Adding Header to Numpy array

Question

I have an array I would like to add a header for.

This is what i have now:

0.0,1.630000e+01,1.990000e+01,1.840000e+01
1.0,1.630000e+01,1.990000e+01,1.840000e+01
2.0,1.630000e+01,1.990000e+01,1.840000e+01

This is what i want:

SP,1,2,3
0.0,1.630000e+01,1.990000e+01,1.840000e+01
1.0,1.630000e+01,1.990000e+01,1.840000e+01
2.0,1.630000e+01,1.990000e+01,1.840000e+01

Notes: "SP" will always be 1st followed by the numbering of the columns which may vary

here is my existing code:

fmt = ",".join(["%s"] + ["%10.6e"] * (my_array.shape[1]-1))

np.savetxt('final.csv', my_array, fmt=fmt,delimiter=",")

You already have an answer here, why asking again ?

Pierre GM
– Pierre GM

2012-09-01 11:28:07 +00:00
Commented Sep 1, 2012 at 11:28 — Pierre GM
– Pierre GM, Commented Sep 1, 2012 at 11:28

makhlaghi · Accepted Answer · 2013-05-13 10:40:01Z

45

Ever since Numpy 1.7.0, three parameters have been added to numpy.savetxt for exactly this purpose: header, footer and comments. So the code to do as you wanted can easily be written as:

import numpy
a = numpy.array([[0.0,1.630000e+01,1.990000e+01,1.840000e+01],
                 [1.0,1.630000e+01,1.990000e+01,1.840000e+01],
                 [2.0,1.630000e+01,1.990000e+01,1.840000e+01]])
fmt = ",".join(["%s"] + ["%10.6e"] * (a.shape[1]-1))
numpy.savetxt("temp", a, fmt=fmt, header="SP,1,2,3", comments='')

answered May 13, 2013 at 10:40

makhlaghi

4,0266 gold badges30 silver badges35 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

user4815162342 · Accepted Answer · 2017-10-03 09:31:16Z

17

Note: this answer was written for an older version of numpy, relevant when the question was written. With modern numpy, makhlaghi's answer provides a more elegant solution.

Since numpy.savetxt can also write to file objects, you can open the file youself and write your header before the data:

import numpy
a = numpy.array([[0.0,1.630000e+01,1.990000e+01,1.840000e+01],
                 [1.0,1.630000e+01,1.990000e+01,1.840000e+01],
                 [2.0,1.630000e+01,1.990000e+01,1.840000e+01]])
fmt = ",".join(["%s"] + ["%10.6e"] * (a.shape[1]-1))

# numpy.savetxt, at least as of numpy 1.6.2, writes bytes
# to file, which doesn't work with a file open in text mode.  To
# work around this deficiency, open the file in binary mode, and
# write out the header as bytes.
with open('final.csv', 'wb') as f:
  f.write(b'SP,1,2,3\n')
  #f.write(bytes("SP,"+lists+"\n","UTF-8"))
  #Used this line for a variable list of numbers
  numpy.savetxt(f, a, fmt=fmt, delimiter=",")

edited Oct 3, 2017 at 9:31

answered Sep 1, 2012 at 7:27

user4815162342

159k22 gold badges347 silver badges417 bronze badges

2 Comments

Eric Escobar Over a year ago

Using this code i get the following error: File "C:\Python32\lib\site-packages\numpy\lib\npyio.py", line 1009, in savetxt fh.write(asbytes(format % tuple(row) + newline)) TypeError: must be str, not bytes @user4815162342

user4815162342 Over a year ago

I've now corrected the answer to work in Python 3, tested with Python 3.2.3.

fgoudra · Accepted Answer · 2022-07-08 14:40:30Z

0

It is also possible to save other things than numpy arrays to file using the savez or savez_compressed functions. Using load function you can retrieve all data like it was pickled like a dict.

import numpy as np

np.savez("filename.npz", array_to_save=np.array([0.0, 0.0]), header="Some header")

data = np.load("filename.npz")
array = data["array_to_save"]
header = str(data["header"])

answered Jul 8, 2022 at 14:40

fgoudra

9211 gold badge11 silver badges30 bronze badges

Collectives™ on Stack Overflow

Adding Header to Numpy array

3 Answers 3

Comments

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related