create csv files by extracting data from a starting csv file

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Giuseppe D'Amico 2020-10-30

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评论： Walter Roberson 2020-11-3

Hi everyone, I am writing to you as not being familiar with matlab I do not know the commands and I would need your help to create a script.

I have a large csv file that cannot be opened with excel, within this file there are many lines that are composed of both numbers and letters, within these lines there are codes formed by letters and numbers (eg UPRE 14234) that identify the element that interests me and to which they belong, in total there are 21 different UPRE codes.

What I would like is to divide the initial csv file into 21 csv files each composed with the lines concerning only one of those UPRE codes.

How can I do? Can anyone tell me what functions to use and how to write the script?

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Walter Roberson 2020-10-30

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I suggest you work with lower level utilities:

grep or egrep if you are using Mac or Linux
findstr or select-string if you are using MS Windows

https://stackoverflow.com/questions/1416241/is-there-a-pattern-matching-utility-like-grep-in-windows

These will be much more efficient than the equivalent MATLAB code.

Another option is to make use of the fact that Perl is shipped with MATLAB.

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Walter Roberson 2020-11-2

I managed to upgrade my Windows to the latest release and all the other update housekeeping tasks (except I didn't finish defragmenting the drive) . I managed to install Mac OS Catalina and use that to download all of the Mac and Windows install files and install R2020b on Catalina, which gives me the files I need to flip over to Windows to install R2020b. So I have everything ready.

... but by then it was close to 4am so I started playing a game that I had been waiting on for the last year, as it needed Catalina and I had always been too busy answering questions to install Catalina before.

Walter Roberson 2020-11-3

在 MATLAB Online 中打开

The below is tested.

Please note that you will need to add all strings that you want searched for into the UPREs cell array, and you must use exact matches.

The command that is created is quite sensitive to which quotes are used and how many are used. The rules for quoting strings in MS Windows are not well documented, and are quite different from Unix. The rules for handling double-quotes are particularly strange.

This code expects a text file, not a .xlsx file.

infile = 'exp_misure_prelievo.txt';
outdir = 'UPRE_files';
UPREs = {'UPRE_S14SPLO_901', 'UPRE_S14LCRN_901'};
if ~exist(outdir, 'dir'); mkdir(outdir); end
for K = 1 : length(UPREs)
    this_UPRE = UPREs{K};
    outfile = fullfile(outdir, [this_UPRE '.txt']);
    cmd = sprintf('FINDSTR "|"""%s"""|"  "%s" > "%s"', this_UPRE, infile, outfile);
    [status, result] = system(cmd);
    if status ~= 0
        fprintf('Problem processing %s, output was:\n', this_UPRE);
        fprintf('%s\n', result);
    end
end
fprintf('Done\n');

I had to do a lot of work to get to the point of being able to debug this problem. I only boot Windows every few months, and it turned out to be a truly remarkable amount of work to get my Mac to share some files with Windows.

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Jon 2020-10-30

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Without knowing all of the details of what is in your files it is hard to give a specific answer. However for general advice I would suggest using the matlab function readcell. This will read the entire file into a cell array. You can then work with the data in that cell array relatively easily indexing by rows and columns. Maybe you can do the processing you want on this overall cell array and it isn't even necessary to create many smaller csv files unless you need them for some other task.