 4, 5, 6] listB = [10, 20, 30, 40] for a,b in zip(listA,listB): print(a,b) Output: 1 10 2 20 3 30 4 40 Use itertools.zip_longest () to Iterate Through Two Lists Interlocking pairs of teeth on both sides of the zipper are pulled together to close an opening. According to the official documentation, Pythons zip() function behaves as follows: Returns an iterator of tuples, where the i-th tuple contains the i-th element from each of the argument sequences or iterables. Example Get your own Python Server In this case, the zip_longest() function replaces and maps the equivalent element with a None value. Finding valid license for project utilizing AGPL 3.0 libraries. Data Structures & Algorithms in Python; Explore More Self-Paced Courses; Programming Languages. The zip() function then iterates over the two lists in parallel only 2 times the length(list02)=2. The range(start, stop, step) function enables us to get a sequence of numbers from a defined range of values. Let us study them one by one below: Using for loop. Let's discuss certain ways in which this task can be performed. He's a self-taught Python developer with 6+ years of experience. 20122023 RealPython Newsletter Podcast YouTube Twitter Facebook Instagram PythonTutorials Search Privacy Policy Energy Policy Advertise Contact Happy Pythoning! Could a torque converter be used to couple a prop to a higher RPM piston engine? Commenting Tips: The most useful comments are those written with the goal of learning from or helping out other students. Can someone please tell me what is written on this score? Isnt that simple? Perhaps you can find some use cases for this behavior of zip()! To learn more, see our tips on writing great answers. Pythons zip() function is defined as zip(*iterables). Also you use insert a lot. For a more general solution, you can see here. On the other hand, the latter does not follow those criteria. To use a version before Python 3.0, we use the izip() function instead of the zip() function to iterate over multiple lists. Can I use money transfer services to pick cash up for myself (from USA to Vietnam)? Input : test_list1 = [3, 8, 7], test_list2 = [5, 7, 3, 0, 1, 8]Output : [3, 5, 8, 7, 7, 3, 3, 0, 8, 1, 7, 8]Explanation : Alternate elements from 1st list are printed in cyclic manner once it gets exhausted. Youll unpack this definition throughout the rest of the tutorial. Another way using zip_longest and chain from itertools: Thanks for contributing an answer to Stack Overflow! You can use the Python zip() function to make some quick calculations. I am partially able to accomplish this and print the values that are missing in list_2. These are all ignored by zip() since there are no more elements from the first range() object to complete the pairs. The list uses comma-separated values within square brackets to store data. Process of finding limits for multivariable functions, Put someone on the same pedestal as another, How to turn off zsh save/restore session in Terminal.app, Use Raster Layer as a Mask over a polygon in QGIS. Auxiliary Space: O(n), where n is the number of elements in the new paired list. zip() is available in the built-in namespace. Theres no restriction on the number of iterables you can use with Pythons zip() function. Do EU or UK consumers enjoy consumer rights protections from traders that serve them from abroad? But the drawback here is that we might have to concatenate the list and hence would consume more memory than desired. If you forget this detail, the final result of your program may not be quite what you want or expect. acknowledge that you have read and understood our, Data Structure & Algorithm Classes (Live), Data Structures & Algorithms in JavaScript, Data Structure & Algorithm-Self Paced(C++/JAVA), Full Stack Development with React & Node JS(Live), Android App Development with Kotlin(Live), Python Backend Development with Django(Live), DevOps Engineering - Planning to Production, GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam, Python | Iterate over multiple lists simultaneously, Important differences between Python 2.x and Python 3.x with examples, Statement, Indentation and Comment in Python, How to assign values to variables in Python and other languages, Python | NLP analysis of Restaurant reviews, Adding new column to existing DataFrame in Pandas, How to get column names in Pandas dataframe. We can iterate over lists simultaneously in ways: We can also specify a default value instead of None in zip_longest(), Time complexity: O(n), where n is the length of the longest list. If you call dict() on that iterator, then youll be building the dictionary you need. This iterator generates a series of tuples containing elements from each iterable. What sort of contractor retrofits kitchen exhaust ducts in the US? Another approach to iterate over multiple lists simultaneously is to use the enumerate() function. rightBarExploreMoreList!=""&&($(".right-bar-explore-more").css("visibility","visible"),$(".right-bar-explore-more .rightbar-sticky-ul").html(rightBarExploreMoreList)), Loop or Iterate over all or certain columns of a dataframe in Python-Pandas. There are multiple ways through which we can iterate the list in python programming. With a solution like this, we can loop until the index is equal to the length of the smaller list. However, since zipped holds an empty iterator, theres nothing to pull out, so Python raises a StopIteration exception. ['ArithmeticError', 'AssertionError', 'AttributeError', , 'zip'], [(1, 'a', 4.0), (2, 'b', 5.0), (3, 'c', 6.0)], [(1, 'a', 0), (2, 'b', 1), (3, 'c', 2), ('? Recommended Video CourseParallel Iteration With Python's zip() Function, Watch Now This tutorial has a related video course created by the Real Python team. Then we could sort the new list and while iterating over it, we could check the existence of elements of the third list in the original ones. The zip function accepts multiple lists, strings, etc., as input. How can I make inferences about individuals from aggregated data? For each element, append it to the end of original_list1 using the append() method.4. Theres a question that comes up frequently in forums for new Pythonistas: If theres a zip() function, then why is there no unzip() function that does the opposite?. That works fine for small lists, but if you have huge lists, you should use itertools.izip() instead, because it returns an iterator of tuples. This is because we are iterating over all the elements of original_list2 and appending each of them to original_list1. Use the len () function to determine the length of the list, then start at 0 and loop your way through the list items by referring to their indexes. That's what the generator expression below does. If given lists of different lengths, the resulting combination will only be as long as the smallest list passed. Should the alternative hypothesis always be the research hypothesis? With this technique, you can easily overwrite the value of job. The iteration will continue until the longest iterable is exhausted: Here, you use itertools.zip_longest() to yield five tuples with elements from letters, numbers, and longest. Note: If you want to dive deeper into Python for loops, check out Python for Loops (Definite Iteration). zip() can accept any type of iterable, such as files, lists, tuples, dictionaries, sets, and so on. However, for other types of iterables (like sets), you might see some weird results: In this example, s1 and s2 are set objects, which dont keep their elements in any particular order. What I want to obtain is something similar to this: 1,4 2,5 3,6 ,7 I have thought of using the zip function but it doesn't seem to work with different length lists as by using the following code: for l1, l2 in list1, list2: print (l1,l2) I get this: 1,4 2,5 3,6 Method #2 : Using chain() This is the method similar to above one, but its slightly more memory efficient as the chain() is used to perform the task and creates an iterator internally. The resulting list is truncated to the length of the shortest input iterable. After applying the specified function, it maps the iterable data elements and returns a tuple after mapping the values. Method #2: Using List slicing Power of list slicing of python can also be used to perform this particular task. Leodanis is an industrial engineer who loves Python and software development. Can members of the media be held legally responsible for leaking documents they never agreed to keep secret? Why does the second bowl of popcorn pop better in the microwave? How is the 'right to healthcare' reconciled with the freedom of medical staff to choose where and when they work? You can also use Pythons zip() function to iterate through sets in parallel. How to upgrade all Python packages with pip, Get difference between two lists with Unique Entries. When you compare lists for equality, you're checking whether the lists are the same length and whether each item in the list is equal. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. In this case, youll get a StopIteration exception: When you call next() on zipped, Python tries to retrieve the next item. tuples, sets, or dictionaries ). Examples: Input : test_list1 = ['a', 'b', 'c'], test_list2 = [5, 7, 3, 0, 1, 8, 4] Say you have a list of tuples and want to separate the elements of each tuple into independent sequences. I have 2 lists of numbers that can be different lengths, for example: I need to iterate over these with the function: but can't figure out how to deal with the range as the shorter list will become "out of range" if I use the max length. How do I iterate through two lists in parallel? Actually making the third list a set would be better. Notice how data1 is sorted by letters and data2 is sorted by numbers. ', 4)], zip() argument 2 is longer than argument 1,
