For Loop: How to add string to matrix?

Hi everyone,

I am new to Matlab, and I think I am on my way with this first problem but having a few issues.

Here is what my original data looks like...

INDEX	TRACK NUMBER	UTC DATE	UTC TIME	LOCAL DATE	LOCAL TIME	LATITUDE	N/S	LONGITUDE	E/W	ALTITUDE	SPEED
1	1	1/05/2019	21:21:25	2/05/2019	10:21:25	36.28896	S	174.806381	E	0.196573	0.504
2	1	1/05/2019	21:21:30	2/05/2019	10:21:30	36.288898	S	174.806412	E	-10.27161	0.144
3	1	1/05/2019	21:21:46	2/05/2019	10:21:46	36.288879	S	174.806396	E	-0.534371	0

To this, I want to remove all columns except for 'Local Date', 'Local Time', 'Latitude' and 'Longitude'.

I also want to add a column called 'CallSign' in which all the rows will be filled with the word 'CallSign'.

This is working fine for lat/long, for these two columns I only adjust latitude by multiplying by -1 to get correct values.

My difficulties:

-how to add a word 'Callsign' to every row of that column, which seems like a simple problem...?

-how to convert date to datenum and time to datenum, do they need to be together in one column first? Or can they be converted separately?

-how to add column headers to my output file.

dd = 'input_data';
nowd = cd;                  %current folder
cd(dd);                     %go to input folder
d = dir('*.csv');
cd(nowd)                    %GO BACK TO current folder

                                                                        %d=dir(fullfile(dd, '*.csv'));

                                                                           
for j = 1:length(d)
tic                                                                        %tic starts a stopwatch timer, tic saves current time that TOC uses later to measure time elapsed between the two
                                
    filename = d(j).name;                                                  %get name of file (d.name) of jth iteration
    disp(filename);                                                        %show filename
    try                                                                    %begin a 'try' block. 
    fid = fopen(fullfile(dd,filename));                                    %fopen opens file for access, fullfile builds filename from parts
    
    
    %%make empty matrices for each variable
                                        
    callsign = zeros(length(lines),1);                                        %lines gives length of 64 (from default colourmap) -just a quick way of getting lots of rows?                                                                        %1 represents number of columns
    londecdeg = zeros(length(lines),1);
    latdecdeg = zeros(length(lines),1);
    date = zeros(length(lines),1);
    time = zeros(length(lines),1);

    
    tline = fgetl(fid);                                                    %fgetl returns next line of file associated with file identifier (fid)
    i=1;
    
    
    %% for each csv file add callsign, convert latdecdeg, date and time    %convert to number format
    while(1)
        try
        tline = fgetl(fid );
        if( ischar(tline) == false )                                       %ischar to find out if input is a character array
            break;
        end
        
        c = strsplit(tline,',');                                           %strsplit splits tline ('next line') at delimiter ',' into c
        
       callsign(i) = str2double(c{1}); fill values column with "Callsign"   %str2double converts all rows(?) of column 4 to number format

        londecdeg(i) = str2double(c{9})                                  

        lat =  str2double(c{7});                                          %conver lat to number format and then to decimal degrees
        latdecdeg(i) = lat*(-1)                                

         try                                                                
         date(i) = datenum(c{5},'dd-mm-yyyy');                       %convert date to datenum
         catch 
             date(i) = NaN;                                                     
         end
         i=i+1;
         catch
             disp('while loop error');
        end
    end

    %% Create Output
    out = [date, time, callsign, latdecdeg, londecdeg];

    outFileName = strcat('DATENUM_TIME_CALLSIGN_LAT_LON',num2str(j),'.csv');  %labels each file with the same name and concatenates with a diff. number at the end of each
    dlmwrite(fullfile('output',outFileName),out,'precision',15);
    catch
        disp(['ERROR!!!!!! ' filename])
    end
    toc
end

[KSSV]

This should be more simple..if you read the data as a table. Read about readtable.

[Louise Wilson]

Thank you, it does seem like it should be very simple. Surely there is a way? Can I do all of my other steps if the data is a table?

[Louise Wilson]

The problem to my first question was resolved here:

callsign = zeros(length(lines),1);  

by changing zeros to strings, to mark text.

This works now! But now none of my data will export correctly to a .csv file. Presumably because I have changed one column to text? I'm not sure though because .csv file support text and I would like to keep text in.