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For Loop: How to add string to matrix?

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Louise Wilson
Louise Wilson on 8 May 2019
Commented: Louise Wilson on 8 May 2019
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

  3 Comments

KSSV
KSSV on 8 May 2019
This should be more simple..if you read the data as a table. Read about readtable.
Louise Wilson
Louise Wilson on 8 May 2019
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
Louise Wilson on 8 May 2019
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.

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