writematrix output file that can't be read by textread

I am using writematrix to write a 2D matrix to csv, and read this csv later elsewhere (e.g., Python Numpy).

The problem is that this file always errors, even when I read this file using textread.

Would you please help me?

Here is a sample code to reproduce the issue:

filename_ = 'sample_matrix.csv';
writematrix(rand(20,30), filename_);
textread(filename_) % this errors

Answer 1

[Walter Roberson]

The format specification is mandatory for textread

Perhaps you wanted readmatrix or readlines or fileread

[Mahmoud Elzouka]

In Matlab, it shows me this error:

Error using dataread

Trouble reading number from file (row 2, field 1) ==>

In Python using numpy.loadtxt, it shows me this error:

ValueError: could not convert string '1.703,1.703,1.703,1.991,1.991,1.991,1.991,1.991,1.991,1.991,1.991,1.991,1.991,1.991,1.991,1.991, to float64 at row 0, column 1.

It looks like Matlab is adding some special charachter at the beginning of the file that make it not easy to read by other readers

Do you know how to get rid of this special charchter?

[Walter Roberson]

 happens to be the UTF-8 Byte Order Mark https://en.wikipedia.org/wiki/Byte_order_mark

It is not generally recommended to use Byte Order Mark for UTF-8 files, but software "should" ignore it when present (or specifically treat it as indicating UTF-8 encoding.)

The Byte Order Mark is not added to the file on my (MacOS) system, but possibly you are using Windows with a default character set that is different than UTF-8... in such a case maybe MATLAB adds the mark automatically.

For cases in which you are not writing out strings with extended characters, you could try something like

writematrix(rand(20,30), filename_, 'windows1251');

and see if that helped.

[Mahmoud Elzouka]

When I changed the encoding to 'windows1251', the file can be read by numpy.loadtxt. Thanks for your help.

FYI, this still errors:

filename_ = 'windows1251.csv';
writematrix(rand(20,30), filename_, 'Encoding', 'windows1251');
textread(filename_) % this errors

[Walter Roberson]

textread must be given at least two parameters. textread is for reading formatted data and you have to tell it the format. textread is not for reading a file as a single character vector: I already gave links to two routines for that.