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    %% Write and Reconstruct Tall Array
% Write a tall array to disk, then subsequently recover the tall array by
% creating a new datastore for the written files. This process is useful to
% save your work or share a tall array with a colleague.

%%
% Create a datastore for the |airlinesmall.csv| data set. Select only the
% |Year|, |Month|, and |UniqueCarrier| variables, and treat |'NA'| values
% as missing data. Convert the datastore into a tall table.
ds = datastore('airlinesmall.csv');
ds.TreatAsMissing = 'NA';
ds.SelectedVariableNames = {'Month','Year','UniqueCarrier'};
tt = tall(ds)

%%
% Sort the data in descending order by year and extract the top 25 rows.
% The resulting tall table is unevaluated.
tt_new = topkrows(tt,25,'Year')

%%
% Save the results to a new folder named |ExampleData| on the |C:\| disk.
% (You might want to specify a different write location, especially if you
% are not using a Windows(R) computer.) The |write| function evaluates the
% tall array prior to writing the files, so there is no need to use the
% |gather| function prior to saving the data.
location = 'C:\ExampleData';
write(location,tt_new)

%%
% Clear |tt| and |ds| from your working directory. To recover the tall
% table that was written to disk, first create a new datastore that
% references the same directory. Then convert the datastore into a tall
% table. Since the tall table was evaluated before being written to disk,
% the display now includes a preview of the values.
clear tt ds
ds2 = datastore(location);
tt2 = tall(ds2)