How do I convert the rows of a matrix to columns in Python without NumPy?

Question

I am working on a Sudoku Solver in Python, and I need to create functions in it. One of them checks the Sudoku Matrix and returns the number of rows in it that contains a repeating number.

def findRepeatsInColumn(matrix):
    numRepeats = 0
    for row in matrix:
        safeChars=['[', ']', '/']
        usedChars=[]
        for char in str(row):
            if char in usedChars and char not in safeChars:
                numRepeats += 1
                break
            else:
                usedChars.append(char)
    return numRepeats

If I pass a matrix [[1, 1, 1], [2, 2, 2], [3, 3, 3]] to it, it functions fine and gives me the output 3, but for checking all columns for repeated numbers, I need to convert the rows into columns, which means I would need something like: Input: [[1, 1, 1], [2, 2, 2], [3, 3, 3]] Output: [[1, 2, 3], [1, 2, 3], [1, 2, 3]] Any thoughts on how I could do this without NumPy?

Suggestion 2: use [[1, 1, 1], [2, 2, 2], [3, 3, 3]] instead of [[111], [222], [333]] — norok2
– norok2, Commented Apr 4, 2020 at 8:54
@AngusTay I hardly believe it is easy to vectorize the operations you would need to implement for a sudoku solver. Unless one plans on using Numba. — norok2
– norok2, Commented Apr 4, 2020 at 8:55
@Angus, transpose in numpy is easy, but iterations like this are slower. Conversion to/from arrays is also slow. — hpaulj
– hpaulj, Commented Apr 4, 2020 at 14:35

Susmit Agrawal · Accepted Answer · 2020-04-04 08:50:50Z

1

One simple way is to make use of zip and *:

>>> ip = [[1, 1, 1], [2, 2, 2], [3, 3, 3]]

>>> print(list(zip(*ip)))
[(1, 2, 3), (1, 2, 3), (1, 2, 3)]

answered Apr 4, 2020 at 8:50

Susmit Agrawal

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Dharman · Accepted Answer · 2020-04-04 13:16:48Z

1

Suppose you have a matrix named m

transposed = zip(*m)

edited Apr 4, 2020 at 13:16

Dharman♦

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answered Apr 4, 2020 at 8:51

yiping wang

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kederrac · Accepted Answer · 2020-04-04 09:05:46Z

0

if your input isnumpy.array you may use the transpose:

i = np.array([[1,1,1], [2,2,2], [3,3,3]])
print(i.T)

output:

[[1 2 3]
 [1 2 3]
 [1 2 3]]

or you could use:

list(map(list, zip(*i)))

edited Apr 4, 2020 at 9:05

answered Apr 4, 2020 at 9:00

kederrac

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