Problem appending a variable to an existing text file using save

I have some measurements in a cell array.

data ={... 
    'AS-01_09'    [     52]       [451]    [4724]   [1]
    'AS-01_08'    [38.3000]       [451]    [4724]   [1]
    'AS-01_07'    [     37]       [451]    [4724]   [1]
    'AS-01_06'    [23.1000]       [451]    [4724]   [1]
    'AS-01_05'    [25.6000]       [451]    [4724]   [1]
    'AS-01_04'    [     89]       [451]    [4724]   [1]
    'AS-01_03'    [75.8000]       [451]    [4724]   [1]  
    'AS-01_02'    [49.6000]       [451]    [4724]   [1]  
    'AS-01_01'    [26.3000]       [451]    [4724]   [1]  
    'AS-02_5'     [38.2000]       [489]    [4736]   [2]  
    'AS-02_4'     [     45]       [489]    [4736]   [2]  
    'AS-02_3'     [44.7000]       [489]    [4736]   [2]  
    'AS-02_2'     [44.2000]       [489]    [4736]   [2]  
    'AS-02_1'     [47.3000]       [489]    [4736]   [2]};

Column 1 has station codes (names), column 2 measurement values, column 3 local X coordinates, column 4 local Y coordinates, column 5 location flag (there are multiple stations for each location).

I also have in a separate cell location names. Stations from the same location have the same location name.

loctns={... 
'AS-01'       
'AS-01'       
'AS-01'
'AS-01'       
'AS-01'       
'AS-01'
'AS-01'       
'AS-01'       
'AS-01'
'AS-02'       
'AS-02'       
'AS-02'       
'AS-02'       
'AS-02'};

I am trying to separate the measurements by location and save each location to a separate file. I also want to smooth the measurements and do the same for the smoothed measurements.

This is my code:

   %%Get measurements' matrix
    measurements=cell2mat(data(:,2:5));

    %%Split 'measurements' matrix based on  flag in first column
    A = arrayfun(@(x) measurements(measurements(:,4) == x, :),...
        unique(measurements(:,4)),'uniformoutput', false);

    %%Get the list of unique location names
    loctn_names=unique(loctns);

    %%Smooth measurements
    % Save smoothed and original values to a separate file for each location

    [rw,cw]=size(loctn_names);
    count=0;
    for i = 1:rw
    values = A{i,:}(:,1); % access arrays in 'A' with content indexing (curly 
                          % brackets) then access first column (values) with 
                          % regular indexing (parentheses)

    j=length(values);                 % access variable 'data' to create 
    stations=data(count+1:count+j,1); % a 1D array of station names
    count=count+j;                    % to append to the output file

    IN = A{i,1}(:,1:3);               % creating matrix of data for each loctn
    tempname=strcat(char(loctn_names(i)),'_X-Y-V.txt');  % temporary file name                                                   

    save(tempname, 'IN', '-ASCII');        % save matrix of data to output file 
    %save(tempname, 'stations', '-append'); % append station names to file

    valuesSM=conv(values,[0.5 1 0.5],'same')/2;  % smoothing  by convolution 
    valuesSM(1)=values(1); 
    valuesSM(end)=values(end);                   % ensuring extremes are same
                                                 % as in original values
    OUT = IN; OUT(:,1)=valuesSM(:);    % creating matrix of data for each loctn
    tempname1=strcat(char(loctn_names(i)),'_X-Y-smooth_V.txt')      % file name

    save(tempname1, 'OUT', '-ASCII');      % save matrix of data to output file
    %save(tempname1, 'stations', '-append');    % append stations names to file

    end

It is all working as expected, except for the two lines to append the station names, which are commented out. If I uncomment them, I get this error message:

Error using save
Unable to write to MAT-file \\...\Measurements\AS-01_X-Y-V.txt
File may be corrupt.

Does the append option as described in here only apply to .mat files? If yes, in what other way can I append the variable to the output file?

Thank you.

Answer 1

[James Tursa]

You still need to tell MATLAB that it is an ASCII text file you are writing to and not a mat file. E.g.,

save(tempname1, 'stations', '-append', '-ascii')

[Matteo Niccoli]

HI James, thanks for your answer. if I do as you suggest, I do not get the error, but I do get a warning:

Warning: Attempt to write an unsupported data type to an ASCII file.
  Variable 'stations' not written to file.

So I still do not get the desired result. Is it not possible to append strings? Any suggestions about this?

[James Tursa]

Yes, it appears save will convert your string to numeric and then write that out. You may have to resort to fwrite for this. E.g.,

fid = fopen(tempname1,'at'); open in append ASCII text mode
fwrite(fid,stations,'*uchar'); % append the string as character data
fprintf(fid,'\n'); % append a newline
fclose(fid); % close the file

Or you may need to wrap a loop around the fwrite and fprintf if stations is a cell array of strings and you want to print one string per line, etc.