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

Question

I 2022-4-9

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1692440-replacing-edited-data-with-new-data-to-save-to-text-file-in-appdesigner

评论： I 2022-4-20

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.

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Answer 1

Voss 2022-4-9

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1692440-replacing-edited-data-with-new-data-to-save-to-text-file-in-appdesigner#answer_938840

在 MATLAB Online 中打开

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.

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Voss 2022-4-10

在 MATLAB Online 中打开

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 2022-4-11

在 MATLAB Online 中打开

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 2022-4-18

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 2022-4-20

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.

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