Replacing edited Data with New Data to Save to Text File in Appdesigner

I upload a textfile with data and want to repalce the old data with new data, but I end up having both the old data and my new data.

How do I only save the new data?

function InputDataButtonPushed(app, event)
            [filename, path] = uigetfile('*.txt');
            figure(app.UIFigure);
            app.T = readtable(filename, 'Delimiter', 'space');
            
            app.ct = app.T(1,1);
            app.cr = app.T(1,2);
            
            app.ctEditField.Value = table2array(app.ct(1,1));
            app.crEditField.Value = table2array(app.cr(1,1));

                    function EditButtonPushed(app, event)
            app.T.ct(1) = app.ctEditField.Value;
            app.T.cr(1) = app.crEditField.Value;

             function SaveButtonPushed(app, event)
             
             Q = table2array(app.T(:,:));
fileid = fopen('filepath.txt','w');
fprintf(fileid, '%6.5f ', (Q));
fclose('all');

My output file shows the row of data for my old data and my new data like this:

0.09000 0.45000 2.00000 2.00000

Where the 2's are my new data.

Answer 1

[Voss]

My guess is that "ct" and "cr" are not the names of the columns/variables that readtable returns after reading the text file:

% make a file with column/variable names "a" and "b"
[fid,msg] = fopen('test_table.txt','w');
fprintf(fid,'a b\n0.09 0.45\n');
fclose(fid);

% read the file into a table T
T = readtable('test_table.txt','Delimiter','space')

T = 1×2 table
     a       b  
    ____    ____

    0.09    0.45

% setting ct and cr in the table adds new columns/variables
T.ct(1) = 2;
T.cr(1) = 2;
T

T = 1×4 table
     a       b      ct    cr
    ____    ____    __    __

    0.09    0.45    2     2 

If the text file did contain variable names "ct" and "cr", the new values from the EditFields would replace the values in the table:

% now make a file where the columns/variables are "ct" and "cr":
[fid,msg] = fopen('test_table.txt','w');
fprintf(fid,'ct cr\n0.09 0.45\n');
fclose(fid);

% read the file into a table T
T = readtable('test_table.txt','Delimiter','space')

T = 1×2 table
     ct      cr 
    ____    ____

    0.09    0.45

% this time, setting ct and cr replaces what's in the table
T.ct(1) = 2;
T.cr(1) = 2;
T

T = 1×2 table
    ct    cr
    __    __

    2     2 

If this is in fact the cause of the problem, you can fix it by ignoring the column/variable names when you read the file and then naming them "ct" and "cr" afterward:

% make a file with column/variable names "a" and "b" again
[fid,msg] = fopen('test_table.txt','w');
fprintf(fid,'a b\n0.09 0.45\n');
fclose(fid);

% read the file into a table T, this time telling readtable to ignore the
% column/variable names in the file (which will use names "Var1" and "Var2")
T = readtable('test_table.txt','ReadVariableNames',false)

T = 1×2 table
    Var1    Var2
    ____    ____

    0.09    0.45

% then rename "Var1" and "Var2" to "ct" and "cr"
T.Properties.VariableNames{'Var1'} = 'ct';
T.Properties.VariableNames{'Var2'} = 'cr';

% now setting ct and cr replaces what's in the table
T.ct(1) = 2;
T.cr(1) = 2;
T

T = 1×2 table
    ct    cr
    __    __

    2     2 

Of course, without having a sample text file where this problem happens, I can't say for sure what's going on. If you can't get it to work, upload a sample file we can use to test with.

Also, hard-coding the column/variable names suggests that readtable may not be the best way to read your files. Maybe readmatrix would be easier to work with.

[Voss]

("Answer" from @I moved to a comment:)

The files only have the data and I am excluding the variable names from the files. The input file appears as this:

0.09000 0.45000

Just the numbers in a row with one space in between each number.

I am only assigning a variable name to the numbers within the GUI.

I tried using readmatrix and I get more errors than I know how to deal with

app.T = readmatrix(filename, 'Delimiter', 'space');

Error using readmatrix (line 157)

"filename" must be a string scalar or character vector.

Error in Alpha/InputDataButtonPushed (line 125)

app.T = readmatrix(filename, 'Delimiter', 'space');

Error using matlab.ui.control.internal.controller.ComponentController/executeUserCallback (line 386)

Error while evaluating Button PrivateButtonPushedFcn.

[Voss]

If there are no variable names in the file, then MATLAB will use variable names Var1 and Var2 in the table it returns from readtable.

Because your code is setting the variables ct and cr in the table, here:

T.ct(1) = 2; % these values (2) come from your EditFields of course
T.cr(1) = 2;

that means you must first rename Var1 and Var2 to ct and cr:

T.Properties.VariableNames{'Var1'} = 'ct';
T.Properties.VariableNames{'Var2'} = 'cr';

because if you don't do that then your table will have all 4 variables Var1, Var2, ct, and cr in it, and you'll get an output file with four numbers instead of two, which was your observation.

The error with readmatrix is telling you that the file name you gave it is not the right data type to be a file name, e.g., maybe it's a number, when the file name should be a string (e.g., "test_table.txt") or a character vector (e.g., 'test_table.txt'). In the same situation but using readtable, you would've received the same error message, so this is not specific to readmatrix. This error can happen if you don't handle the case that the user clicked Cancel on the uigetfile dialog (because in that case filename is numeric 0), but you can do that like this:

[filename, path] = uigetfile('*.txt');
if isequal(filename,0)
    % return early (don't try to read 
    % the file) if no file was selected
    return
end
figure(app.UIFigure);
% read the file whichever way:
app.T = readmatrix(filename);
app.T = readtable(filename, 'Delimiter', 'space');

[Voss]

("Answer" from @I moved to a comment:)

I tried adding and replacing the code:

[filename, path] = uigetfile('*.txt');
            
            if isequal(filename,0);
                return
            end    

I get the error with readmatrix here

            app.ctEditField.Value = app.T(1);

Error using matlab.ui.control.internal.model.AbstractNumericComponent/set.Value (line 185)

'Value' must be a double scalar within the range of 'Limits'.

It's referring to the value changed function

function ctEditFieldValueChanged(app, event)
            value = app.ctEditField.Value;
            
       end

            app.T.Properties.VariableNames{'Var1'} = 'ct';

Unable to perform assignment because dot indexing is not supported for variables of this type.

            T.Properties.VariableNames{'Var1'} = 'ct';

Expected one output from a curly brace or dot indexing expression, but there were 4 results.

I am a bit confused. Do you mean that I must use readmatrix? I cannot get the numbers to load when using readmatrix, but I can with readtable.

I tried changing the variable names. I have no idea how to troubleshoot an error like this.

[Voss]

If you use readmatrix then app.T is not a table, it's a matrix, so the syntax for working with it is completely different. The errors you see are not from readmatrix itself, but are because you are treating app.T as if it were a table when it is not.

function InputDataButtonPushed(app, event)
    
    [filename, path] = uigetfile('*.txt');
    if isequal(filename,0)
        return
    end
    
    figure(app.UIFigure);
    app.T = readmatrix(filename);
    
    % the error "'Value' must be a double scalar within the range of
    % 'Limits'." can be avoided by making sure the Value is within the
    % Limits:
    lim = app.ctEditField.Limits;
    app.ctEditField.Value = min(lim(2),max(lim(1),app.T(1,1)));
    lim = app.crEditField.Limits;
    app.crEditField.Value = min(lim(2),max(lim(1),app.T(1,2)));


function EditButtonPushed(app, event)
    app.T = [app.ctEditField.Value app.crEditField.Value];
    
    
function SaveButtonPushed(app, event)
    Q = app.T;
    fileid = fopen('filepath.txt','w');
    fprintf(fileid, '%6.5f ', Q);
    fclose('all');

[I]

I still cannot open the file using READMATRIX. I have an error on this line

app.ctEditField.Value = min(lim(2), max(lim(1), app.T(1,1)));

Row index exceeds table dimensions.

The input file looks exactly like this: 0.09 0.45

I am really not sure why I am unable to open the file.

[Voss]

I can't help you if you only share the line where the error is. Without any context, I can't say anything about that line.

The problem is not readmatrix, since (presumably) the line where readmatrix is used executes without error. The problem is something in between using readmatrix and the line with the error. Without knowing what happens in between, I can't say how to fix it.

[Voss]

(Answer moved here:)

function InputDataButtonPushed(app, event)
            [filename, path] = uigetfile('*.txt');
            
            if isequal(filename,0);
                return
            end
            
            figure(app.UIFigure);
%             app.T = readtable(filename); %, 'Delimiter', 'space');
            app.T = readmatrix(filename); %, 'Delimiter', 'space');

              lim = app.ctEditField.Limits;
              app.ctEditField.Value = min(lim(2), max(lim(1), app.T(1,1)));
              lim = app.crEditField.Limits;
              app.crEditField.Value = min(lim(2), max(lim(1), app.T(1,2)));
              

Perhaps I have a syntax error somewhere?

[Voss]

And you get the error, "Row index exceeds table dimensions." on this line:

app.ctEditField.Value = min(lim(2), max(lim(1), app.T(1,1)));

Is that correct?

You can place a breakpoint on that line and inspect what the value of app.T is.

I don't see any syntax errors.

[I]

It says NaN and I really do not understand why. I don't see any syntax errors either.

Is there an issue with using readtable? Or do you believe that I must use readmatrix?

[I]

I am just going back to using readtable and I will stick to the default variable names within the code since that essentially fixes the entire problem at the moment. At the moment, I am just trying one input file. I am not sure how the default variable names will change when I use more than one input file within the same code. At least it works for now with the one input file.