How to remove commas etc from a matrix in python

Question

say ive got a matrix that looks like:

[[0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]

how can i make it on seperate lines:

[[0, 0, 0, 0, 0],
[0, 0, 0, 0, 0],
[0, 0, 0, 0, 0]]

and then remove commas etc:

0 0 0 0 0

And also to make it blank instead of 0's, so that numbers can be put in later, so in the end it will be like:

_ 1 2 _ 1 _ 1

(spaces not underscores)

thanks

Answer 1

#!/usr/bin/env python

m = [[80, 0, 3, 20, 2], [0, 2, 101, 0, 6], [0, 72 ,0, 0, 20]]

def prettify(m):
    for r in m:
        print ' '.join(map(lambda e: '%4s' % e, r)).replace(" 0 ", "   ")

prettify(m)

# => prints ...
# 80         3   20    2
#       2  101         6
#      72             20

Answer 2

This allocates 4 spaces for each number in the matrix. You may have to adjust this depending on your data of course.

This also uses the string format method introduced in Python 2.6. Ask if you'd like to see how to do it the old way.

matrix=[[0, 1, 2, 0, 0], [0, 1, 0, 0, 0], [20, 0, 0, 0, 1]]
for row in matrix:
    data=(str(num) if num else ' ' for num in row])   # This changes 0 to a space
    print(' '.join(['{0:4}'.format(elt) for elt in data]))

yields

     1    2             
     1                  
20                  1   

Answer 3

Here is a shorter version of ~untubu's answer

M = [[0, 1, 2, 0, 0], [0, 1, 0, 0, 0], [20, 0, 0, 0, 1]]
for row in M:
    print " ".join('{0:4}'.format(i or " ") for i in row)

Answer 4

This answer also calculates the appropriate field length, instead of guessing 4 :)

def pretty_print(matrix):
  matrix = [[str(x) if x else "" for x in row] for row in matrix]
  field_length = max(len(x) for row in matrix for x in row)
  return "\n".join(" ".join("%%%ds" % field_length % x for x in row)
                   for row in matrix)

There is an iteration too much here, so if performance in critical you'll want to do the initial str() pass and field_length calculation in a single non-functional loop.

>>> matrix=[[0, 1, 2, 0, 0], [0, 1, 0, 0, 0], [20, 1, 1, 1, 0.30314]]
>>> print pretty_print(matrix)
              1       2                
              1                        
     20       1       1       1 0.30314
>>> matrix=[[1, 0, 0], [0, 1, 0], [0, 0, 1]]
>>> print pretty_print(matrix)
1    
  1  
    1

Answer 5

def matrix_to_string(matrix, col):
        lines = []
        for e in matrix:
            lines.append(str(["{0:>{1}}".format(str(x), col) for x in e])[1:-1].replace(',','').replace('\'',''))
        pattern = re.compile(r'\b0\b')
        lines = [re.sub(pattern, ' ', e) for e in lines]
        return '\n'.join(lines)

Example:

matrix = [[0,1,0,3],[1,2,3,4],[10,20,30,40]]
print(matrix_to_string(matrix, 2))

Output:

    1     3
 1  2  3  4
10 20 30 40

Answer 6

If you are doing a lot with matrices, I strongly suggest using numpy (3rd party package) matrix. It has a lot of features that are annoying to do with iteration (e.g., scalar multiplication and matrix addition).

http://docs.scipy.org/doc/numpy/reference/generated/numpy.matrix.html

Then, if you want to make "print" output your particular format, just inherit from numpy's matrix and replace the repr and str methods with some of the solutions presented by the others here.

class MyMatrix(numpy.matrix):
   def __repr__(self):
      repr = numpy.matrix.__repr__(self)

      ...

      return pretty_repr

   __str__ = __repr__