Matlab read/use byte array without creating a file

Question

I have an array of bytes (which represents e.g. a CSV file) which are coming from C# in Matlab and I want to load this now without creating an temporary file.

Is there a possibility to do that? All methods I found are only taking filenames or requires that they will write it into a file.

Thanks!

Expect that on the server where it will run we don't have any rights to create files.. — Hannes H.
– Hannes H., Commented Mar 27, 2018 at 10:02
You have an array of bytes, but where? Internal memory? Is it a variable already in matlab? If it is in matlab, you could use textscan to convert a csv-like character vector to individual values. — Gelliant
– Gelliant, Commented Mar 27, 2018 at 11:14

Gelliant · Accepted Answer · 2018-03-28 10:13:59Z

3

Here I made a small csv file consisting of 8 values. Read it as uint8 it in matlab and used textscan to retrieve the original 8 values.

orgdat =    [132   231   334   234;   132   432   423   334];
csvwrite('temp.csv',orgdat);
fid = fopen('temp.csv');
dat = fread(fid,inf,'*uint8');fclose(fid);
cell2mat(textscan(char(dat),'%f,%f,%f,%f'))
>>
ans =
   132   231   334   234
   132   432   423   334

Or if you just want to scan for numbers:

result = cell2mat(textscan(char(dat),'%f','Delimiter',','))
>>
result =

   132   231   334   234   132   432   423   334

To reshape it you could look for the number of rows and reshape

rows = sum(dat==10)+(dat(end)~=10);
reshape(result,[],rows)'

edited Mar 28, 2018 at 10:13

answered Mar 27, 2018 at 11:35

Gelliant

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6 Comments

Hannes H. Over a year ago

That's exactly what I don't want. This is creating a file! And I don't have the data in clear text, I have them in bytes[]

Gelliant Over a year ago

That's why it is an example. I create a variable called dat that has bytes[] in it (32 bytes to be exact). Then in one line I convert it back to the original values. So I read a csv that is encoded as bytes[] variable. I thought that is what you wanted, if not, please make your question clear with an example. stackoverflow.com/help/how-to-ask

Hannes H. Over a year ago

sorry I went a little bit to fast over your example, brain didn't worked that well after lunch :D I just have tow more question, 1. you are using '%f%f%f%f' because we have 4 columns in one row, correct? What do I do if I don't know about the columns size? 2. What if it contains characters e.g. 1.64E-07?

Gelliant Over a year ago

correct. Basically you are sorting on commas (byte value 44) and returns (byte value 10). What you could do is split the byte[] based on value 10, and then count how many 44's you have. That +1 is the nr of columns. Scientific notation is no problem for textscan. Try cell2mat(textscan('1.64E-07','%f')). It will return the right number.

Gelliant Over a year ago

Yeah. Updated the answer. It had 1-3-5-7 ; 2-4-6-8 as the order. So it took column first. You want row first, since that's how you read it in.

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