How to Deal with a jdbc4array?

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Peter Brady
Peter Brady 2015-7-26
回答： Piyush Kumar 2024-11-28
Hi,
I think my question is similar to: http://au.mathworks.com/matlabcentral/answers/83678-accessing-postgressql-time-interval-data but that comment is not working for me.
Like that post I'm using the Database Toolbox to retreive data from a PostgreSQL database via the Postgre JDBC connector and I can also access the vast majority of the "normal" data returned in the query.
My problem is that I have an array of data, in this case it happens to be a time series of double precision, that is returned as an object of class jdbc4array.
I'm not so good with java and the only way I've figured out to extract the elements is with code something like the following:
curs = exec(conn, query);
curs = fetch(curs);
events = curs.Data;
rainFall = cell2mat(eval(events{1, 21}))
My problem is that while the above commands work and successfully extract the values from the jdbc4array into a MATLAB array that I can then process as normal the "eval" operation is computationally expensive. Can anyone suggest a better method to extract the java array into a MATLAB array. The project I'm working on is looking to run hundreds of thousands of events and my profile results indicate that the eval operation is consuming about 80% of the run time - there has to be a better way.
Thanks in advance.
Peter Brady

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回答（1 个）

Piyush Kumar
Piyush Kumar 2024-11-28
Ran in:
Hi,
To handle a jdbc4array in MATLAB more efficiently, you can directly convert the Java array to a MATLAB array using Java methods. For example,
% Create a Java array of doubles
jdbcArray = javaArray('java.lang.Double', 5);
for i = 1:5
jdbcArray(i) = java.lang.Double(i * 1.1);
end
% Display the Java array
disp('Java Array:');
Java Array:
disp(jdbcArray);
java.lang.Double[]: [1.1000] [2.2000] [3.3000] [4.4000] [5.5000]
% Initialize a MATLAB array
matlabArray = zeros(1, length(jdbcArray));
% Convert the Java array to a MATLAB array
for i = 1:length(jdbcArray)
matlabArray(i) = jdbcArray(i);
end
% Display the MATLAB array
disp('MATLAB Array:');
MATLAB Array:
disp(matlabArray);
1.1000 2.2000 3.3000 4.4000 5.5000

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