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How to extract formatted hex data from a text file?

Asked by Stanislav Steinberg on 4 Jul 2018
Latest activity Commented on by Stanislav Steinberg on 5 Jul 2018
I have a text file with tens of thousands of lines formatted like so:
...
[11:52:30.739] : Value: [BC-7F-00-00-F7-F6-2A-D7-24-D9-81-EE-6A-DD-08-D4-BD-D5-09-E1-10-F5-22-DB-20-DE-55-EA-21-D9-22-D1-EA-D5-45-E5-95-F8-2A-D7-22-DA-12-EF-95-DD-2A-D3-85-D4-5A-E1-EB-F6-2A-DB-22-DE-54-EA-A2-D8-7D-CF-15-D4-0A-E5-FB-FA-88-D6-A5-D9-D1-EA-80-DC-95-D1-24-D2-2D-E1-D5-F9-AA-DA-DA-DD-AA-E6-BD-D7-56-CE-D5-D1-5A-E5-5B-FD-D5-D5-55-DA-A8-E9-DA-DB-EF-CF-11-D0-D5-E1-15-FC-EA-D9-21-DE-D5-E6-A0-D6-B5-CD-0A-D0-EE-E6-55-FF-20-D5-55-DB-DE-E9-D5-DA-96-CE-2A-CE-5A-E3-DD-FC-EA-D8-F6-DD-55-E7-D5-D5-8A-CE-16-D0-A8-E8-15-FE-D4-D5-6A-DC-D5-EA-AA-DA-2A-CF-22-CE-A5-E4-B5-FC-6A-D9-4A-DE-AA-E8-FA-D5-A2-CF-12-D1-AA-E9-A0-FD-4A-D6-55-DC-EA-EB-95-DA-F5-CF-2A-CF-94-E4-EA-FB-CA-D9-40-DE-D5-E8-5A-D6-44-D0-2A-D2-B5-E9-2A-FD-40-D6-AA-DC-DB-EB-AB-DA-E8-CF-55-CF-6A-E4]
[11:52:30.777] : Value: [CB-7F-00-00-FF-FB-2A-D5-2A-DA-2D-EC-95-DB-B6-D0-2A-D1-B5-E5-DA-FA-15-D9-2A-DF-B6-E8-7F-D7-02-CD-55-D1-45-E9-4A-FE-AA-D4-D5-DA-D5-EB-EA-DB-0A-CF-20-D0-AA-E5-AF-FC-69-D9-DA-DE-AA-E6-55-D7-2A-CC-55-D0-56-E9-95-FF-00-D5-81-DA-55-E8-95-DB-95-CE-22-CF-56-E6-F6-FD-D5-D8-A4-DE-55-E5-5B-D6-B5-CC-D2-CF-16-EB-2A-01-85-D4-29-DB-AA-EA-AA-DA-BF-CE-D5-CE-44-E7-2A-FC-90-D9-4A-DD-2A-E5-A8-D6-AA-CD-55-D1-AD-E9-AA-FE-35-D4-EA-D8-24-E8-CA-DA-6D-D0-6A-D0-B5-E5-DD-FC-B6-D8-6A-DD-56-E5-85-D6-D2-CD-A5-D0-AB-E9-11-00-82-D4-15-DA-55-EA-0A-DB-15-D0-55-CF-6A-E6-50-FA-EA-D9-40-DC-AA-E5-28-D7-AA-CD-6E-D1-A4-E8-55-FB-7A-D5-55-D7-2A-E8-B6-DA-95-D1-7A-D1-5D-E5-57-F8-7D-D9-20-DD-0A-E7-DE-D7-20-CE-1A-D2-D5-E7-94-FC-5A-D5-89-D8-4A-EA-94-DB-AB-D1-D6-D1-AA-E4]
...
I need to extract the hex data in the following way: The first 32 bits are an index, and the following words are actual data.
Currently I'm parsing the file line-by-line and extracting the hex data using regexp. This is slow. In the end I'm getting a matrix with doubles that I can manipulate quickly.
There must be a faster method to extract this data and I don't know it. Perhaps you can help?

  2 Comments

What's the data encoding scheme?
What does your regexp look like? Perhaps it could be improved for efficiency.

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R2018a

1 Answer

Answer by Guillaume
on 4 Jul 2018
Edited by Guillaume
on 4 Jul 2018
 Accepted Answer

How about:
filecontent = fileread(yourfile); %read everything at once
hexstrings = regexp(filecontent, '(?<=Value: \[)[^\]]*(?=\])', 'match');
decvalues = cell2mat(cellfun(@(hex) sscanf(hex, '%x-'), hexstrings, 'UniformOutput', false))';
This may be faster:
filecontent = fileread(yourfile); %read everything at once
hexstrings = regexp(filecontent, '(?<=Value: \[)[^\]]*(?=\])', 'match');
decvalues = reshape(sscanf(strjoin(hexstrings, '-'), '%x-'), [], numel(hexstrings))';
Unfortunately, textscan doesn't have a '%x' format specifier.

  2 Comments

A major foobar, too... :( I added the enhancement request not long after it was introduced; like many simple but apparently not sexy-enough things, it's never made the cut of what gets attention.
Guillaume, brilliant! So far it looks much faster than what I previously coded. Good to learn. Thanks.

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