Getters and Setters Within an Object - matlab

Question

I have an object called TestData() that handles data processing and places it in a file in a specified format. One of the properties is data, which is stored as an array of type double. Here is the object and its constructor:
classdef TestData
properties
metaData = []; % stores meta data in Nx2 array
data = []; % stores data in PxQ array
colLabels = []; % labels columns
colUnits = []; % provides units
metaPrint % used to print metaData
temp % debugging purposes only
end
methods
%****************************************************************************%
%Function: TestData
%Purpose: Constructor used to allocate data arrays
%****************************************************************************%
function this = TestData() %constructor
this.metaPrint = [];
this.temp = [];
end %TestData()
The data that is placed into the object comes from a .m file external to the object, like so:
myTestData=TestData; % Generate an instance of the object
% Data
ErrorLine1 = zeros([length(ErrorLine')+2 1]); % Empty Vector to store 11X1
ErrorLine data
ErrorLine1(2:end-1) = ErrorLine(1:end);
mat = [Avec' Bvec' Invec' Ovec' ErrorLine1 PercentErrorOD'];
myTestData.data = mat;
So, when I set myTestData.data = mat this places the data in the object, but then calls the getter and setter functions for that object. One of the principle reasons for using these functions is to filter the data and determine if it is the correct type of data (in this case, the format would need to be double). When I try this in the code, however, it doesn't seem to work. Here is what I have written for the getter:
function data = get.data(this)
data = this.data;
end %getData
And the setter:
function this = set.data(this, data)
i = arrayfun(#(n)strcmp(class(this.data(n)), 'doube'), 1:numel(this.data)); %#ok<STISA>
disp(i)
if any(i == 0)
disp("WE HAVE A ZERO")
msg = "Data in object's 'data' property is not of type double";
error(msg);
else
this.data = data;
disp('Hi from setter')
end
end % set.data
If I run the strcmp and any functionality through the command window it works! When I run it from the editor, though, it always displays the "Hi from setter" string, even if I change "double" in the compare to "string." So, I am just not sure why it is not entering the if statement.
If there is anything that you can see in my code that could be modified to make it more efficient please let me know. Also, if there is anything else I can do my best. Thanks in advance!

Answer 1

In your setter, you have this line:
i = arrayfun(#(n)strcmp(class(this.data(n)), 'doube'), 1:numel(this.data));
But note that here you have not yet done this.data = data. When you test this.data, you test the old value of the property, not the value you want to assign. You need to test data.
Instead of using strcmp on the result of class, you can better test with isa. Furthermore, unless data is a cell array or a struct array, each of the elements will always be of the same class. You don't need to iterate over the whole array to test its type, just look at the type of the array itself. In the case of the cell array and the struct array, the indexing has to be different to extract elements. So, data(n) will always have the same type as data. Thus your setter can be written as:
function this = set.data(this, data)
if ~isa(data,'double')
error('WRONG!')
end
this.data = data;
end
Another issue with the code: if any(i == 0). any collapses one dimension of the input array. So if i is a 2D matrix, then the output is a row vector. Each element will be true if any of the elements in the given column is true. The if statement is only true if all elements of the given expression are nonzero. That means that all columns must have at least one 0 value for this expression to trigger.
Instead, do if any(i(:)==0). Here we make i into a column vector (this doesn't copy data, it's efficient), and thus any will return a single (scalar) value. If you have MATLAB R2018b, then you also do if any(i,'all'), which is equivalent.
You'll often see code doing if any(any(i==0)), but this fails if i happens to have three or more dimensions. It is also inefficient, the forms above are better.