Question

Okay this is probably a really dumb question, however it’s really starting to hurt. I have a numpy matrix, and basically I print it out row by row. However I want to make each row be formatted and separated properly.

>>> arr = numpy.matrix([[x for x in range(5)] for y in range(5)])
>>> arr
matrix([[0, 1, 2, 3, 4],
        [0, 1, 2, 3, 4],
        [0, 1, 2, 3, 4],
        [0, 1, 2, 3, 4],
        [0, 1, 2, 3, 4]])

Lets say i want to print the first row, and add a ‘|’ between each element:

>>> '|'.join(map(str, arr[0,]))
'[[0 1 2 3 4]]'

Err…

>>> '|'.join(map(lambda x: str(x[0]), arr[0]))
'[[0 1 2 3 4]]'

I am really confused by this behavior why does it do this?

Answer 1

arr is returned as a matrix type, which may not be an iterable object that plays nicely with join.

You could convert arr to a list with tolist() and then perform your join.

>>> a = arr.tolist() # now you can manipulate the list.
>>> for i in a:
 '|'.join(map(str,i))    

'0|1|2|3|4'
'0|1|2|3|4'
'0|1|2|3|4'
'0|1|2|3|4'
'0|1|2|3|4'

Or with an array using numpy.asarry for that matter

>>> arr = numpy.matrix([[x for x in range(5)] for y in range(5)])
>>> ele = numpy.asarray(arr)
>>> '|'.join(map(str,ele[0,]))
'0|1|2|3|4' # as per your example.