Why does readmatrix return empty matrix if text file contains quotes?

Function readmatrix fails to read data from text file when it contains quotes. Why? How to make readmatrix working?

Extended example:

let first text.txt be:

header1
header2
1
2
3
footer

then

readmatrix('text.txt', 'Range', [3 1 5 1])

gives usual vector [1;2;3].

But whe text.txt is like this:

"
header2
1
2
3
"

readmatrix returns empty vector while dlmread works fine.

How to force readmatrix ignore quotes?

[the cyclist]

It would be better to upload the two different text files (using the paperclip icon in the INSERT section of the toolbar), rather than relying on users to transcribe them to reproduce your files.

[Stephen23]

"Function readmatrix fails to read data from text file when it contains quotes. Why?"

Because double quotes indicate that everything until the next double quote are considered to be one text string. So your sample file consists of exactly one field with some text in it. This is a basic feature of delimited text files (e.g. CSV).

[Konstantin]

Thank you for the comments. I also understood that readmatrix seems to treat file with quotes like a single long string. But how to make it ignore the quotes?

readmatrix(filename, 'Range', [range without quotes'] does not work unfortunately.

I have something like hundreds of files with quotes. I of course can preprocess them to remove those, but would be nice to use readmatrx straight away.

I've uploaded test files.

Answer 1

[Cris LaPierre]

readmatrix is trying to guess what the file format is. However it is doing that, it appears to not handle this specific configuation as you might expect. My suspicion is that it is treating everything between the 2 quotes as strings, and readmatrix ignores strings.

You might want to consider reporting this here:

https://www.mathworks.com/support/contact_us.html

[Cris LaPierre]

Following up, I do not know of a way around this with readmatrix. However, this code seems to be able to import the file with quotes correctly using readtable.

T = readtable('test_quotes.txt','Format','%f','numHeaderLines',2,'readVariableNames',false,'Whitespace','"');
T2 = table2array(T)

T2 = 6x1

1 2 3 4 5 6

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