MATLAB: Does matlab save strings from delimited text file as individual characters? And how to prevent.

numbersstringsplit

So, I have a cell structure in Matlab (containing words, dates and numbers separated by ";" loaded from a very large file) which I take certain lines from, then do some calculations on and finally write each field to a separate file as a table (the words being the headers, the dates and numbers the data).
I have the script functioning more or less okay, be it that I keep running into a particular problem; namely that when splitting the lines using strsplit all entries are treated as individual characters. So when I select a cell entry and add a position, for example A.a{1,1}(2) it returns the second letter of the string. It also does this for numbers, making manipulation difficult. Being splitted strings Matlab treats multi-digit numbers as single numbers, so when I do A.a{1,2} it returns 122, but when I do A.a{1,2}*2 I get ans = 98 100 100 rather then 244. Now I could use str2num, but that doesn't work for words or dates so can become pretty cumbersome… I have a hard time finding the right command to convert all entries to single 'words'. I've also tried using cell2array and array2table commands, but I somehow keep running into issues. Any help would be appreciated!

Best Answer

Rather than wasting time importing the data as character, you would be much better of using textscan to import numeric values as numeric data, for example this reads your entire example file:
opt = {'Delimiter',';', 'CollectOutput',true};
fid = fopen('merged.txt','rt');
hdr = fgetl(fid);
fmt = ['%s',repmat('%f',1,nnz(hdr==';'))];
C = textscan(fid,fmt,opt{:});
fclose(fid);
and checking:
>> size(C{1}) % the number of date strings
ans =
   6076      1
>> size(C{2}) % the size of the numeric matrix
ans =
   6076     47
>> C{1}{[1,end]} % the first and last dates
ans = 07-09-2017 08:25:33
ans = 07-09-2017 10:40:54
" I work with a 200M+ lines file"
If you have a very large file that cannot be imported at once then you can adapt the code I have shown above using the method given in the MATLAB documentation, which reads blocks of data at-a-time:
https://www.mathworks.com/help/matlab/import_export/import-large-text-files.html
Basically the trick is to use the third optional input to specify how many lines to read, and call textscan in a loop.
Related Question