Question

Is there any elegant way to exploit the correct spacing feature of print numpy.array to get a 2D array, with proper labels, that aligns properly? For example, given an array with 4 rows and 5 columns, how can I provide the array and appropriately sized lists corresponding to the row and header columns to generate some output that looks like this?

      A   B   C   D   E
Z [[ 85  86  87  88  89]
Y  [ 90 191 192  93  94]
X  [ 95  96  97  98  99]
W  [100 101 102 103 104]]

If I naively try:

import numpy
x = numpy.array([[85, 86, 87, 88, 89], \
                 [90, 191, 192, 93, 94], \
                 [95, 96, 97, 98, 99], \
                 [100,101,102,103,104]])

row_labels = ['Z', 'Y', 'X', 'W']


print "     A   B   C   D   E"
for row, row_index in enumerate(x):
    print row_labels[row_index], row

I get:

      A   B   C   D   E
Z  [85  86  87  88  89]
Y  [90 191 192  93  94]
X  [95  96  97  98  99]
W  [100 101 102 103 104]

Is there any way i can get things to line up intelligently? I am definitely open to using any other library if there is a better way to solve my problem.

Answer 1

Assuming all matrix numbers have at most 3 digits, you could replace the last part with this:

print "     A   B   C   D   E"
for row_label, row in zip(row_labels, x):
    print '%s [%s]' % (row_label, ' '.join('%03s' % i for i in row))

Which outputs:

     A   B   C   D   E
Z [ 85  86  87  88  89]
Y [ 90 191 192  93  94]
X [ 95  96  97  98  99]
W [100 101 102 103 104]

Formatting with '%03s' results in a string of length 3 with left padding (using spaces). Use '%04s' for length 4 and so on. The full format string syntax is explained in the Python documentation.