how to classify a list of lists by elements length?

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I have a list of lists, looks like this :

List=[[1,3],[3,4,7,9],[4,7],[2,4,5,3],[5,7,4]]

I want to classify the list elements according to their length, so the result looks like this:

2ElelmentSublist=[[1,3],[4,7]]
4ElementSublist=[[3,4,7,9],[2,4,5,3]]
....

And so on.

I read a post about itertools.groupby(), But I couldn’t figure out how to apply it in my case. Any pythonic way to do so?

Note: no need to have the result in separate variables,I need a way to know how many types of lengths I have, and a way to reach every group separately.

Thank you in advance.

You can't make lists with dynamic names to be decided at run-time (like your 2ElementSublist or so.)

But you can design a dictionary with keys as length, and values as lists of lists.

Try this:

result = {}
for L in List:
    result.setdefault(len(L), list()).append(L)
print(result)

and you will see

{2: [[1, 3], [4, 7]], 4: [[3, 4, 7, 9], [2, 4, 5, 3]], 3: [[5, 7, 4]]}

.setdefault(k, d) either gives you access to the dictionary value of key k, or initialize with a default value d. And you append each list.

Python, Python | Maximum sum of elements of list in a list of lists. garg_ak0109. Check out this Author's contributed articles. If you like GeeksforGeeks and would like� Each element of the list is temporarily replaced with a “decorated” version that includes the result of the key function applied to the element. The list is sorted based upon the natural order of the keys.

Might not be the most pythonic, but you can call values similar to how you wanted.

x = [[1,3],[3,4,7,9],[4,7],[2,4,5,3],[5,7,4]]
dic = {f"{len(i)}_elelment": [] for i in x}

for i in x:
    dic[f"{len(i)}_elelment"].append(i)


# {'2_elelment': [[1, 3], [4, 7]], 
#  '4_elelment': [[3, 4, 7, 9], [2, 4, 5, 3]], 
#  '3_elelment': [[5, 7, 4]]}

Python : Get number of elements in a list, lists of lists or nested list , It returns the length of object i.e. count of elements in the object. Now let's use this len() function to get the size of a list i.e.. You can employ a nested loop to count number of elements in each sublist of a list>>> a=[[1, 2, 3], [4, 5, 6]] >>> c=0 >>> for x in a: for y in x:

Since you have mentioned you need the list grouped by len and need them in seperate variable I think you will be needing a dict as your final output.

from itertools import groupby, chain
from collections import defaultdict

List=[[1,3],[3,4,7,9],[4,7],[2,4,5,3],[5,7,4]]

res = defaultdict(list)
for _, v in groupby(sorted(List, key=len)):
    l = list(chain(*v))
    res[len(l)].append(l)

# Output : defaultdict(list,
            {2: [[1, 3], [4, 7]],
             3: [[5, 7, 4]],
             4: [[3, 4, 7, 9], [2, 4, 5, 3]]})

Dart Programming - Lists, Dart Programming - Lists - A very commonly used collection in programming is an The memory blocks holding these values are known as elements. Lists can be classified as − The syntax for declaring a fixed length list is given below − If you want the complete list length, then it considers the Nested list as one element. However, you can get the Nested list length using the index value. For example, the below code is finding the length of a nested list [20, 40, 50, 65, 22].

You can try this:

List = [[1,3],[3,4,7,9],[4,7],[2,4,5,3],[5,7,4]]

sizes = set([(len(element)) for element in List])
result = {}
for element in List:
    if len(element) not in result.keys():
        result[len(element)] = []
    result[len(element)].append(element)
print(result)

And result is:

{2: [[1, 3], [4, 7]], 4: [[3, 4, 7, 9], [2, 4, 5, 3]], 3: [[5, 7, 4]]}

class List, Lists are immutable objects, i.e., neither the number of elements in a list nor the an array of those list values classified into the category of the associated key. or $count is greater than or equal to the size of the list, then all elements from the � s : A sequence like object like, list, string, bytes, tuple etc. It returns the length of object i.e. count of elements in the object. Now let’s use this len () function to get the size of a list i.e. listOfElems = ['Hello', 'Ok', 'is', 'Ok', 'test', 'this', 'is', 'a', 'test']

Use groupby by len:

Ex:

from itertools import groupby

lst = [[1,3],[3,4,7,9],[4,7],[2,4,5,3],[5,7,4]]
print( [list(v) for k, v in groupby(sorted(lst, key=len), key=len)] )
#or
print( {k: list(v) for k, v in groupby(sorted(lst, key=len), key=len)} )

Output:

[[[1, 3], [4, 7]], [[5, 7, 4]], [[3, 4, 7, 9], [2, 4, 5, 3]]]
{2: [[1, 3], [4, 7]], 3: [[5, 7, 4]], 4: [[3, 4, 7, 9], [2, 4, 5, 3]]}

rlist package, Provides a set of functions for data manipulation with list objects, including Most functions are designed to be pipeline friendly so that data processing with lists can be list.findi, Find the indices of a number of elements in a list or vector satisfying a list.class, Classify list elments into unique but non-exclusive cases. A Computer Science portal for geeks. It contains well written, well thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Questions.

How to get the size of a list of lists in Python, The size of a list of lists is the total number of elements contained within all lists in count, element: count + len(element) which adds the length of the current list� Astronomers have devised a classification scheme which describes the absorption lines of a spectrum. They have seven categories (OBAFGKM) each of which is subdivided into 10 subclasses. Thus, the spectral sequence includes B8, B9, A0, A1, etc. A traditional mnemonic for the sequence is Oh, Be, A Fine Girl/Guy, Kiss Me!

Elements of Lists—Wolfram Language Documentation, (Part) — parts of lists, resettable with = Nothing — an element automatically removed from lists. MemberQ — test whether an element is a member of a list. You may also like to read various method to loop through each element. You have to read the tutorial on how to loop over each element of a list in Python. Find Length of List. To find the length of the list in Python, you have to use the len() of Python. The function takes one argument to pass which is the list. If you want to print the length in the output, you have to use the Python print statement.

[PDF] Package 'rlist', Each element of the list is expected to be an atomic vector, data.frame, or data. table of the same length. If list elements are also lists, the binding. Each element can be a different type. Create lists using list() or coerce other objects using as.list(). An empty list of the required length can be created using vector() x <-list (1, "a", TRUE, 1 +4i) x ## [[1]] ## [1] 1 ## ## [[2]] ## [1] "a" ## ## [[3]] ## [1] TRUE ## ## [[4]] ## [1] 1+4i x <-vector ("list", length = 5) ## empty list length (x) ## [1] 5

Comments
  • this code worked for me perfect . but today I discovered that some lists returned distorted(their elements order change ) when I sample form them , I want to know if the problem from the code:
  • sorry my comment not completed : I mean the lists element orders get distorted : for example : Lengths=list(result.keys()), LeftLists=result(lengths[0])#( this is to get items of first length), leftListsSample=random.sample(LeftLists). Now I get some lists out of order , for example a list like l=[1,3,4,5] , in the sample it ll be like [4,3,5,1].
  • I think you should post a new question for that.
  • Thank you , I discovered the problem, I sorted lengths using list.sort() instead sorted(list) which leads to mutating the original lists . Python sometimes so confusing .
  • Thank you very much for your help.
  • Thank you, your time and effort is appreciated.
  • Thank you Rakesh, This is another solution.