How to skip every second file in directory for for loop

I have a folder of .wav files which I am cutting to a shorter length and then re-writing. I would like to do this for every second file in the directory.

How can I adapt my code to do this?

direcName = 'H:\SoundTrap\wav\New folder\*.wav'; %folder                                                
directory = dir(direcName); %all files in folder
[pathstr,name,ext] = fileparts(direcName);


for i=1:length(directory)
    usefile = directory(i).name;                                       
    fileName = strcat(pathstr,'\',usefile);                              
    [y, Fs] = audioread(fileName,[1 2]);                      
    
    startpos = 4 * Fs; %start position in seconds
    endpos = 119 * Fs; %end position in seconds

    % Store edited version
    [ynew, Fs] = audioread(fileName, [startpos endpos]); %read in section of file
        
    % Write new file
    [pathstr,name,ext] = fileparts(fileName);
    folder='H:\SoundTrap\wav\New folder\Cut files';
    outFileName = strcat(folder, '\', name, '.cut',ext);
    audiowrite(outFileName, ynew, Fs);
end

[Mrutyunjaya Hiremath]

@Louise Wilson ,

This is the good way to do it.

[Stephen23]

You can improve the code by using fullfile rather than concatenating strings, e.g. replace this:

fileName = strcat(pathstr,'\',usefile);

with

fileName = fullfile(pathstr,usefile);

[Louise Wilson]

Thanks Stephen! Updated to answer re:Image Analyst, all good!

Answer 1

[Louise Wilson]

The answer is...

direcName = 'H:\SoundTrap\wav\New folder\*.wav'; %folder                                                
directory = dir(direcName); %all files in folder
[pathstr,name,ext] = fileparts(direcName);
for i=1:2:length(directory)
    usefile = directory(i).name;                                       
    fileName = fullfile(pathstr, usefile);                              
    [y, Fs] = audioread(fileName,[1 2]);                      
    
    startpos = 4 * Fs; %start position in seconds
    endpos = 119 * Fs; %end position in seconds
    % Store edited version
    [ynew, Fs] = audioread(fileName, [startpos endpos]); %read in section of file
        
    % Write new file
    [pathstr,name,ext] = fileparts(fileName);
    folder='H:\SoundTrap\wav\New folder\Cut files';
    outFileName = strcat(folder, '\', name, '.cut',ext);
    audiowrite(outFileName, ynew, Fs);
end

[Stephen23]

• replace string concatenation with fullfile and sprintf.
• avoid the first fileparts by providing just the directory path.
• unused output arguments replaced with tilde ~

D = 'H:\SoundTrap\wav\New folder';
S = dir(fullfile(D,'*.wav'));
for k = 1:2:numel(S)
    F = fullfile(D,S(k).name);
    [~,Fs] = audioread(F,[1,2]);
    % read in section of file:
    [y,Fs] = audioread(F,Fs.*[4,119]);
    % Write new file
    [~,N,E] = fileparts(S(k).name);
    F = fullfile(D,'Cut files',sprintf('%s.cut%s',N,E));
    audiowrite(F,y,Fs);
end

[Benjamin Colbert]

To modify this to skip 23 files (e.g., read one file per day), would you simply change for i=1:2:length(directory) to for i=1:24:length(directory)

[Louise Wilson]

Yes, that will select every 24th item of i. Run the first couple of iterations and check it's selecting what you think it is/want it to. It will only work to select one file per day if you have 24 files per day.