Working with the MIT arrhythmia database annotations: how can I convert the characters into numbers?

I work with MIT arrhythmia database and I want to group the annotations given for each beat in 5 classes, such as:

N={'N','L','R','e','j'}; %non_ectopic_beat
S={'A','a','J','S'};     %supra_ventricular_ectopic_beat
V={'V','E'};             %ventricular_ectopic_beats
F={'F'};                 %Fusion_beat
non_beats={'+','/','f','Q'};

How can I search into the annotation files of each ECG signal and replace the letter from those 5 groups with numbers from 1 to 5?

For example, when I have any of the non-ectopic beats ('N', 'L','R','e', or 'j' ) I want to have the label 1. For the secong class ('A','a','J','S') I want to have label 2 and so on.

I am also opened to other suggestion, as my goal is to append these annotatios to the feature set that I extracted from these signals.

The annotations files are in 'atr' format and I read them using the WFDB toolbox:

[ann,anntype]=rdann('100','atr'); 
%ann has the location of the R peak and anntype has the annotation of each heartbeat
anntype =

  2274×1 char array

    '+'
    'N'
    'N'
    'N'
    'N'
    'N'
    'N'
    'N'
    'A'
    'N'
    'N'
    'N'
 ...

[dpb]

For those totally unfamiliar with the subject matter, please attach a small section of the annotation file or the form of it that you have already read. The latter could be a .mat file, the former in whatever form they are, but the latter would be simpler for us to have the data already in memory instead of having to also write the code read a file in.

[Ioana Cretu]

I cannot attach them as they are too big, but they are available here: https://www.physionet.org/content/mitdb/1.0.0/

[dpb]

You can certainly make a small piece and attach it..."help us help you!"

[Ioana Cretu]

I attached a txt file with the annotations from one patient, hope it helps

Answer 1

[Shadaab Siddiqie]

From my understanding you want to replace few strings to few particular numbers. Here is the code which might help you.

content = fileread( 'ann.txt' ) ;
content = strrep( content, 'N', '1' ) ;
content = strrep( content, 'L', '1' ) ;
content = strrep( content, 'V', '3' ) ;
content = strrep( content, '+', '5' ) ;
fId = fopen( 'MyData_updated.txt', 'w' ) ;
fwrite( fId, content ) ;
fclose( fId ) ;

Then you can read new file as numbers.