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

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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
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
% 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

Accepted Answer

Guillaume on 27 Jan 2015
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 = {};
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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More Answers (1)

Alessandro Masullo
Alessandro Masullo on 27 Jan 2015
Edited: Alessandro Masullo on 27 Jan 2015
The variable files is a cell array, and you are trying to refer it as a matrix. You should use files{i} instead of files(i,1) when you want to assign it:
for i=1:length(file_data);
files{i} = file_data(i).name;
Guillaume on 27 Jan 2015
y{i} = x
y(i) = {x}
are equivalent, when y does not exists or is already defined as a cell array.

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