Create numpy array from matrix declared inside .m matlab file

Question

A coworker left some data files I want to analyze with Numpy.

Each file is a matlab file, say data.m, and have the following formatting (but with a lot more columns and rows):

values = [-24.92 -23.66 -22.55 ;
-24.77 -23.56 -22.45 ;
-24.54 -23.64 -22.56 ;
];

which is the typical explicit matrix creation syntax used by matlab.

My question is: what would be the most practical way to create a numpy array from these files?

I could think about a "brute force" or a "quick and dirty" solution, but if there would be a more straightforward one, I would much rather use it, like a standard function from numpy or even from another module.

EDIT: I noticed that my files may contain NaN values, so I most probably will adapt the answers given to use numpy.genfromtxt instead of numpy.loadtxt. I plan to include my final code as soon as I have it.

Thanks for any help!

EDIT: I ended up with the following code, where I get everything between [] using regex, and create a numpy array using genfromtxt in order to handle NaN. A shorter solution could be to use fromstring method, which does not need StringIO, but this cannot handle NaN, and my data have NaN :oP

#!/usr/bin/env python
# coding: utf-8

import numpy, re, StringIO

with open('data.m') as f:
    s = re.search('\[(.*)\]', f.read(), re.DOTALL).group(1)
    buf = StringIO.StringIO(s)
    a = numpy.genfromtxt(buf, missing_values='NaN', filling_values=numpy.nan)

Answer 1

Here are a couple options, although neither is built in.

The solution you probably do not find acceptable

This solution probably falls into your "quick and dirty" category, but it helps lead in to the next solution.

Remove the values = [, the last line (];), and globally replace all ; with nothing to get:

-24.92 -23.66 -22.55 
-24.77 -23.56 -22.45 
-24.54 -23.64 -22.56 

Then you can use numpy's loadtxt as follows.

>>> import numpy as np
>>> A = np.loadtxt('data.m')

>>> A
array([[-24.92, -23.66, -22.55],
       [-24.77, -23.56, -22.45],
       [-24.54, -23.64, -22.56]])

A solution you might find acceptable

In this solution, we create a method to coerce the input data into a form that numpy loadtxt likes (the same form as above, actually).

import StringIO
import numpy as np

def convert_m(fname):
    with open(fname, 'r') as fin:
        arrstr = fin.read()
    arrstr = arrstr.split('[', 1)[-1] # remove the content up to the first '['
    arrstr = arrstr.rsplit(']', 1)[0] # remove the content after ']'
    arrstr = arrstr.replace(';', '\n') # replace ';' with newline
    return StringIO.StringIO(arrstr)

Now that we have that, do the following.

>>> np.loadtxt(convert_m('data.m'))
array([[-24.92, -23.66, -22.55],
       [-24.77, -23.56, -22.45],
       [-24.54, -23.64, -22.56]])

Answer 2

You could feed an iterator to np.genfromtxt:

import numpy as np
import re

with open(filename, 'r') as f:
    lines = (re.sub(r'[^-+.0-9 ]+', '', line) for line in f)
    arr = np.genfromtxt(lines)

print(arr)

yields

[[-24.92 -23.66 -22.55]
 [-24.77 -23.56 -22.45]
 [-24.54 -23.64 -22.56]]

Thanks to Bitwise for clueing me in to this answer.