0. changing a 3D list into a 2D list. Define a list lst with some values. Data items are converted to the nearest compatible builtin Python type, via the item function. The following sample code is based on a Stack Overflow post. To learn more, see our tips on writing great answers. David Robinson's answer is right. I don't think this is what the OP wanted.but your answer is the accepted answer. Does Python have a string 'contains' substring method? Why is it better to control a vertical/horizontal than diagonal? Without this exclusion, these types would be separated into individual characters. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. Developers use AI tools, they just dont trust them (Ep. Method 1: Convert a list to a 2d array in python using Numpy In this method, I will use the numpy python package for the conversion of the list to a 2D array. dev. What conjunctive function does "ruat caelum" have in "Fiat justitia, ruat caelum"? To convert this iterator to a list, use list(). You can transpose a two-dimensional list using the built-in function zip(). of 7 runs, 1000 loops each), # 343 ms 2.19 ms per loop (mean std. Like: Is there a way to convert list_string back to a 2d list ?? str_to_int = list (map (int,string_list)) print (str_to_int) Output If you want a list type object, get numpy.ndarray with the values attribute and convert it to list with the tolist() method. [9,2,3,4,2,1,1,1,3,1,0,1], . See the following article for more information on list comprehensions. What's it called when a word that starts with a vowel takes the 'n' from 'an' (the indefinite article) and puts it on the word? 586), Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Testing native, sponsored banner ads on Stack Overflow (starting July 6), Temporary policy: Generative AI (e.g., ChatGPT) is banned. The zip() function returns an iterator that combines multiple iterables such as list and tuple. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Why did CJ Roberts apply the Fourteenth Amendment to Harvard, a private school? While i is less than the length of var_lst: Extract the sublist of var_lst[i] elements starting at index from lst using slicing. I will just start a new thread. dev. Create pandas.DataFrame from the original 2D list and get the transposed object with the T attribute. Can the type 3 SS be obtained using the ANOVA function or an adaptation that is readily available in Mathematica. I know that we can convert any list to a string using str() : yes, but there various forms for sparse matrices. What's it called when a word that starts with a vowel takes the 'n' from 'an' (the indefinite article) and puts it on the word? Space elevator from Earth to Moon with multiple temporary anchors, Equivalent idiom for "When it rains in [a place], it drips in [another place]". Have ideas from programming helped us create new mathematical proofs? This should be the accepted answer. Making statements based on opinion; back them up with references or personal experience. Scottish idiom for people talking too much. How to take large amounts of money away from the party without causing player resentment? Comic about an AI that equips its robot soldiers with spears and swords. Register to vote on and add code examples. Generating X ids on Y offline machines in a short time period without collision. # Python code to convert a 3D list to a 2D list, Input = [[[ 3 ], [ 4 ]], [[ 5 ], [ 6 ]], [[ 7 ], [ 8 ]]], Method # 2: Using a comprehension list to convert a 3D list to a 2D list, Input = [[[ 1 , 1 ], [ 2 , 7 ]], [[ 3 ], [ 4 ]], [[ 6 , 5 ], [ 6 ]]], Output = [elem for twod in Input for elem in twod], Common xlabel/ylabel for matplotlib subplots, Check if one list is a subset of another in Python, How to specify multiple return types using type-hints. of 7 runs, 1 loop each), # 1.11 ms 110 s per loop (mean std. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. How do I make a flat list out of a list of lists? What are the advantages and disadvantages of making types as a first class value? Without numpy ( ndarray.flatten ) one way would be using chain.from_iterable which is an alternate constructor for itertools.chain : Or as another yet Pythonic approach you can use a list comprehension : Another functional approach very suitable for short lists could also be reduce in Python2 and functools.reduce in Python3 (don't use this for long lists): To make it slightly faster you can use operator.add, which is built-in, instead of lambda: A benchmark on @Will's answer that used sum (its fast for short list but not for long list) : For just a list like this, my favourite neat little trick is just to use sum; sum has an optional argument: sum(iterable [, start]), so you can do: this works because the + operator happens to be the concatenation operator for lists, and you've told it that the starting value is [] - an empty list. Define a function flatten_list(lst) that takes a nested list lst as input.2. This is almost what you want, except each element needs to be a list itself. Use ravel() or flatten() to flatten a NumPy array ndarray. Is there an easier way to generate a multiplication table? I missed a huge part of the question. Raw green onions are spicy, but heated green onions are sweet. While sum() is easy to use, it is significantly slower than itertools.chain.from_iterable() or list comprehensions for large data (many inner lists). Approach : Import numpy package. How can I add new array elements at the beginning of an array in JavaScript? You can specify multiple types by a tuple in the second argument of isinstance(). You can flatten a list of lists with itertools.chain.from_iterable(). Looking for advice repairing granite stair tiles. Here are some ways to swap the rows and columns of this two-dimensional list. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Use slicing to split the array at the indices obtained in step 2. How to convert it to a 2D NumPy array? All the methods discussed here will do the job in two steps: Flatten the list, that is, convert the 2D list into a 1D list, and Convert the numpy array into a list of lists using the tolist () method. [[[0], [0], [1], [0], [1], [0], [0]], [[1], [0], [1], [0], [0], [0], [0]]]. First, though, here is a quick overview: 1) Create Sample 2D List 2) Example 1: Transform 2D List to One Dimension Using itertools Module Calculating the cumulative sum takes O(m) time, where m is the length of the variable lengths list. In this article, you'll see a few of the ways in which you can convert a string to a list. "Least Astonishment" and the Mutable Default Argument, Can the type 3 SS be obtained using the ANOVA function or an adaptation that is readily available in Mathematica. Very conflicted :P. Yeah, I'm not sure why this is accepted. international train travel in Europe for European citizens. Developers use AI tools, they just dont trust them (Ep. Method #1: Using simple iteration to convert a 3D list into a 2D list. Convert to numpy.ndarray and transpose with T, Convert to pandas.DataFrame and transpose with T, Convert numpy.ndarray and list to each other, NumPy: Transpose ndarray (swap rows and columns, rearrange axes), Convert pandas.DataFrame, Series and list to each other, zip() in Python: Get elements from multiple lists, Unpack and pass list, tuple, dict to function arguments in Python, Convert list and tuple to each other in Python, Filter (extract/remove) items of a list with filter() in Python, Count elements in a list with collections.Counter in Python, Swap values in a list or values of variables in Python, Use enumerate() and zip() together in Python, Reverse a list, string, tuple in Python (reverse, reversed), Sort a list of dictionaries by the value of the specific key in Python, Get the number of items of a list in Python, Sort a list, string, tuple in Python (sort, sorted), Remove an item from a list in Python (clear, pop, remove, del), Extract and replace elements that meet the conditions of a list of strings in Python, Extract common/non-common/unique elements from multiple lists in Python. Given the 3D list, the challenge is to convert it to a 2D list. Do large language models know what they are talking about? Difference between machine language and machine code, maybe in the C64 community? It then extracts the sublists from the dictionary in the order of var_lst and returns them as a list of lists. Why did Kirk decide to maroon Khan and his people instead of turning them over to Starfleet? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. Short answer: Convert a list of listslet's call it l to a NumPy array by using the standard np.array (l) function. Usually, a dictionary will be the better choice rather than a multi-dimensional list in Python. why? Do I have to spend any movement to do so? To determine if el is iterable, the function uses collections.abc.Iterable. 3. 6. Method #1: Using simple iteration to convert a 3D list into a 2D list. 25 I am a bit new to Python and I want to convert a 1D list to a 2D list, given the width and length of this matrix. convert a string 2d list back to 2d list in python [duplicate]. This works as well, close to what you tried with list: Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. This works even if the inner lists have a different number of elements. @Kasramvd Awesome response! Time Complexity:Converting the list to a numpy array takes O(n) time, where n is the length of the list. Note that the default value of the second argument is 0, so if omitted, an error is raised due to the + operation with int and list. Thanks for your help! Asking for help, clarification, or responding to other answers. rev2023.7.5.43524. While we have used the list and 2d list, the use of 3d list is increasing day by day, mostly in case of web development. The above example is equivalent to the following nested for loop. 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. [1,2,3,4,1,1,5,1,3,1,1,1], . 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. To learn more, see our tips on writing great answers. Is there any political terminology for the leaders who behave like the agents of a bigger power? ), Convert numpy.ndarray and list to each other, Remove/extract duplicate elements from list in Python, Convert a list of strings and a list of numbers to each other in Python, Count elements in a list with collections.Counter in Python, Get the number of items of a list in Python, Unpack and pass list, tuple, dict to function arguments in Python, Sort a list, string, tuple in Python (sort, sorted), Shuffle a list, string, tuple in Python (random.shuffle, sample), Extract and replace elements that meet the conditions of a list of strings in Python. METHOD 5:Using defaultdict: This solution uses a defaultdict to create a dictionary of sublists from a given input list lst and a list of variable lengths var_lst. Does "discord" mean disagreement as the name of an application for online conversation? Pretty tough. But I got confused about how a non-nested list comprehension like, @WeisiZhan List comprehensions of this kind are usually called nested because of the nested. # Python code to convert a 3D list to a 2D list # Initialization input list Input = [ [ [ 3 ], [ 4 ]], [ [ 5 ], [ 6 ]], [ [ 7 ], [ 8 ]]] # Initialize the output list Output = [] # Using iteration for temp in Input : for elem in temp: Output.append (elem) # print out This is the basic approach for creating a 2d list in python. 586), Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Remove last odd number from number list in Python, Iterate over million points to get unique closest point, Python Cartesian Product in a constrained dictonary, Split dictionary of lists into two dicts based on binary values, Create a dictionary from a list of key and multi list of values in Python. Suppose I have a list like this: myList = [1, 2, 3, 4, 5, 6, 7, 8, 9] I want to convert the above list into a 3 x 3 table like below: myList = [ [1,2,3], [4,5,6], [7,8,9]] Use the below lines of code to implement the conversion. How can I convert a 3D list into a 2D list in python? Whereas the strip () method of class string is used to remove spaces or given characters from the beginning and from the end of string. 586), Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Testing native, sponsored banner ads on Stack Overflow (starting July 6), Temporary policy: Generative AI (e.g., ChatGPT) is banned, Parse string run time parameter to 2D list. By passing an empty list [], the + operation of the list concatenates the lists. Can I knock myself prone? Connect and share knowledge within a single location that is structured and easy to search. This requires importing collections. Connect and share knowledge within a single location that is structured and easy to search. Here is what we will cover: An overview of strings and lists How to check the data type of an object Convert a string to a list of individual characters Convert a string to a list of words split () method suntax breakdown Use split () with a separator The approach used in this program is to recursively traverse the given input list and append the elements to the output list. Python | Ways to flatten a 2D list garg_ak0109 Read Discuss Courses Practice Given a 2D list, Write a Python program to convert the given list into a flattened list. Method 1: Using numpy.array (). You can use the following basic syntax to convert a list in Python to a NumPy array: import numpy as np my_list = [1, 2, 3, 4, 5] my_array = np.asarray(my_list) The following examples shows how to use this syntax in practice. How can I get matrix [ [0,1], [2,3]] width =2, length =2 out of the list? How to take large amounts of money away from the party without causing player resentment? How can I convert a list of arrays into one single list? rev2023.7.5.43524. In the following example, the result is converted to a tuple with tuple(). As strings (str) and byte strings (bytes) are iterable, they are excluded from this operation. Basically, is there a function to convert this back to its original form ? List is a common type of data structure in Python. 1 2 3 4 5 6 rows=[] columns=[] for i in range(3): for j in range(3): columns.append (1) rows.append (columns) OUTPUT- [ [1, 1, 1], [1, 1, 1], [1, 1, 1]] Suppose you want to create a 2d list with coordinates as its values. I know that we can convert any list to a string using str() Like: >>> l = [[1,1] , [2,2] , [3,3]] >>> l [[1, 1], [2, 2], [3 . How to install game with dependencies on Linux? Why a kite flying at 1000 feet in "figure-of-eight loops" serves to "multiply the pulling effect of the airflow" on the ship to which it is attached? How can we compare expressive power between two Turing-complete languages? Have ideas from programming helped us create new mathematical proofs? Do large language models know what they are talking about? I have a list looks like this: [ [1,2,3], [1,2], [1,4,5,6,7]] and I want to flatten it into [1,2,3,1,2,1,4,5,6,7] is there a light weight function to do this without using numpy? Method # 1: Using simple iteration to convert a 3D list to a 2D list. (38 answers) Closed 8 years ago. Hmm..Nope I couldnt find any. What's it called when a word that starts with a vowel takes the 'n' from 'an' (the indefinite article) and puts it on the word? Making statements based on opinion; back them up with references or personal experience. Method 1- Using set () The best way to convert list to set in Python is by using the set () function. Either your solution and San Sarai's solution should be accepted. What are the implications of constexpr floating-point math. What are the pros and cons of allowing keywords to be abbreviated? Python3 Input = [ [ [3], [4]], [ [5], [6]], [ [7], [8]]] Output = [] for temp in Input: for elem in temp: Output.append (elem) print("Initial 3d list is") print(Input) print("Converted 2d list is") print(Output) Output: Functions that accept variable length key value pair as arguments, Python - Iterate through list without using the increment variable, Python | Convert list of string to list of list, Python | Convert list of tuples to list of list, Python | Convert List of String List to String List, Print Single and Multiple variable in Python, Python | Set 6 (Command Line and Variable Arguments), Pandas AI: The Generative AI Python Library, Python for Kids - Fun Tutorial to Learn Python Programming, A-143, 9th Floor, Sovereign Corporate Tower, Sector-136, Noida, Uttar Pradesh - 201305, We use cookies to ensure you have the best browsing experience on our website. The best answers are voted up and rise to the top, Not the answer you're looking for? Stack Exchange network consists of 182 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. By using -1, the size of the dimension is automatically calculated. Equivalent idiom for "When it rains in [a place], it drips in [another place]", international train travel in Europe for European citizens, 4 parallel LED's connected on a breadboard. What does the "yield" keyword do in Python? There can be more than one additional dimension to lists in Python. Find centralized, trusted content and collaborate around the technologies you use most. For performance-sensitive tasks, it is better to avoid sum(). So we can modify it to (thanks Tryph!). For example, consider the following list: If you need to convert a one-dimensional ndarray or list to two dimensions, check the following article. See. How do I check whether a file exists without exceptions? Method #2: Using List Comprehension to convert a 3D list into a 2D list, Method #3: Using Reduce and Chain from itertools to convert a 3D list into a 2D list, Time Complexity: O(n)Auxiliary Space: O(n). A two-dimensional array can be represented by a list of lists using the Python built-in list type. Browse other questions tagged, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site. Method 1: Convert String Array to Int array using python map In this method, I will use the Python map () function to achieve the results. Why is it better to control a vertical/horizontal than diagonal? of 7 runs, 100000 loops each), # 35.5 s 1.2 s per loop (mean std. how to give credit for a picture I modified from a scientific article? Putting the whole thing together for 2D arrays I would put all of the above in a function and then go with a dict comprehension that called it, so something like: Thanks for contributing an answer to Code Review Stack Exchange! What are the advantages and disadvantages of making types as a first class value? In the case of the list comprehension above, as with the other methods, only one level can be flattened, and an error is raised if non-iterable objects are included. Method #1: List slicing Python3 from itertools import islice def convert (lst, var_lst): idx = 0 for var_len in var_lst: yield lst [idx : idx + var_len] idx += var_len lst = [1, 2, 3, 4, 5, 6] var_lst = [1, 2, 3] print(list(convert (lst, var_lst))) Output: [ [1], [2, 3], [4, 5, 6]] Time Complexity: O (n), where n is the length of the list Return the resulting list of lists from the function. You can almost get what you want, but with a linear algorithm, doing the following: This is missing the empty lists for items not present in the original lists. Whenever we encounter a nested list, we call the flatten_list function again to flatten it and append the elements to the output list. List it is a common type of data structure in Python. Time Complexity: The time complexity of this solution is O(n), where n is the length of the input list lst. 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