After using the datastore function, how to change the value in the 'csv' ?

I find it is useful to read the 'csv' file with the datastore function. Especially for the big data.

After analysis the data, I want to change some value in the 'TabularTextDatastore' data. What function could I use?

For example:

code:

ds = datastore('airlinesmall.csv','TreatAsMissing','NA',... 'SelectedVariableNames','ArrDelay','ReadSize',1000);

sums = [];

counts = [];

while hasdata(ds)

    T = read(ds);

% change the year value less than 1997 to 0 %

end

Answer 1

[Aaditya Kalsi]

The datastore cannot reflect the changed values because it simply reads the data from the file into a table.

If you want to store the changed values, you want to write the modified table back out.

Example:

while hasdata(ds)
    [T, info] = read(ds);
    T.DateValue(T.DateValue < 1997) = 0;
    filename = ['newfolder/newfile_', num2str(info.Offset), '.txt'];
    writetable(T, filename);
end

newds = datastore('newfolder/*.txt');

While this may not be the most efficient, it certainly will work.

Hope that helps.

[Jingyu Ru]

Thank you for your helping. Do you mean in this 'datastore' framework or even in this release of Matlab, I have to save every partition csv/txt files respectively and assemble them together using other software after analyzing all the data?