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    %% Read and Analyze MAT-File with Key-Value Data
% This example shows how to create a datastore for key-value pair data in a MAT-file that is the
% output of |mapreduce|.
% Then, the example shows how to read all the data in the datastore and sort it. This example assumes that
% the data in the MAT-file fits in memory.
%%
% Create a datastore from the sample file, |mapredout.mat|, using the
% |datastore| function. The sample file contains unique keys representing
% airline carrier codes and corresponding values that represent the number
% of flights operated by that carrier.

% Copyright 2015 The MathWorks, Inc.

ds = datastore('mapredout.mat');
%%
% |datastore| returns a |KeyValueDatastore|. The |datastore| function
% automatically determines the appropriate type of datastore to create.
%%
% Preview the data using the |preview| function. This function does not
% affect the state of the datastore.
preview(ds)
%% 
% Read all of the data in |ds| using the |readall| function. The
% |readall| function returns a table with two columns, |Key| and
% |Value|. 
T = readall(ds)
%%
% |T| contains all the airline and flight data from the datastore in
% the same order in which the data was read. The table variables, |Key| and |Value|, are
% cell arrays.
%%
% Convert |Value| to a numeric array.
T.Value = cell2mat(T.Value)
%%
% Assign new names to the table variables.
T.Properties.VariableNames = {'Airline','NumFlights'};
%%
% Sort the data in |T| by the number of flights.
T = sortrows(T,'NumFlights','descend')

%%
% View a summary of the sorted table.
summary(T)
%%
% Reset the datastore to allow rereading of the data.
reset(ds)