Introduction to NumPy and Matplotlib
Chapter 8: NumPy recap and exercises
Checkerboard pattern
A final mega-challenge question!
Challenge #5
Using as few lines of code as possible, create an 8 \times 8 NumPy array with a checkerboard pattern:
[
[0, 1, 0, 1, 0, 1, 0, 1],
[1, 0, 1, 0, 1, 0, 1, 0],
[0, 1, 0, 1, 0, 1, 0, 1],
[1, 0, 1, 0, 1, 0, 1, 0],
[0, 1, 0, 1, 0, 1, 0, 1],
[1, 0, 1, 0, 1, 0, 1, 0],
[0, 1, 0, 1, 0, 1, 0, 1],
[1, 0, 1, 0, 1, 0, 1, 0]
]
There are potentially many solutions to this! You can even try generalising the board to N \times N for any N if you are up for it!
There are many solutions for these question!
Here is one that uses list comprehension to create different 2D off-diagonal arrays and then adds them all up.
n = 8
checkerboard = np.sum(np.dstack([
np.eye(n, k=k, dtype=int)
for k in np.arange(-(n+1), n+1, 2)]
), axis=2)
Here is another clever one. It uses np.indices to obtain the (row, col) indices for a grid, and then adds up the indices of each row+col. If the row+col is even, then it should display 0 (e.g. (0,0), (0,2)). Otherwise, display 1.
n = 8
checkerboard = np.indices((n, n)).sum(axis=0) % 2
The next solution uses np.tile() to tile up [[0 1],[1 0]]. It only works for an even number of rows/cols though!
np.array(np.tile(np.eye(2) == 0, (4, 4)), dtype=int)
This following solution uses just pure Python (except for creating the np.array). It also only works for an even number of rows/cols!
x = np.array([[0, 1] * 4, [1, 0] * 4] * 4)
This stackoverflow page has even more solutions! Choose your favourite!