Matrix from Python to MATLAB

Question

I'm working with Python and MATLAB right now and I have a 2D array in Python that I need to write to a file and then be able to read it into MATLAB as a matrix. Any ideas on how to do this?

Thanks!

Answer 1

If you use numpy/scipy, you can use the scipy.io.savemat function:

import numpy, scipy.io

arr = numpy.arange(9) # 1d array of 9 numbers
arr = arr.reshape((3, 3))  # 2d array of 3x3

scipy.io.savemat('c:/tmp/arrdata.mat', mdict={'arr': arr})

Now, you can load this data into MATLAB using File -> Load Data. Select the file and the arr variable (a 3x3 matrix) will be available in your environment.

Note: I did this on scipy 0.7.0. (scipy 0.6 has savemat in the scipy.io.mio module.) See the latest documentation for more detail

EDIT: updated link thanks to @gnovice.

Answer 2

I think ars has the most straight-forward answer for saving the data to a .mat file from Python (using savemat). To add just a little to their answer, you can also load the .mat file into MATLAB programmatically using the LOAD function instead of doing it by hand using the MATLAB command window menu...

You can use either the command syntax form of LOAD:

load c:/tmp/arrdata.mat

or the function syntax form (if you have the file path stored in a string):

filePath = 'c:/tmp/arrdata.mat';
data = load(filePath);

Answer 3

I wrote a small function to do this same thing, without need for numpy. It takes a list of lists and returns a string with a MATLAB-formatted matrix.

def arrayOfArrayToMatlabString(array):
    return '[' + "\n ".join(" ".join("%6g" % val for val in line) for line in array) + ']'

Write "myMatrix = " + arrayOfArrayToMatlabString(array) to a .m file, open it in matlab, and execute it.

Answer 4

I would probably use numpy.savetxt('yourfile.mat',yourarray) in Python and then yourarray = load('yourfile.mat') in MATLAB.

Answer 5

You could write the matrix in Python to a CSV file and read it in MATLAB using csvread.

Answer 6

You can also call matlab directly from python:

from mlabwrap import mlab
import numpy 
a = numpy.array([1,2,3])
mlab.plot(a)

Answer 7

The toolbox npy-matlab can read *.npy binary files into MATLAB. *.npy files can be directly exported with the NumPy module. From the documentation:

>> a = rand(5,4,3);
>> writeNPY(a, 'a.npy');
>> b = readNPY('a.npy');
>> sum(a(:)==b(:))
ans =

    60

npy-matlab is a simple collection of M-files available from GitHub, with a 2-clause BSD licence.