Error Message "Array indices must be positive integers or logical values" from importing .txt file and get plot

I am trying to import a few .txt files and have them plot in the same figure, but I keep getting the following error and have no idea how to fix that.

Error Message:

Array indices must be positive integers or logical values.

Error in Ecoli_K12_20231229_PhosphateBuffer_6 (line 43)

plot(time, Ion,'fileNames', fileNames{fileidx-1});

clc;
clear all;
close all;

% Get list of files. 
filelist = dir('G:\Processed PTR Data\20231229_E. coli K12_Phosphate Buffer\Class II Ion\*.txt');

%Loop to read all files:

spectra = cell(size(filelist));  %stored in a file array at first

opts = detectImportOptions(fullfile(filelist(1).folder, filelist(1).name), 'ExpectedNumVariables', 2);

Index exceeds the number of array elements. Index must not exceed 0.

for fileidx = 1:numel(filelist)

    spectrum= readtable(fullfile(filelist(fileidx).folder, filelist(fileidx).name), opts);  %read file

    spectrum.Source = repmat({filelist(fileidx).name}, height(spectrum), 1);  %add a variable indicating the source. Maybe you want to use only part of the filename
    
    time = spectrum(:,1)./3600;
    
    spectra{fileidx} = spectrum;
    
    AllSpec(:, fileidx) = spectrum(:, 2);




    AllSpecTable = array2table(AllSpec);



    Ions = AllSpecTable(:, fileidx);

    Ion = table2array(Ions);


    fileNames{fileidx} = extractBetween(regexprep(filelist(fileidx).name, '20(\w+)=', 'mQ='), '','.txt');

    plot(time, Ion,'fileNames', fileNames{fileidx-1});

    hold on;

end

hold off

Answer 1

[Stephen23]

plot(time, Ion,'fileNames', fileNames{fileidx-1});
%                                            ^^ get rid of this

[Yingxi]

I removed the "-1" and got similar error messages.

Error using plot

Invalid subscript for Y. A table variable subscript must be a

numeric array containing real positive integers, a logical array,

a character vector, a string array, a cell array of character

vectors, or a pattern scalar used to match variable names.

Error in Ecoli_K12_20231229_PhosphateBuffer_6 (line 43)

plot(time, Ion,'fileNames', fileNames{fileidx});

[Stephen23]

"I removed the "-1" and got similar error messages."

No, you get a totally different error message from a totally different bug in your code.

Your code mixes up tables and numeric arrays, with several superfluous conversions between those data types. And that code around ALLSPEC and ALLSPECTABLE is convoluted. Does it work? Given that confusion, such an error is not unexpected.

The basic problem of the error message is that you are trying to plot tables, whereas you should be plotting numeric data:

X = [1;2;3;4];
Y = rand(4,1);
T = table(X,Y);
plot(T{:,1},T{:,2}) % what you should be doing

plot(T(:,1),T(:,2)) % what you are doing

Error using plot
Invalid subscript for Y. A table variable subscript must be a numeric array containing real positive integers, a logical array, a character vector, a string array, a cell array of character vectors, or a pattern scalar used to match variable names.

Look at your data in the variable viewer: the only table you should have is SPECTRUM, the rest should be numeric. Get rid of those TABLE2ARRAY and ARRAY2TABLE calls... simplify your code!

I would start again. Use curly braces to obtain the numeric arrays, not parentheses. Making a lot of assumptions about the sizes and data types, perhaps something like this:

S = dir('G:\Processed PTR Data\20231229_E. coli K12_Phosphate Buffer\Class II Ion\*.txt');
F = fullfile(S(1).folder,S(1).name);
I = detectImportOptions(F, 'ExpectedNumVariables', 2);

for k = 1:numel(S)
    
    F = fullfile(S(k).folder,S(k).name);
    T = readtable(F, I);
    T{:,'Source'} = {S(k).name};
    S(k).data = T;
    S(k).ions = T{:,2};
    
    time = T{:,1}./3600; % curly braces!
    Ion  = T{:,2};       % curly braces!
    
    N = regexprep(S(k).name, {'20(\w+)=','\.txt$'}, {'mQ=',''});
    
    plot(time, Ion, 'DisplayName',N); % correct option name
    hold on;
end
hold off

alltables = vertcat(S.data) % depends on the table column names, which you have not told us
allions   = horzcat(S.ions)

Of course this is untested code because you did not provide us with any test files.