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

Question

Jingyu Ru 2015-11-3

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https://ww2.mathworks.cn/matlabcentral/answers/252448-after-using-the-datastore-function-how-to-change-the-value-in-the-csv

编辑： Jingyu Ru 2015-11-4

采纳的回答： Aaditya Kalsi

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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

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Answer 1

Aaditya Kalsi 2015-11-3

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在 MATLAB Online 中打开

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.

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Jingyu Ru 2015-11-4

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?

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