CODEWITHSUNDEEP
pythonpython-3.x
W Szum
W Szum

Reputation: 171

Adding Padding to a 2D Array in Python

How can I add padding consisting of zeros to a 2D array (without using any additional modules)?

For example, I have the following grid:

1 0 1 1
0 1 1 0
1 0 0 1
1 0 1 1

I would like the output to be:

0 0 0 0 0 0
0 1 0 1 1 0
0 0 1 1 0 0
0 1 0 0 1 0
0 1 0 1 1 0
0 0 0 0 0 0

I have tried the following code and its working, but I would like to know if there is a better way to achieve this.

def padded_grid(grid):

    gridpadding = []

    extrarow = [0] * (len(grid) + 2)
    gridpadding.append(extrarow)
    for row in grid:
        row.insert(0, 0)
        row.append(0)
        gridpadding.append(row)
    gridpadding.append(extrarow)

    return gridpadding

Upvotes: 1

Views: 885

Answers (2)

jupiterbjy
jupiterbjy

Reputation: 3503

Read question wrong, so you want to set how much padding you want yet I implemented padding single layer. Simply padding multiple iterations would be simplest.

from pprint import pprint


source = [list(range(n, n + 4)) for n in range(4)]
pprint(source, width=41)


def pad_frame_once(src_: list, pad) -> list:
    output = [[pad, *line, pad] for line in src_]
    return [[pad] * len(output[0]), *output, [pad] * len(output[0])]


def pad_grid(src_, padding_size: int, pad=0):
    reference = src_
    for _ in range(padding_size):
        reference = pad_frame_once(reference, pad)

    return reference


pprint(pad_frame_once(source, pad=0))
pprint(pad_grid(source, 3))


[[0, 1, 2, 3],
 [1, 2, 3, 4],
 [2, 3, 4, 5],
 [3, 4, 5, 6]]
[[0, 0, 0, 0, 0, 0],
 [0, 0, 1, 2, 3, 0],
 [0, 1, 2, 3, 4, 0],
 [0, 2, 3, 4, 5, 0],
 [0, 3, 4, 5, 6, 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, 1, 2, 3, 0, 0, 0],
 [0, 0, 0, 1, 2, 3, 4, 0, 0, 0],
 [0, 0, 0, 2, 3, 4, 5, 0, 0, 0],
 [0, 0, 0, 3, 4, 5, 6, 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]]

Process finished with exit code 0

Upvotes: 2

David Erickson
David Erickson

Reputation: 16683

Without any other libraries, you could use the following assuming a 2-d array called l:

l = [[1, 0, 1, 1],
     [0, 1, 1, 0],
     [1, 0, 0, 1],
     [1, 0, 1, 1]]

def padded_grid(grid):
    n = len(grid[0])
    x = [0 for _ in range(n + 2)]
    [lst.append(0) for lst in grid]
    [lst.insert(0, 0) for lst in grid]
    grid.insert(0,x)
    grid.append(x)
    return grid


padded_grid(grid=l)

[[0, 0, 0, 0, 0, 0],
 [0, 1, 0, 1, 1, 0],
 [0, 0, 1, 1, 0, 0],
 [0, 1, 0, 0, 1, 0],
 [0, 1, 0, 1, 1, 0],
 [0, 0, 0, 0, 0, 0]]

Upvotes: 1

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