python create list from list with condition

This is 3 times faster than the method proposed by @j1-lee if speed is a consideration. I've got this block of code in a real Django function. The potentially IndexError-prone condition i[6]!="H" will only be evaluated if the string is of length 7, ensuring that you're not going to get this error. Making statements based on opinion; back them up with references or personal experience. We can also perform transformations on nested lists using comprehensions. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. WebBelow, we will create a list with range function and a if condition. It' s not needed or at least will be ignored. And voila! One of the languages most distinctive features is the list comprehension, which you can use to create powerful functionality within a single line of code.However, many developers struggle to fully leverage the more advanced features If you don't want those strings that end with H in the 7th position irrespective of their length, you should redo your logical expression: As others have pointed out, len("CCC-A-H") == 7 and python employs short-circuit evaluation on boolean operations. WebCreate a List: thislist = ["apple", "banana", "cherry"] print(thislist) Try it Yourself List Items List items are ordered, changeable, and allow duplicate values. Why the ant on rubber rope paradox does not work in our universe or de Sitter universe? However, I do not want to remove the entries now. You need to reference the index, and not the item itself: Thanks for contributing an answer to Stack Overflow! How do you manage the impact of deep immersion in RPGs on players' real-life? Lets dive into list comprehensions with conditional statements. We use the function within the list comprehension by calling square(num) on each element num in the numbers list. Happy coding! Not the answer you're looking for? Creating list from list Specify a PostgreSQL field name with a dash in its name in ogr2ogr, Replace a column/row of a matrix under a condition by a random number. You can explore and leverage list comprehensions in your projects, as they can greatly simplify your code and make it more elegant. Can somebody be charged for having another person physically assault someone for them? This allows us to selectively include or exclude elements from the new list based on specific conditions. Here, willl check the numbers from 0 to 9 and if these numbers are smaller than 8 and higher than 2, we will create a list with these numbers. We might try to exploit it using: but this still is a restriction for how you describe your logic, still has the nasty side effect of evaluating all values no matter the condition (unless you throw in a ton of lambdas), and I can't really see it as an improvement over what we've started with. What would naval warfare look like if Dreadnaughts never came to be? Line-breaking equations in a tabular environment. 0. Web1 I would like to loop in all rows and generate a list of a list based on a condition from two columns. I know is a dirty coding and I'm quite sure I can do better, but for now I have serious issues combining various list comprehension routines. A car dealership sent a 8300 form after I paid $10k in cash for a car. How can i solve this problem? Share Follow Can someone help me understand the intuition behind the query, key and value matrices in the transformer architecture? Example 1: Creating a list in Python Python3 List = [] print("Blank List: ") print(List) List = [10, 20, 14] print("\nList of numbers: ") print(List) List = ["Geeks", "For", "Geeks"] print("\nList Items: ") print(List[0]) print(List[2]) Output Blank List: [] List of numbers: [10, 20, 14] List Items: Geeks Geeks By combining conditional expressions and the count() method, you can create a compact solution to count occurrences without the need for explicit loops. You can also mix objects of different types within the same list, although list elements often share the same type. I read in some XML data using ElementTree and after parsing it, I iterate through the tree and put all of the tags in a list called tags and their values in a list called vals.. list = [x for x in range (10) if (x < 8) & (x > 2) ] We achieve this by adding the conditions num % 2 == 0 and num % 3 == 0 after the iteration. 2. Asking for help, clarification, or responding to other answers. Conditionally create list of lists. To create a nested list using comprehensions, we can simply have another list comprehension inside the main one. Python : Check if all elements in a List are same or matches a condition ; Python : Check if Connect and share knowledge within a single location that is structured and easy to search. Is there an equivalent of the Harvard sentences for Japanese? If we were to rewrite this using if elif else constructs, it would look something like this: This would make the list comprehension look like: The reason your code doesn't raise an IndexError is because all of your data items are either 5 or 7 elements long. Is saying "dot com" a valid clue for Codenames. Under the hood, list comprehensions are optimized by the programming language itself, which can lead to improved performance. Thank you for your assistance! In this case I want to add all words that have the length of 9 to a new list. List comprehensions provide a concise and expressive way to perform operations on lists, while traditional loops, like for loops, are the more traditional and familiar approach. We can also access methods on elements directly within list comprehensions. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Lastly, list comprehensions combine the process of iterating over a list and performing an operation into a single line, reducing the chances of introducing bugs or mistakes. Proof that products of vector is a continuous function. Web1 Answer Sorted by: 1 You can append a new sub-list if the output is empty or if the current item is less than the last item in the last sub-list: list_of_lists= [] for i in index: if not list_of_lists or i < list_of_lists [-1] [-1]: list_of_lists.append ( []) list_of_lists [-1].append (i) list_of_lists becomes: What's the DC of a Devourer's "trap essence" attack? What should I do after I found a coding mistake in my masters thesis? Find centralized, trusted content and collaborate around the technologies you use most. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, I am sorry I just updated the num-users. python The end result is that: will return true because len("CCC-A-H") == 7 evaluates to true before "CCC-A-H"[6] != "H" is evaluated. My code did not work, You are right! By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 592), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned. The solution offered by @jpp seems more clean (for my eyes) but thanks man! Using functions and methods within list comprehensions allows us to perform custom operations and transformations on elements in a concise and readable manner. Creating a list of lists in python is a little tricky. Creating list from list in python based on an if condition. My question was not clear enough. Example 2: Get a sublist containing numbers between 70 to 80 from the list. Web20 I want to make a new list from another list of words; when a certain condition of the word is met. Your email address will not be published. How to create a list conditionally? Lets explore some advanced techniques in list comprehension that can take your code to the next level. you can actually write the same condition with Python's truthy semantics, like this, alternatively, you can use filter function with your meetsCondition, like this, Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. from List even_numbers = {num for num in numbers if num % 2 == 0}. I've put a series of conditions and I got this result: Of what condition I need to filter again? Python Does the US have a duty to negotiate the release of detained US citizens in the DPRK? Ordered Could ChatGPT etcetera undermine community by making statements less significant for us? Method 2: Using List Comprehension. Webdef subList (inputList): outputList = [] for element in inputList: if meetsCondition (element): outputList.append (element) return outputList divisibleBySeven = subList (listOfNumbers) Is there a simple way to do this, perhaps with a list comprehension or set () functions, and without the temporary outputList? My ideal output is tags_dict = {'TAG_ONE': [1, 2, 3], 'TAG_TWO': [5, 6]} which I achieved using the code below. Can a creature that "loses indestructible until end of turn" gain indestructible later that turn? rev2023.7.24.43543. Python List Comprehension containing IF Condition Share Follow You can perform various mathematical operations or even apply functions within the expression to get the desired transformation. You can either store a particular data type or mix them. num_users = 3 in the example, but it is 100 in my code, Creating a list of lists based on a conditions, Improving time to first byte: Q&A with Dana Lawson of Netlify, What its like to be on the Python Steering Council (Ep. @Puciek - I dont agree, but in any case the question was updated, so that irrelevant. In a list, you can store objects of any type. In the next section, you'll see how to add items to a list. I have used : resultReal = [y for y in resultVital if not len (y) < 4] to remove all entries that are under the length of 4. Can somebody be charged for having another person physically assault someone for them? What is the smallest audience for a communication that has been deemed capable of defamation? Python List Comprehension containing IF Condition We can perform calculations or transformations on each item in the existing list to create a new list. Well, you can simplify that greatly using collections.defaultdict(list). A Python list comprehension consists of brackets containing the expression, which is executed for each element along with the for loop to iterate over each element in the Python list . store duplicate elements # list with elements of different data types list1 = [1, "Hello", 3.4] # list with duplicate elements list1 = [1, "Hello", 3.4, "Hello", 1] # empty list list3 = [] Proof that products of vector is a continuous function. Making statements based on opinion; back them up with references or personal experience. Connect and share knowledge within a single location that is structured and easy to search. Creating a list of lists in python is a little tricky. python 0. Your email address will not be published. What's the purpose of 1-week, 2-week, 10-week"X-week" (online) professional certificates? Line-breaking equations in a tabular environment. 1 I'm trying to create a new list from another list based on condition: Example 1: Get a sublist containing only odd numbers from list. I am trying something like this: new_list = [x for x in old_list if idx [x] == 3] IndexError: arrays used as indices must be of integer (or boolean) type Heres an example: matrix = [ [x for x in range (1, 4)] for _ in range (3)] Here, we use a nested comprehension to generate a 33 matrix. Despite providing the same result, pay attention to the fact that the former example is almost 2x faster than the latter one. Share Follow What should I do after I found a coding mistake in my masters thesis? What's the DC of a Devourer's "trap essence" attack? Not the answer you're looking for? Python Example 2: Get a sublist containing numbers between 70 to 80 from the list. Python Not the answer you're looking for? Python List Comprehension Syntax newList = [ expression (element) for element in oldList if condition ] I read in some XML data using ElementTree and after parsing it, I iterate through the tree and put all of the tags in a list called tags and their values in a list called vals.. These advanced techniques expand the capabilities of list comprehensions, allowing you to perform complex iterations, apply multiple conditions, and create dictionaries or sets with ease. You can choose any name for this variable, like num, name, or item itself. By using list comprehensions, you think about transforming data, resulting in cleaner and maintainable code. English abbreviation : they're or they're not. If use pandas solution with reshape by DataFrame.stack and aggregate list is possible, but slow: df ['tags'] = df [tags].stack ().groupby (level=0).agg (list).reindex (df.index, fill_value= []) print (df) text acquisition tender opinion \ 0 Quinbrook acquires planned 350 MW project acquisition NaN NaN 1 WebPython is famous for allowing you to write code thats elegant, easy to write, and almost as easy to read as plain English. Web1 I want to create a new_list which will contain only the items of my old_list which satisfy the condition that the index in an array of labels is 3. I'm drawing a blank on how to simplify the code into some sort of list comprehension (or something else). By leveraging the capabilities of list comprehensions, you can write code that is both efficient and readable, making your programming tasks more enjoyable and productive. Creating Method 1: Using filter () method. List List 2. Within my list of tags, there are a few By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. The resulting pairs list contains tuples, where each tuple represents a combination of one number from [1, 2, 3] and one character from [a, b, c]. Example 1: Creating a list in Python Python3 List = [] print("Blank List: ") print(List) List = [10, 20, 14] print("\nList of numbers: ") print(List) List = ["Geeks", "For", "Geeks"] print("\nList Items: ") print(List[0]) print(List[2]) Output Blank List: [] List of numbers: [10, 20, 14] List Items: Geeks Geeks Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, How to return a subset of a list that matches a condition [duplicate]. List comprehensions offer benefits such as improved code performance, support for complex transformations, and the ability to create dictionaries and sets. Find centralized, trusted content and collaborate around the technologies you use most. I am trying my best to explain the problem. Generalise a logarithmic integral related to Zeta function. I don't know if I'm phrasing this in the best way, but essentially I'd like to create a list of lists based on different conditions. Python Program list_1 = [7, 2, 6, 2, 5, 4, 3] list_2 = [ x * x for x in list_1 if (x % 2 == 0) ] print(list_2) Run Code Online Is there a word in English to describe instances where a melody is sung by multiple singers/voices? I would recommend clarifying this question greatly - what kind of data are you getting and what do you expect to get out? How to create and initialize a list The inner comprehension [x for x in range (1, 4)] creates a row with numbers from 1 to 3. Is not listing papers published in predatory journals considered dishonest? Method 2: Using List Comprehension. It allows you to create variable-length and mutable sequences of objects. Method 1: Using filter () method. Python List Comprehension In the next section, you'll see how to add items to a list. As far I can see there is just a small issue: the items starting with '#' are lists in a list. edited: Idx is an array of equal size with my original data which contains labels for them. Sorted by: 1. Which denominations dislike pictures of people? You might find this useful: That is perfect, and precisely what I was looking for. python Despite providing the same result, pay attention to the fact that the former example is almost 2x faster than the latter one. A list can store elements of different types (integer, float, string, etc.) python By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. For instance, if you have 5 lists and you want to create a list of lists from the given lists, you can put them in square brackets as shown in the following python code. minimalistic ext4 filesystem without journal and other advanced features. This allows us to set more complex criteria. Is there a more Pythonic way of phrasing this construct, perhaps that initialises and populates the array in one blow? Solving programming problems using list comprehensions. What is the smallest audience for a communication that has been deemed capable of defamation? Python Web1 I would like to loop in all rows and generate a list of a list based on a condition from two columns. I would remove the numbers between E_time[i] & S_time[I] in the list. Asking for help, clarification, or responding to other answers. What that does: the x in the function holds the list of numbers that has been passed to it, as in list_even(numbers) The list of numbers is passed to the function, which can use that list, which is held in the a local variable, x.
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