Printing boolean numpy array without separators-CodePudding

I would like to print this array:

a = np.array([[0, 1, 0, 0], [1, 1, 1, 1], [0, 0, 0, 0], [0, 0, 0, 0]], dtype=bool)

.8..
8888
....
....

without iterating over each element in a double loop. A terse function like this one:

def showGrid(g):
  print(np.vectorize(lambda x: '8' if x else '.')(g))

but without standard separators:

[['.' '8' '.' '.']
 ['8' '8' '8' '8']
 ['.' '.' '.' '.']
 ['.' '.' '.' '.']]

I couldn't find a way to make np.set_printoptions drop the standard numpy array formatting separators. Is that possible? If not, pointers to any relevant numpy trickery would be appreciated.

CodePudding user response：

First, use np.where to optimize your current code, which is the same and faster than the function wrapped with np.vectorize:

>>> np.where(a, '8', '.')
array([['.', '8', '.', '.'],
       ['8', '8', '8', '8'],
       ['.', '.', '.', '.'],
       ['.', '.', '.', '.']], dtype='<U1')

To concatenate the characters in each line, I prefer to use ndarray.view, which will create a view at a very low cost. It treats all characters in each line as a string with a length of 4:

>>> np.where(a, '8', '.').view('<U4')
array([['.8..'],
       ['8888'],
       ['....'],
       ['....']], dtype='<U4')

Then use ndarray.ravel() or ndarray.flat to unpack the flat results into the print function, with the newline character as the separator:

>>> print(*np.where(a, '8', '.').view('<U4').flat, sep='\n')
.8..
8888
....
....

Or use str.join to get the complete string:

>>> print('\n'.join(np.where(a, '8', '.').view('<U4').flat))
.8..
8888
....
....