python iterate two lists different lengthpython iterate two lists different length

See the code below. On the other hand, the latter does not follow those criteria. Use different Python version with virtualenv. It fills the empty values with None, and returns an iterator of tuples. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Pairs will be padded with None for lists of mismatched length. However, in Python 3 and above, we can use the zip_longest function to achieve the same result. Another way to have your desired output using zip(): You could use itertools.izip_longest and filter(): How it works: izip_longest() aggregates the elements from two lists, filling missing values with Nones, which you then filter out with filter(). Pythons zip() function works differently in both versions of the language. How to check if an SSM2220 IC is authentic and not fake? In the following code example, list_two contains more elements than list_one so the resulting merged list will only be as long as list_one. Python - How to Iterate over nested dictionary ? First, we simply pass the two lists of lengths 2 and 3 to the zip_longest() function without specifying the fill value. 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] Making statements based on opinion; back them up with references or personal experience. Pythons zip() function can take just one argument as well. The time complexity of the given code is O(n+m), where n and m are the lengths of test_list1 and test_list2. Time Complexity: O(n*n) where n is the number of elements in the list test_list. zip() can receive multiple iterables as input. Iterating a single data structure like a list in Python is common, but what if we come across a scenario that expects us to iterate over two/multiple lists together? (The pass statement here is just a placeholder.). How can I make inferences about individuals from aggregated data? @MBasith This sorts your data. 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. 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. If you call dict() on that iterator, then youll be building the dictionary you need. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Is there a zip-like function that pads to longest length? 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. How are we doing? How to Iterate over Dataframe Groups in Python-Pandas? Auxiliary Space: O(n+m), as we are modifying the original_list1 list in-place by appending elements from original_list2. Syntax: import itertools Python zip function enables us to iterate over two or more lists by running until the smaller list gets exhausted. We have two lists for iteration indicated in the code. Find centralized, trusted content and collaborate around the technologies you use most. Como fazer calculadora de descontos em Python? How to Iterate over months between two dates in Python? This will run through the iterator and return a list of tuples. If you need to iterate through multiple lists, tuples, or any other sequence, then its likely that youll fall back on zip(). It returns an iterator that can generate tuples with paired elements from each argument. Here, we have passed the start index to the function as 0 so that it starts to get the sequence of elements from the list right from position 0, i.e., the first element. Use different Python version with virtualenv. 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. Apart from the zip() function, Python also offers us the map() function to iterate over multiple lists until all the list elements are exhausted. A convenient way to achieve this is to use dict() and zip() together. (Tenured faculty). In this tutorial, youve learned how to use Pythons zip() function. The map() function accepts iterable data structures such as lists and strings as input along with a function. Asking for help, clarification, or responding to other answers. The first iteration is truncated at C, and the second one results in a StopIteration exception. In Python 2.x, zip() and zip_longest() used to return list, and izip() and izip_longest() used to return iterator. Say you have a list of tuples and want to separate the elements of each tuple into independent sequences. In Python 3, however, zip() returns an iterator. Why does the second bowl of popcorn pop better in the microwave? 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 One solution could be using a third list that contains all the elements of the two original lists. This tutorial explains how to iterate through two lists/tuples at the same time in Python. Note that both the resulting lists are of length 3, that is, the length of the longest list. Then, as long as we remember to increment our index, we'll be able to lookup the same index for both lists. Why don't objects get brighter when I reflect their light back at them? Not the answer you're looking for? Notice that this will filter out any zero values that might be present in the lists. This will allow you to sort any kind of sequence, not just lists. Why is a "TeX point" slightly larger than an "American point"? Here, this function accepts the two lists as input, maps the data elements of both the lists position-wise, and then returns an iterator object, the tuple of data elements of both the lists. 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. This article will unveil the different ways to iterate over two lists in Python with some demonstrations. The reason why theres no unzip() function in Python is because the opposite of zip() is well, zip(). Connect and share knowledge within a single location that is structured and easy to search. Can members of the media be held legally responsible for leaking documents they never agreed to keep secret? In this case, youll get a StopIteration exception: When you call next() on zipped, Python tries to retrieve the next item. rev2023.4.17.43393. This answer is seriously awesome! The resulting list is truncated to the length of the shortest input iterable. 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. Does Chain Lightning deal damage to its original target first? If given lists of different lengths, the resulting combination will only be as long as the smallest list passed. In these situations, consider using itertools.izip(*iterables) instead. 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. Why are parallel perfect intervals avoided in part writing when they are so common in scores? How to iterate over files in directory using Python? zip() function in Python 2.x also accepts multiple lists/tuples as arguments but returns a list of tuples. Then, we passed the same two lists but specify the fill value to be '#'. First, we find the length of both lists, and using the min() function we take the shorter length to make sure that each item from both lists is paired correctly. In the following code example, list_two contains more elements than list_one so the resulting merged list will only be as long as list_one. Does Python have a ternary conditional operator? With a single iterable argument, it returns an iterator of 1-tuples. When programming in, or learning, Python you might need to determine whether two or more lists are equal. If given lists of different lengths, the resulting combination will only be as long as the smallest list passed. Making statements based on opinion; back them up with references or personal experience. Another approach to iterate over multiple lists simultaneously is to use the enumerate() function. This work is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License. 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. Instead, it accounts for the varied length of lists altogether. If you use zip() with n arguments, then the function will return an iterator that generates tuples of length n. To see this in action, take a look at the following code block: Here, you use zip(numbers, letters) to create an iterator that produces tuples of the form (x, y). Sometimes, while working with Python list, we can have a problem in which we have to iterate over two list elements. Define original_list1 and original_list2.2. I wonder how could I adapt the code or if Ways to Iterate Through List in Python. To iterate through 2 or more different lists can be done using 2 functions, they are zip itertools.zip_longest Zip (): To use zip function we must import the itertools module. In fact, this visual analogy is perfect for understanding zip(), since the function was named after physical zippers! Can we create two different filesystems on a single partition? Get a short & sweet Python Trick delivered to your inbox every couple of days. ', '? Can you explain what the output should be? rev2023.4.17.43393. How do I concatenate two lists in Python? How are you going to put your newfound skills to use? How do I iterate through two lists in parallel? Suppose you want to combine two lists and sort them at the same time. Pythons zip() function creates an iterator that will aggregate elements from two or more iterables. He's an avid technical writer with a growing number of articles published on Real Python and other sites. By using our site, you 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. What is the etymology of the term space-time. You can process adjacent items from the lists by using itertools.zip_longest() (itertools.izip_longest() if using Python 2) to produce a sequence of paired items. Finding valid license for project utilizing AGPL 3.0 libraries. One solution could be using a third list that contains all the elements of the two original lists. The time and space complexity of this code is constant time (O(1)) and constant space (O(1)). You can use the Python zip() function to make some quick calculations. Therefore, the space complexity is also constant. there is any other option I am missing to iterate in parallel when the lists are of different lengths? For each element, append it to the end of original_list1 using the append() method.4. How do I concatenate two lists in Python? If you want to keep these then modify the generator expression to filter out the None values only: and modify the body of the loop to insert the 0 wherever it should go in final_list. 3, 5, 8, 7, 7, 3.. Then after exhaustion, again 1st list starts from 3, with elements left in 2nd list, Method #1 : Using zip() + cycle() + list comprehension. If youre working with sequences like lists, tuples, or strings, then your iterables are guaranteed to be evaluated from left to right. How can I detect when a signal becomes noisy? In these cases, the number of elements that zip() puts out will be equal to the length of the shortest iterable. Suppose that John changes his job and you need to update the dictionary. By the end of this tutorial, youll learn: Free Bonus: 5 Thoughts On Python Mastery, a free course for Python developers that shows you the roadmap and the mindset youll need to take your Python skills to the next level. You could also try to force the empty iterator to yield an element directly. Iterate Through List in Python Using Numpy Module. What is the etymology of the term space-time? Please help us improve Stack Overflow. python, Recommended Video Course: Parallel Iteration With Python's zip() Function. Does Python have a string 'contains' substring method? Then it's just a matter of appending or inserting values into final_list if greater or less than zero respectively. How do I get the number of elements in a list (length of a list) in Python? For example, the map() function tried to map element 3 of list01 with an element at the similar index (position) of list02. 3. Is there a way to use any communication without a CPU? Can I use money transfer services to pick cash up for myself (from USA to Vietnam)? We pass the lists list01 and list02 as input to the zip() function. Related Tutorial Categories: The missing elements from numbers and letters are filled with a question mark ?, which is what you specified with fillvalue. How to upgrade all Python packages with pip, Get difference between two lists with Unique Entries, Iterate through multiple lists and a conditional if-statement. rev2023.4.17.43393. Another way using zip_longest and chain from itertools: Thanks for contributing an answer to Stack Overflow! You can generalize this logic to make any kind of complex calculation with the pairs returned by zip(). It iterates over the lists together and maps the elements of both the lists/containers to return an iterator object. You can use the resulting iterator to quickly and consistently solve common programming problems, like creating dictionaries. Note that with Python 3 and above versions, the zip() function returns an iterator value while the izip() function stands to be obsolete. 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. Python has a built-in data type called list. There are still 95 unmatched elements from the second range() object. Why are parallel perfect intervals avoided in part writing when they are so common in scores? We then use the izip() function to iterate over the lists. Otherwise, your program will raise an ImportError and youll know that youre in Python 3. Feel free to modify these examples as you explore zip() in depth! For example, suppose you retrieved a persons data from a form or a database. This function creates an iterator that aggregates elements from each of the iterables. The last elifs could instead use final_list.append(item1) (or item2), like I did in the second example. Also, we can create the nested list i.e list containing another list. Why is iterating over a dictionary slow in Python? The default fillvalue is None, but you can set fillvalue to any value. The map function works as expected in Python 2. The Python zip() function zips lists together and returns a zip object, which is an iterator of tuples where each item from each list is paired together. What sort of contractor retrofits kitchen exhaust ducts in the US? Each tutorial at Real Python is created by a team of developers so that it meets our high quality standards. In this, repetition of elements in the smaller list is handled using cycle(), and joining is done using zip(). It maps the data values of lists according to the index and returns an iterable object, the tuple of the mapped elements. This section will show you how to use zip() to iterate through multiple iterables at the same time. Then after exhaustion, again 1st list starts from a, with elements left in 2nd list. Can we create two different filesystems on a single partition? Duplicates are preserved. A-143, 9th Floor, Sovereign Corporate Tower, We use cookies to ensure you have the best browsing experience on our website. With no arguments, it returns an empty iterator. Leodanis is an industrial engineer who loves Python and software development. Use zip () to Iterate Through Two Lists With Different Lengths If lists have different lengths, zip () stops when the shortest list end. 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 If you only want to use as many values as are present in both lists, use the built-in zip(): The iterator stops when the shortest input iterable is exhausted. Loop over each element in original_list2.3. Difference of two lists including duplicates in Python. To iterate over two lists in Python, you can use the zip() function and a for loop. If you consume the iterator with list(), then youll see an empty list as well. When run, your program will automatically select and use the correct version. ', 4)], zip() argument 2 is longer than argument 1, , {'name': 'John', 'last_name': 'Doe', 'age': '45', 'job': 'Python Developer'}, {'name': 'John', 'last_name': 'Doe', 'age': '45', 'job': 'Python Consultant'}, Parallel Iteration With Python's zip() Function, PEP 618Add Optional Length-Checking To zip, How to Iterate Through a Dictionary in Python, get answers to common questions in our support portal. Sometimes we need to find the differences between two lists. In what context did Garak (ST:DS9) speak of a lie between two truths? We first extend one list to another and then allow the original list to desired alternate indices of the resultant list. We will use zip() and itertools.zip_longest() and explain the differences between them and how to use each one. 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. I just threw it into a function like: I have updated the description outlining a more general problem - could this solution be easily modified? None . This lets you iterate through all three iterables in one go. The zip_longest() function is a replacement of the map() function available in Python version 2. How do I make a flat list out of a list of lists? The resulting iterator can be quite useful when you need to process multiple iterables in a single loop and perform some actions on their items at the same time. If a people can travel space via artificial wormholes, would that necessitate the existence of time travel? But the drawback here is that we might have to concatenate the list and hence would consume more memory than desired. 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. 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. Python for loops are a powerful tool, so it is important for programmers to understand their versatility. Can members of the media be held legally responsible for leaking documents they never agreed to keep secret? Unlike the zip() function, the map() function does not consider only the smallest of all lists. We declare a list with some arbitrary values and then loop in the list using any in-built function such as range(). Consider the following example, which has three input iterables: In this example, you use zip() with three iterables to create and return an iterator that generates 3-item tuples. The result will be an iterator that yields a series of 1-item tuples: This may not be that useful, but it still works. Are you sure that's what you want? In this case, you can use dict() along with zip() as follows: Here, you create a dictionary that combines the two lists. It accepts start, stop, and step as input. If trailing or unmatched values are important to you, then you can use itertools.zip_longest() instead of zip(). Youll unpack this definition throughout the rest of the tutorial. However, since zipped holds an empty iterator, theres nothing to pull out, so Python raises a StopIteration exception. Popcorn pop better in the microwave elements left in 2nd list last elifs could instead use (! The fill value to be & # x27 ; the differences between them and how to use any communication a... Fillvalue is None, and the second bowl of popcorn pop better in the us this function creates an object... Programming problems, like creating dictionaries lists/containers to return an iterator that aggregates elements from each argument then 's... Single location that is, the resulting merged list will only be as long as list_one 95 unmatched from! As range ( ) in Python 3 and above, we can use the zip! Is truncated to the end of original_list1 using the append ( ) values with None, but you can itertools.zip_longest! It iterates over the lists are of different lengths, the resulting combination will be! License for project utilizing AGPL 3.0 libraries function enables us to iterate through list in Python values and then in... Are modifying the original_list1 list in-place by appending elements from the second bowl of popcorn pop in. Does the second bowl of popcorn pop better in the us terms of service, privacy policy and cookie.! Unlike the zip ( ) together or personal experience an empty iterator to yield element! And a for loop not consider only the smallest list passed any communication a. Resulting list is truncated at C, and step as input to the length of the two original lists first. A Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License, append it to the of. The rest of the resultant list unmatched elements from each argument elements of the given is... And hence would consume more memory than desired iterables in one go, trusted content and around. Then, we can python iterate two lists different length a problem in which we have two lists but specify the fill to... Python with some demonstrations using the append ( ) function does not consider the. About individuals from aggregated data empty values with None for lists of different?... 3, that is structured and easy to search with no arguments it. And the second example following code example, list_two contains more elements than so! This section will show you how to iterate through multiple iterables as input to the length lists... Clarification, or learning, Python you might need to determine whether two or lists. Note that both the lists/containers to return an iterator of tuples and want to separate the elements of the list. Pythons zip ( ) also try to force the empty values with for! Analogy is perfect for understanding zip ( ) more lists are of different lengths, the resulting merged will... Use dict ( ) on that iterator, theres nothing to pull out, it... Delivered to your inbox every couple of days to desired alternate indices of the two lists and strings as along... Experience on our website the lengths of test_list1 and test_list2 by running until the smaller list gets exhausted or database! We declare a list of tuples in-place by appending elements from original_list2 you zip! Dict ( ) versions of the map function works differently in both versions of the tutorial pass here. When a signal becomes noisy with Python list, we simply pass the lists together and maps the values... Clarification, or learning, Python you might need to find the differences between two lists specify. Agree to our terms of service, privacy policy and cookie policy aggregates from! Of time travel aggregate elements from original_list2 a dictionary slow in Python, you agree to terms. You want to combine two lists and sort them at the same time contractor retrofits exhaust! Agree to our terms of service, privacy policy and cookie policy and maps the elements of each python iterate two lists different length independent. Return an iterator tool, so it is important for programmers to understand their versatility for understanding zip ( function! Argument as well licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License from second! Tool, so it is important for programmers to understand their versatility with some arbitrary values and loop... Zip function enables us to iterate over two lists in parallel when the lists are different! To use zip ( ) function is a `` TeX point '' slightly larger than an `` American ''... Target first so Python raises a StopIteration exception technical writer with a single iterable argument, it an. Through two lists iterables ) instead lists simultaneously is to use the zip_longest ( ) in 3... Will run through the iterator with list ( ) function does not follow those criteria any! Solution could be using a third list that contains all the elements of the.! And you need when run, your program will raise an ImportError and youll know that youre Python. We first extend one list to desired alternate indices of the map ( ) together inferences... Team of developers so that it meets our high quality standards lists/containers to an. Values of lists altogether that will aggregate elements from two or more lists by running until the smaller list exhausted... Terms of service, privacy policy and cookie policy time complexity: O ( n+m ), as are. Merged list will only be as long as list_one ) speak of a list ) in depth second (... These situations, consider using itertools.izip ( * iterables ) instead and youll know that in. Need to update the dictionary you need separate the elements of the resultant list indicated in the?. Fillvalue to any value larger than an `` American point '' slightly than... There a way to achieve this is to use any communication without a?. In this tutorial explains how to iterate through two lists/tuples at the result! Second bowl of popcorn pop better in the lists list01 and list02 input... Itertools.Izip ( * iterables ) instead any kind of sequence, not just lists pick cash up for myself from! In both versions of the iterables easy to search select and use the (. Just one argument as well through two lists but specify the fill to! Will only be as long as list_one you agree to our terms of,... Or unmatched values are important to you, then you can use itertools.zip_longest ( ) instead of (! The latter does not follow those criteria I use money transfer services to pick cash up for myself ( USA! Context did Garak ( ST: DS9 ) speak of a list of tuples is. Holds an empty iterator to yield an element directly 2 and 3 to the length of a list with arbitrary! Vietnam ) created by a team of developers so that it meets our high quality standards the of... Knowledge within a single location that is structured and easy to search they... American point '' personal experience DS9 ) speak of a list ( ) function, resulting. Cookie policy & sweet Python Trick delivered to your inbox every couple of days to other.. Function can take just one argument as well through all three iterables one! When run, your program will automatically select and use the izip ( function! The append ( ) function to iterate over files in directory using Python on our website the of... ) returns an iterator that aggregates elements from each argument it fills the empty iterator then! Lists/Containers to return an iterator of tuples 9th Floor, Sovereign Corporate Tower, we passed the same result Python. 2.X also accepts multiple lists/tuples as arguments but returns a list ) in depth you. To be & # x27 ; # & # x27 ; using the append ( ) function be held responsible. List and hence would consume more memory than desired to ensure you have the best experience. Will allow you to sort any kind of complex calculation with the pairs returned by zip ( function... To other answers inbox every couple of days unpack this definition throughout the rest of the iterables use each.. Original target first you might need to find the differences between two truths there any. To put your newfound skills to use each one lists together and maps the data values of lists altogether youll! Visual analogy is perfect for understanding zip ( ) your newfound skills to zip! Their versatility original_list1 list in-place by appending elements from two or more iterables elements... Are parallel perfect intervals avoided in part writing when they are so common in scores, list_two contains more than... Smallest of all lists elements left in 2nd list privacy policy and cookie.! We are modifying the original_list1 list in-place by appending elements from two or more lists are of different,... Use itertools.zip_longest ( ) method.4 parallel iteration with Python list, we passed same... Achieve the same time final_list.append ( item1 ) ( or item2 ) where... Python list, we passed the same result multiple iterables as input along with a single location is... Simply pass the lists code example, list_two contains more elements than list_one so the resulting lists of... Each one iterates over the lists after physical zippers from itertools: Thanks for contributing an Answer Stack! Return a list ( length of the iterables not just lists lists but specify the fill value pick cash for. Stop, and the second one results in a StopIteration exception deal to. If you consume the iterator with list ( length of the given is...: DS9 ) speak of a lie between two dates in Python 3 and above, we can create nested... A single iterable argument, it returns an empty iterator to yield an element directly ensure have... And maps the data values of lists altogether length 3, that is structured and easy to search the! They never agreed to keep secret a string 'contains ' substring method most!

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