Trying to flip columns and rows in an array in python. I can print them, but not sure how make them into a new array

Question

Lets say I have a 9x9 2D array

testboard = [
    [7,8,0,4,0,0,1,2,0],
    [6,0,0,0,7,5,0,0,9],
    [0,0,0,6,0,1,0,7,8],
    [0,0,7,0,4,0,2,6,0],
    [0,0,1,0,5,0,9,3,0],
    [9,0,4,0,6,0,0,0,5],
    [0,7,0,3,0,0,0,1,2],
    [1,2,0,0,0,7,4,0,0],
    [0,4,9,2,0,6,0,0,7]
]

I can print the columns with this code:

for i in range(len(testboard)): 
    for j in range(len(testboard)):
        if j == 8: 
            print(str(testboard[j][i]))
        else:  
            print(str(testboard[j][i]) + ", ", end = "")

which prints this:

7,6,0,0,0,9,0,1,0
8,0,0,0,0,0,7,2,4
0,0,0,7,1,4,0,0,9
4,0,6,0,0,0,3,0,2
0,7,0,4,5,6,0,0,0
0,5,1,0,0,0,0,7,6
1,0,0,2,9,0,0,4,0
2,0,7,6,3,0,1,0,0
0,9,8,0,0,5,2,0,7

However, I would like to put these columns into a new array, of lists. How could I get these into a new array?

Google something like "Python transpose matrix" - flipping rows and columns is called "transposing the matrix" — ForceBru
– ForceBru, Commented Jan 6, 2021 at 19:01

mCoding · Accepted Answer · 2021-01-06 19:10:31Z

1

You were pretty close with your printing, you just need to make a new list,

new = []
for i in range(len(testboard)):
    new.append([])
    for j in range(len(testboard)):
        new[i].append(testboard[j][i])

answered Jan 6, 2021 at 19:10

mCoding

4,9191 gold badge8 silver badges12 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

laleydecamote Over a year ago

Ahh thanks! The new[i] was the part that I was missing

jaykip · Accepted Answer · 2021-01-06 19:11:14Z

0

Try something like testboard = [[testboard[j][i] for j in range(size)] for i in range(size)] to generate a new list where size is the length of the array (9 in your case).

answered Jan 6, 2021 at 19:11

jaykip

466 bronze badges

Comments

DarQ · Accepted Answer · 2021-01-06 19:27:24Z

0

I suppose you are trying to implement the transpose function from scratch; refraining from using numpy.

one way to do is to initialize another array with the shape of the transposed array.

transposed_array = [[0, 0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0, 0]]

and then setting each 0 with its corresponding value in the loop:

for i in range(len(testboard)): 
    for j in range(len(testboard)):
        transposed_array[i][j] = testboard[j][i]

answered Jan 6, 2021 at 19:27

DarQ

1029 bronze badges

Collectives™ on Stack Overflow

Trying to flip columns and rows in an array in python. I can print them, but not sure how make them into a new array

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related