www.gusucode.com > matlab 案例源码 matlab代码程序 > matlab/ReadAndAnalyzeDataInAKeyValueDatastoreExample.m
%% 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)