printing an array in python columnwise

Question

I am trying to add an array like this given below

#       N                     Mn                 Fe                x              x2
3.94870000e+01      -1.22950000e-07     -1.65130000e-05     6.40000000e-01      0.00000000e+00
3.95040000e+01      -9.38580000e-07     -1.63070000e-05     6.41000000e-01      0.00000000e+00
3.95130000e+01      -1.67100000e-06     -1.59280000e-05     6.42000000e-01      0.00000000e+00
3.95230000e+01      -2.29230000e-06     -1.53800000e-05     6.43000000e-01      0.00000000e+00

The code I have managed to write do add the column Mn and Fe, but not yet managed to write it in column as:

# N      Mn    Fe  Res

The code that I have written is:

#!/usr/bin/env python3
# encoding: utf-8

import numpy as np

inp = "ec.dat"
out = "ec2.dat"


N, Mn, Fe, x, x2 = np.loadtxt(inp, unpack=True)
res = Mn+Fe
print(N, res)
# with open("ec2.dat", 'a') as outfile:

Will anyone kindly help me in writing the table properly? Regards,

EDIT @Paul, Thanks. The complete code is now:

#!/usr/bin/env python3
# encoding: utf-8

import numpy as np

inp = "ec.dat"
out = "ec2.dat"


N, Mn, Fe, x, x2 = np.loadtxt(inp, unpack=True)
res = Mn+Fe
with open("ec2.dat", "w") as of:
    for n, mn, fe, res in zip(N, Mn, Fe, res):
        s = "%e %e\n" % (n, res)
        of.write(s)

So your primary goal is to output the data in that format? i.e. print to screen? Or to a file? Have you looked at pythons string formatting yet? What else have you tried? You could iterate over the numpy arrays simultaneously and create lines one at a time for instance. — Paul Seeb
– Paul Seeb, Commented Aug 6, 2014 at 14:13
print it to a file just in the same way my input file is, with the res column added — BaRud
– BaRud, Commented Aug 6, 2014 at 14:14
If you want the other terms you can also do s = "%e %e %e %e\n" % (n, mn, fe, res) and the spacing between each "%e" is entirely adjustable if you need to change your formatting. — Paul Seeb
– Paul Seeb, Commented Aug 6, 2014 at 19:33

Paul Seeb · Accepted Answer · 2014-08-06 14:23:29Z

2

Rather than put the answer together, I will show you individual parts so you can work through this yourself.

To iterate over multiple numpy arrays simultaneously, you could do the following:

for n, mn, fe, result in zip(N, Mn, Fe, res):
    print "" + str(n) + " " + str(mn) +" " + str(fe) + " " + str(result)

However, to perform the desired formatting, you should use string specifiers: https://docs.python.org/2/library/string.html#format-specification-mini-language

One example would be something like

v = 1000.526
s = "%e   %e\n" % (10.25, v)
print s

writing to a file is as simple as doing:

s = "Here is a line I will write to my file\n"
with open("ec2.dat", 'a') as outfile:
    outfile.write(s)

Linking these things together you should be able to print your desired output to the screen or a file.

answered Aug 6, 2014 at 14:23

Paul Seeb

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