Grouping together a list in python

Question

I am trying to group the self.L list into groups of five and then reverse both individual groups I want my output to look as follows

    step1.(group the  list into two section of five)

    [[1,3,5,67,8],[90,100,45,67,865]]

    step2.(reverse the numbers within the two groups)

    [[8,67,5,3,1],[865,67,45,100,90]]

The code I have

        class Flip():
    def __init__(self,answer):
        self.Answer = answer
        self.matrix = None
        self.L = [1,3,5,67,8,90,100,45,67,865,]


    def flip(self):
        if self.Answer == 'h':
            def grouping(self):
                for i in range(0, len(self.L), 5):
                   self.matrix.append(self.L[i:i+5])
            print(self.matrix)

if __name__ =='__main__':
    ans = input("Type h for horizontal flip")
    work = Flip(ans)
    work.flip()

When I run the code my output is

    None

Yes, please revise your code and ensure it is all structured appropriately. Also, setting self.matrix = None is going to give you problems based on how you are using it. You seem to want to use this as a list, so just initialize it as one: self.matrix = [] — idjaw
– idjaw, Commented Mar 7, 2016 at 3:16
You define the function grouping inside the flip method (a closure), but 1/ you don't call grouping(), nor do you return any result from grouping. So you just print the still empty matrix. — user707650
– user707650, Commented Mar 7, 2016 at 3:19

Joe T. Boka · Accepted Answer · 2016-03-07 03:42:08Z

1

To create nested lists with 5 elements in each one, you can use list comprehension:

lst = [1,3,5,67,8,90,100,45,67,865]
new_list = [lst[i:i+5] for i in range(0, len(lst), 5)]

Then to reverse the order of the values in the nested lists you can use .reverse()

for elem in new_list:
    elem.reverse()
print (new_list)

Output:

[[8, 67, 5, 3, 1], [865, 67, 45, 100, 90]]

edited Mar 7, 2016 at 3:42

answered Mar 7, 2016 at 3:37

Joe T. Boka

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1 Comment

Burhan Khalid Over a year ago

You can simply reverse in the list comprehension.

Sci Prog · Accepted Answer · 2016-03-07 03:21:31Z

0

Assuming we receive the initial list in the variable L:

L = [1,3,5,67,8,90,100,45,67,865]

L1 = L[0:5]
L2 = L[5:10]
L=[L1,L2]
print (L)
L1.reverse()
L2.reverse()
L=[L1,L2]
print (L)

edited Mar 7, 2016 at 3:21

answered Mar 7, 2016 at 3:16

Sci Prog

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