How to save a python array with numbers of strings to a file that is human readable

Question

I would like to know how to save the array created in this question's answer (by Paul) to a text file.

How do I print an aligned numpy array with (text) row and column labels?

The details are:

a = np.random.rand(5,4)
x = np.array('col1 col2 col3 col4'.split())
y = np.array('row1 row2 row3 row4 row5'.split())
b = numpy.zeros((6,5),object)
b[1:,1:]=a
b[0,1:]=x
b[1:,0]=y
b[0,0]=''
printer = np.vectorize(lambda x:'{0:5}'.format(x,))
print printer(b).astype(object)

[[     col1 col2 col3 col4]
 [row1 0.95 0.71 0.03 0.56]
 [row2 0.56 0.46 0.35 0.90]
 [row3 0.24 0.08 0.29 0.40]
 [row4 0.90 0.44 0.69 0.48]
 [row5 0.27 0.10 0.62 0.04]]

Answer 1

The way you go about it depends on how you intend to access it. Since you want it human readable, the easy solution is to print it to a file. That does make it more difficult to restore from the file though.

f = open(Filename, 'w')
f.write(str(printer(b).astype(object)))
f.flush()
f.close()

Answer 2

I really like to use the repr() and .rjust() functionality of writelines. So let's say I have a Matrix 'mat' (ie an ndarray) where A.shape = (10,2), and would like certain formatting and rounding, I can get a decent, adjusted output by using the following:

mat = numpy.random.rand(10,10)
f = open('myFile','a')
m,n = mat.shape
for i in range(0,m):
    for j in range(0,n):
        f.writelines(repr(round(mat[i,j],4)).rjust(7))
f.writelines('\n')

f.close()