CODEWITHSUNDEEP
matlaboop
Tom S
Tom S

Reputation: 135

'Find' and 'unique' in an array of user-defined class objects (MATLAB)

After dabbling in C# I'm now keen to use some OOP in Matlab - to date I've done none!

Let's say that I define a class for a data object with a handful of properties...

classdef TestRigData
    properties
        testTemperature
        sampleNumber
        testStrainAmplitude
        sampleMaterial
        rawData
    end

    methods
        % Some constructors and data manipulation methods in here
    end
end

...where 'rawData' would be a m-by-n array of actual experimental data, and the other values being doubles or strings to help identify each specific experiment.

If I have an array of TestRigData objects, what would be the best way of finding the indices of objects which meet specific criteria (e.g. testTemperature == 200)? Or getting all the unique values of a property (e.g. all the unique sample numbers in this collection).

If they were arrays of their own, (myNewArray = [3 5 7 22 60 60 5]) it would be easy enough using the find() and unique() functions. Is there a class I can inherit from here which will allow something like that to work on my object array? Or will I have to add my own find() and unique() methods to my class?

Upvotes: 0

Views: 515

Answers (2)

Tom S
Tom S

Reputation: 135

The suggestion of creating this as a handle class (rather than value class) is something I need to think about more in the future... after having put together some initial code, going back and trying to change classdef TestRigData to classdef TestRigData < handle seems to be causing issues with the constructor.

Bit unclear of how I would go about using a hash value unique to each object... but the syntax of extracting all values to an array is ultimately what got me in the right direction.

Getting a new object array which is the subset of the original big data array conforming to a certain property value is as easy as:

newObjectArray = oldObjectArray([oldObjectArray.testTemperature]==200);

Or for just the indices...

indicesOfInterest = find([oldObjectArray.testTemperature]==200);

Or in the case of non-scalar values, e.g. string property for sample material...

indicesOfInterest = find(strcmpi({oldObjectArray.sampleMaterial},'steel'));

Upvotes: 0

Eitan T
Eitan T

Reputation: 32930

You can assign an ID value (a hash value in the general case) to TestRigData objects and store it as a new property. You can then extract all ID values at once to a cell array, e.g {yourarray.id} (or [yourarray.id] if the ID values are scalars), allowing you to apply find and unique with ease.

Adding your own find and unique is definitely possible, of course, but why make life harder? ;)

Upvotes: 2

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