MATLAB: HELP with Undefined variable, size of the indicated variable changes with each loop iteration.

undefined function

Hello, i have been running a code during some time and it worked. However now, i am trying to run it and it does not run because of this error message:
??? Undefined function or variable 'files'.
Error in ==> after_all at 20 coord = regexp(files,'\d+(\.\d+)?','match'); % It extracts the coordinates from the name of each file
The problem is the variable files (The size of the indicated variable or array appears to be changing with each loop iteration) it says…
Can anyone help me, please?
This is my code:
clear all;  % clear all variables
      close all;  % close all plot windows
      clc;        % clear the command window
        workfolder='C:\Users\Jorge\Desktop\Airfoil_BASELINE_Measurements\Airfoil_BASELINE_Measurements\Re140k00deg'; % It defines the folder (rpm or Re) to run
        folders=[                       % It indicates that in the folder selected we are interested in the Hot Wire measurements
            {'cdaq2mod2_ai0-hw\'}
            {'cdaq2mod2_ai1-hw\'}
            ];
        file_data=dir([workfolder folders{1} 'x*.dat']);    %Inside the hot wire measurements we look for all the files with an "x" in its name
        for i=1:length(file_data); 
            files(i,1)={file_data(i).name}; % It creates a variable with all the names of the files
        end
        % files=[
        %     {'x_+0.000mm_y_+0.000mm_z_+0.000mm.dat'}
        %     {'x_+0.000mm_y_+5.000mm_z_+0.000mm.dat'}
        %     ];
        coord = regexp(files,'\d+(\.\d+)?','match'); % It extracts the coordinates from the name of each file
        xyzCoords = cell2mat(cellfun(@(x)str2num(char(x))',coord,'UniformOutput',false)); % It organize the coordinates properly

Best Answer

The error is Undefined function or variable 'files'. files is defined inside your for loop. So if it is undefined after the loop that means your loop didn't execute. The only reason for your loop not to execute is that length(file_data) is 0, i.e. no file was found.
Morale of the story: when interacting with the filesystem (or any data outside your program control, like user input), always check that you're getting what you're expecting. In this case, do check that there is at least one file.
Note: You don't need a loop to transform the structure returned by dir into a cell array of filenames:
files = {file_data.name};
works just as well. It would also have avoided the undefined variable error in regexp (which would just have returned an empty cell array. Most likely, another error would occur later because you haven't designed your code to cope with no file being found.
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