How to print Numpy arrays without any extra notation (square brackets [ ] and spaces between elements)?

Question

I have a 2-dimensional numpy array that looks like this:

[[a b c]
 [d e f]
 [g h i]]

I'd like to print it without any of the default notational fluff that typically comes with arrays; namely the [, ] and the spaces between the elements. Something like this:

abc
def
ghi

Is it possible to do such a thing (without a trivial and possibly expensive Python loop, of course)?

I have looked at numpy.set_printoptions but it looks like it only sets presentational options for how elements are displayed, not the characters in between.

Edit: The elements in the array have a string representation that can be anything, including [, ] and whitespace. Minimal example of how to build such an array:

class custom(object):
    def __repr__(self):
        return 'a'
a = numpy.empty((5, 5), custom)
a.fill(custom())
print a

Just to be clear: your custom repr includes a terminal `.` that you want to get rid of, but might include others that you don't? I'm not sure I understand what you want to strip. — DSM, Mar 22 '12 at 20:18
My bad, this was due to me editing the representation by hand. My original question used a numpy array of regular numbers, for which there is a `.` after each number used as delimiter (or as decimal separator, not sure). Later, I edited my question to reflect that the data type of the array was not necessarily numerical, and forgot to change the delimiter accordingly. Edited again. — Etienne Perot, Mar 22 '12 at 20:28
Subset: only remove `[]`: http://stackoverflow.com/questions/9360103/how-to-print-a-numpy-array-without-brackets/42046765#42046765 — Ciro Santilli OurBigBook.com, Feb 04 '17 at 23:18

score 10 · Accepted Answer · answered Mar 22 '12 at 20:29

While this pretty much amounts to a loop, I think this is probably the best you're going to get. Generally the join string method is pretty fast.

>>> a = np.array([[1,2,3],[2,4,6],[-1,-2,-3]])
>>> print '\n'.join(''.join(str(cell) for cell in row) for row in a)
123
246
-1-2-3

I think at this point you'd probably be best off implementing something and measuring how long it takes. My guess is that the slowest part of the code will be actually printing to console, not joining the strings together.

Well, I guess that means there is no "numpy way" to do it. Thanks anyway — Etienne Perot, Mar 22 '12 at 22:16

score 8 · Answer 2 · answered May 30 '15 at 08:51

8

np.savetxt(sys.stdout.buffer, a, fmt='%s', delimiter='')

answered May 30 '15 at 08:51

panda-34

4,089
20
25

Do you really need `.buffer` at `sys.stdout.buffer`? – Ciro Santilli OurBigBook.com Feb 04 '17 at 23:18
1

@CiroSantilli烏坎事件2016六四事件法轮功, savetxt writes bytestring and so expects a binary file – panda-34 Feb 05 '17 at 17:52
Does exactly what the question asks and does so efficiently from within NumPy. Using just `sys.stdout` also works. – Teun M. Jan 22 '23 at 10:04

score 1 · Answer 3 · answered Mar 22 '12 at 20:08

1

>>> import numpy    
>>> a = numpy.array([[ 1.0,  2,  3], [ 4,  5,  6], [ 7,  8,  9]])
>>> print str(a).replace(' ','').replace('.','').replace('[','').replace(']','')
123
456
789

answered Mar 22 '12 at 20:08

fraxel

34,470
11
98
102

+1 because it does answer the question I asked, but the real array in question uses a custom data type for which the string representation can be anything, including spaces and brackets. Edited the question to reflect this – Etienne Perot Mar 22 '12 at 20:11
@Etienne Perot - back to the drawing board! – fraxel Mar 22 '12 at 20:22

score 0 · Answer 4 · edited May 09 '17 at 14:50

0

It's pretty simple, if a is your array just do this:

print(re.sub('[ ]+', ' ', re.sub(' *[\\[\\]] *', '', np.array_str(a))))

edited May 09 '17 at 14:50

arco444

22,002
12
63
67

answered May 09 '17 at 14:41

Manoj Narang

1

How to print Numpy arrays without any extra notation (square brackets [ ] and spaces between elements)?

4 Answers4