Try catch to load files

Hi!! I'm writing a program in which I have to load multiple files within a cycle and work with them.

The program calls the different files each time it runs the cycle but I would luke to know what is the best way to handle an error when the file it is trying to load doesn't exist so it just continues to the next one, eliminating the need to stop the program run.

I thought of doing this with a try catch but couldn't find exactly how in the documentation

Answer 1

[Walter Roberson]

cminfo = which('cameraman.tif');
cmdir = fileparts(cminfo)

cmdir = '/MATLAB/toolbox/images/imdata'

dinfo = dir(cmdir);
dinfo([dinfo.isdir]) = [];
filenames = fullfile({dinfo.folder}, {dinfo.name});
nfiles = length(filenames);

results = cell(nfiles, 1);

for K = 1 : nfiles
    thisfile = filenames{K};
    try
      %demonstration processing
      fileinfo = imfinfo(thisfile);
      results{K} = fileinfo;
    catch ME
       fprintf('not image file: "%s"\n', thisfile);
       continue
    end
end

not image file: "/MATLAB/toolbox/images/imdata/CT-MONO2-16-ankle.dcm"
not image file: "/MATLAB/toolbox/images/imdata/Contents.m"
not image file: "/MATLAB/toolbox/images/imdata/DICOMDIR"
not image file: "/MATLAB/toolbox/images/imdata/US-PAL-8-10x-echo.dcm"
not image file: "/MATLAB/toolbox/images/imdata/brain.nii"
not image file: "/MATLAB/toolbox/images/imdata/brainMRI.hdr"
not image file: "/MATLAB/toolbox/images/imdata/brainMRI.img"
not image file: "/MATLAB/toolbox/images/imdata/buildingPixelLabeled.mat"
not image file: "/MATLAB/toolbox/images/imdata/cellsequence.mat"
not image file: "/MATLAB/toolbox/images/imdata/contours.mat"
not image file: "/MATLAB/toolbox/images/imdata/defaultBRISQUEModel.mat"
not image file: "/MATLAB/toolbox/images/imdata/defaultDnCNN-B-Grayscale.mat"
not image file: "/MATLAB/toolbox/images/imdata/defaultNIQEModel.mat"
not image file: "/MATLAB/toolbox/images/imdata/eSFRdefaultColorReference.mat"
not image file: "/MATLAB/toolbox/images/imdata/eSFRdefaultGrayReference.mat"
not image file: "/MATLAB/toolbox/images/imdata/imdemos.mat"
not image file: "/MATLAB/toolbox/images/imdata/knee1.dcm"
not image file: "/MATLAB/toolbox/images/imdata/knee2.dcm"
not image file: "/MATLAB/toolbox/images/imdata/lab8.icm"
not image file: "/MATLAB/toolbox/images/imdata/littlecoriver.lan"
not image file: "/MATLAB/toolbox/images/imdata/mississippi.lan"
not image file: "/MATLAB/toolbox/images/imdata/monitor.icm"
not image file: "/MATLAB/toolbox/images/imdata/montana.lan"
not image file: "/MATLAB/toolbox/images/imdata/mristack.mat"
not image file: "/MATLAB/toolbox/images/imdata/niftiHeaderExample.hdr.gz"
not image file: "/MATLAB/toolbox/images/imdata/office.hdr"
not image file: "/MATLAB/toolbox/images/imdata/paris.lan"
not image file: "/MATLAB/toolbox/images/imdata/pendulum.mat"
not image file: "/MATLAB/toolbox/images/imdata/peppers.dpx"
not image file: "/MATLAB/toolbox/images/imdata/regioncoordinates.mat"
not image file: "/MATLAB/toolbox/images/imdata/rhinos.avi"
not image file: "/MATLAB/toolbox/images/imdata/rio.lan"
not image file: "/MATLAB/toolbox/images/imdata/rirePatient007CT.bin"
not image file: "/MATLAB/toolbox/images/imdata/rirePatient007CT.header"
not image file: "/MATLAB/toolbox/images/imdata/rirePatient007MRT1.bin"
not image file: "/MATLAB/toolbox/images/imdata/rirePatient007MRT1.header"
not image file: "/MATLAB/toolbox/images/imdata/rtstruct.dcm"
not image file: "/MATLAB/toolbox/images/imdata/spiralVol.mat"
not image file: "/MATLAB/toolbox/images/imdata/tokyo.lan"
not image file: "/MATLAB/toolbox/images/imdata/traffic.avi"
not image file: "/MATLAB/toolbox/images/imdata/traffic.mj2"
not image file: "/MATLAB/toolbox/images/imdata/trees.mat"
not image file: "/MATLAB/toolbox/images/imdata/westconcordpoints.mat"

results

results = 153×1 cell array
    {1×1 struct}
    {1×1 struct}
    {1×1 struct}
    {1×1 struct}
    {1×1 struct}
    {1×1 struct}
    {1×1 struct}
    {1×1 struct}
    {1×1 struct}
    {1×1 struct}
    {0×0 double}
    {0×0 double}
    {0×0 double}
    {1×1 struct}
    {0×0 double}
    {1×1 struct}

[Ana Gabriela Guedes]

Thank you!

Answer 2

[Image Analyst]

The best way is to follow the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

You create a loop where you either only have files that exist (if you use the dir() function), or you check if the file exists with exist() or isfile(), and then you'll only process the files that do exist so no error ever gets thrown and there is no need to put

try
    % Try to open file with whatever function you want.
catch ME
    % Error opening the file, like it doesn't exist or you don't have permission.
    continue; % Skip to bottom of for loop but continue interating.
end

but again, the above code is not recommended and I recommend you do it like in the FAQ.

[Ana Gabriela Guedes]

Thank you!