How to make a checkerboard in numpy?

Question

I\'m using numpy to initialize a pixel array to a gray checkerboard (the classic representation for \"no pixels\", or transparent). It seems like there ought to be a whizzy

Answer 1

this ought to do it

any size checkerboard you want (just pass in width and height, as w, h); also i have hard-coded cell height/width to 1, though of course this could also be parameterized so that an arbitrary value is passed in:

>>> import numpy as NP

>>> def build_checkerboard(w, h) :
      re = NP.r_[ w*[0,1] ]              # even-numbered rows
      ro = NP.r_[ w*[1,0] ]              # odd-numbered rows
      return NP.row_stack(h*(re, ro))


>>> checkerboard = build_checkerboard(5, 5)

>>> checkerboard
 Out[3]: array([[0, 1, 0, 1, 0, 1, 0, 1, 0, 1],
               [1, 0, 1, 0, 1, 0, 1, 0, 1, 0],
               [0, 1, 0, 1, 0, 1, 0, 1, 0, 1],
               [1, 0, 1, 0, 1, 0, 1, 0, 1, 0],
               [0, 1, 0, 1, 0, 1, 0, 1, 0, 1],
               [1, 0, 1, 0, 1, 0, 1, 0, 1, 0],
               [0, 1, 0, 1, 0, 1, 0, 1, 0, 1],
               [1, 0, 1, 0, 1, 0, 1, 0, 1, 0],
               [0, 1, 0, 1, 0, 1, 0, 1, 0, 1],
               [1, 0, 1, 0, 1, 0, 1, 0, 1, 0]])

with this 2D array, it's simple to render an image of a checkerboard, like so:

>>> import matplotlib.pyplot as PLT

>>> fig, ax = PLT.subplots()
>>> ax.imshow(checkerboard, cmap=PLT.cm.gray, interpolation='nearest')
>>> PLT.show()

Answer 2

n = int(input())
import numpy as np
m=int(n/2)
a=np.array(([0,1]*m+[1,0]*m)*m).reshape((n,n))

print (a)

So if input is n = 4 then output would be like:

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

Answer 3

Using tile function :

import numpy as np
n = int(input())
x = np.tile(arr,(n,n//2))
x[1::2, 0::2] = 1
x[0::2, 1::2] = 1
print(x)

Answer 4

I'd use the Kronecker product kron:

np.kron([[1, 0] * 4, [0, 1] * 4] * 4, np.ones((10, 10)))

The checkerboard in this example has 2*4=8 fields of size 10x10 in each direction.

Answer 5

Can't you use hstack and vstack? See here. Like this:

>>> import numpy as np
>>> b = np.array([0]*4)
>>> b.shape = (2,2)
>>> w = b + 0xAA
>>> r1 = np.hstack((b,w,b,w,b,w,b))
>>> r2 = np.hstack((w,b,w,b,w,b,w))
>>> board = np.vstack((r1,r2,r1,r2,r1,r2,r1))

Answer 6

For those wanting arbitrarily sized squares/rectangles:

import numpy as np
# if you want X squares per axis, do squaresize=[i//X for i in boardsize]
def checkerboard(boardsize, squaresize):
    return np.fromfunction(lambda i, j: (i//squaresize[0])%2 != (j//squaresize[1])%2, boardsize).astype(int)

print(checkerboard((10,15), (2,3)))
[[0 0 0 1 1 1 0 0 0 1 1 1 0 0 0]
 [0 0 0 1 1 1 0 0 0 1 1 1 0 0 0]
 [1 1 1 0 0 0 1 1 1 0 0 0 1 1 1]
 [1 1 1 0 0 0 1 1 1 0 0 0 1 1 1]
 [0 0 0 1 1 1 0 0 0 1 1 1 0 0 0]
 [0 0 0 1 1 1 0 0 0 1 1 1 0 0 0]
 [1 1 1 0 0 0 1 1 1 0 0 0 1 1 1]
 [1 1 1 0 0 0 1 1 1 0 0 0 1 1 1]
 [0 0 0 1 1 1 0 0 0 1 1 1 0 0 0]
 [0 0 0 1 1 1 0 0 0 1 1 1 0 0 0]]