Rotating Arrays in Python

Question

Good afternoon,

May I please get help in solving an array rotation in Python? I wish to convert a 4 x 4 array into a 16 x 1 array. What I'm thinking is that, I would take each row (4 x 1), rotate it (1 x 4), and append each row rotation on each other until I reach 16 x 1. Would anyone know how to do this in Python? Any help would be appreciated, thank you.

I'ts a very bad question if you only ask for an answer and don't show what you have tried... — ikenas
– ikenas, Commented Aug 13, 2020 at 22:31
You have the algorithm steps. Show the coding problem you have. — Prune
– Prune, Commented Aug 13, 2020 at 22:32
Please provide a minimal reproducible example including sample data and code for what you've tried so far. Is this a list of lists, or an actual array, as in numpy? — G. Anderson
– G. Anderson, Commented Aug 13, 2020 at 22:33
Talking of "rotating" the array does not tally with how you then say that the "rotated" arrays are to be combined, because all that you are really doing is flattening the array. Is your input an actual numpy array, or a list of lists? — alani
– alani, Commented Aug 13, 2020 at 22:39
I apologize, it is bad form to not include code where I attempted a solution. Hadrian solved it (see below). Thank you everybody. — gman2020
– gman2020, Commented Aug 13, 2020 at 23:03

foggynight · Accepted Answer · 2020-11-12 04:16:09Z

1

I'm a little unsure of exactly what you're looking for but:

example_arr = [
  [ 1, 2, 3 ],
  [ 4, 5, 6 ],
  [ 7, 8, 9 ]
]

# List Comprehension
new_arr = [ item for sublist in example_arr for item in sublist ]

# Long Form
new_arr = []
for sublist in example_arr:
  for item in sublist:
    new_arr.append(item)

edited Nov 12, 2020 at 4:16

answered Aug 13, 2020 at 22:31

foggynight

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Comments

Hadrian · Accepted Answer · 2020-08-13 22:52:10Z

0

arr = [[0, 1, 2, 3],
    [4, 5, 6, 7],
    [8, 9, 10, 11],
    [12, 13, 14, 15]]
i = 0
new_arr = []
while i < len(arr):
    new_arr += arr[i]
    i += 1
arr = new_arr
del new_arr# no longer needed

answered Aug 13, 2020 at 22:52

Hadrian

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2 Comments

gman2020 Over a year ago

Thank you, the code you provided works if instead of "arr = new_arr", you instead do "arr1 = new_arr". I just made it it's own variable. That solved my problem.

Hadrian Over a year ago

I gues you can use a for loop instead: for segment in arr:

Prashy · Accepted Answer · 2020-08-13 22:52:08Z

0

Is this something you are looking for?

I/P :

[
  [ 0, 1, 2, 3 ],
  [ 4, 5, 6, 7 ],
  [ 8, 9, 10, 11 ],
  [ 12, 13, 14, 15 ],
]

O/P :

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]

You can try this:

my_arr = [
  [ 0, 1, 2, 3 ],
  [ 4, 5, 6, 7 ],
  [ 8, 9, 10, 11 ],
  [ 12, 13, 14, 15 ],
]

new_arr = []
for row in my_arr:
    new_arr.extend(row)

print(new_arr)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]

answered Aug 13, 2020 at 22:52

Prashy

616 bronze badges

1 Comment

gman2020 Over a year ago

Thank you, I found that your code worked as I was hoping for.

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