Clear Filters
Clear Filters

Convert numpy ndarray to matlab mlarray in python

20 views (last 30 days)
mlarray to ndarray: np.asarray(x._data, dtype=dtype)
but inversely, ndarray to mlarray: matlab.double(x.tolist()), which is extremely slow, is there a more efficient way to do this? Thank u for answering.

Accepted Answer

Al Danial
Al Danial on 28 Apr 2022
Looks like you're making the data load unnecessarily complicated. The file actually loads cleanly into a NumPy array:
from import loadmat
data = loadmat('data.mat', squeeze_me=True)
x = data['data']
array([[0.00000000e+00, 5.90000000e+01, 5.90000000e+01, 2.25296241e+05],
[1.00000000e+00, 6.20000000e+01, 5.81599120e+01, 5.93159561e+04],
[2.00000000e+00, 1.00000000e+02, 9.47518190e+01, 3.22666379e+04],
[2.04500000e+03, 4.00000000e+00, 4.88991300e+00, 3.01840538e+04],
[2.04600000e+03, 2.00000000e+00, 2.26899200e+00, 6.46032757e+04],
[2.04700000e+03, 1.00000000e+00, 1.00000000e+00, 1.18671912e+05]])
Simplify your function load_mat to
def load_mat(pth_mat, key=None):
data = loadmat(pth_mat, squeeze_me=True)
print(data.keys()) if key is None else None
return data[key]
then call it like this
x1 = load_mat('data.mat', 'data')

More Answers (3)

Al Danial
Al Danial on 21 Apr 2022
Which version of MATLAB? 2020a and newer (I don't have easy access to older versions) should just be able to do
>> mx = double(x);
without a conversion to a list.
Gan Lee
Gan Lee on 24 Apr 2022
Thanks. Its 2021b , I tried this but not available.
Christopher Wunder
Christopher Wunder on 23 Aug 2022
This is not possible for me either.
The function _is_initializer in checks for the input to be of type and a numpy.ndarray fails to be of such a type. The only way (without altering the package) is to convert the array beforehand or pass any kind of Sequence to it instead of an array.

Sign in to comment.

Al Danial
Al Danial on 24 Apr 2022
Now I'm curious what is in your variable x. Can you make a small version of this data, write it to a .mat file, then attach the .mat file?

Gan Lee
Gan Lee on 27 Apr 2022
Edited: Gan Lee on 27 Apr 2022
Here is part of my python code:
# -*- coding: utf-8 -*-
import numpy as np
from import loadmat
import h5py
import matlab
from matlab import engine
from matlab import mlarray
def load_mat(pth_mat, key=None):
data = loadmat(pth_mat)
print(data.keys()) if key is None else None
return data.get(key)[:].astype(np.double)
def mlarray2ndarray(x: mlarray):
return np.asarray(x._data, dtype=np.double)
def ndarray2mlarray(x: np.ndarray):
return matlab.double(x)
if __name__ == "__main__":
eng = engine.start_matlab()
pth_mat = r".\data.mat"
# np to matlab
x1: np.ndarray = load_mat(pth_mat, key="data")
# mx1: mlarray = ndarray2mlarray(x1) #WRONG
mx1 = matlab.double(x.tolist()) #OK, BUT VERY SLOWLY
# matlab to np
mx2: mlarray = eng.load(pth_mat).get("data")
x2: np.ndarray = mlarray2ndarray(mx2) #OK
# ......
here is errcode:
initializer must be a rectangular nested sequence


Find more on Platform and License in Help Center and File Exchange




Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!