I'm trying to understand the behavior of a class while passing arguments. The basic concept of a class is that it captures a data array along with information about the dimensions--so the sample class I have describes position and time information along with the data.
I began noticing this behavior when I started writing what I've referred to as "smart" indices for the data. So instead of calling the data field myIntensity.data and providing logical or numerical indices, I can call myIntensity.smartData and provide numbers or ranges that correspond to my position/time vectors within the class. I also want the user to be able to use MATLAB's normal indices with this smartData function, so my full class (skeleton below) also supports arguments like ':' and end.
The behavior I'm confused about is what happens when I use the 'end' argument. If I step through the smartData function, it will first catch on line 22 (if ~exist('x','var')), set my output value to all data, and return. However, it will then step into smartData a second time, except this time with the argument corresponding to 'end' set to the length of the corresponding dimension of the data I just returned. This is also true if not all input arguments are provided: e.g. if a previous argument is left out, the 'end' index argument will equal the length of the earlier dimension corresponding to its order in the arguments provided.
My question: why does MATLAB make a second function call? Does this reproduce on other machines/versions (mine: R2013b on 64-b Windows 7 Enterprise)? Can I rely on this behavior, or is it an artifact of my set-up and something I should warn the user about?
Sample code producing results described:
x = -5:5; y = 3.28:0.01:3.46; z = [0 2 6 8 10 12 16 18 20];
time = 0:0.1:20; data = zeros(length(x),length(y),length(z),length(time));
newIntensity = intensity(x,y,z,time,data);
myData = newIntensity.smartData(0,[3.3 3.35 3.4],[0 10 20],end);
-> myData returned corresponds to expected index, only after stepping through smartData function twice
classdef intensity
properties
x = [];
y = [];
z = [];
time = [];
data = [];
end
methods
function obj = intensity(x,y,z,time,data)
obj.x = x;
obj.y = y;
obj.z = z;
obj.time = time;
obj.data = data;
end
function val = smartData(obj,x,y,z,time)
if ~exist('x','var')
val = obj.data;
return;
end
xInds = obj.getSmartInds(obj.x(:),x(:));
yInds = obj.getSmartInds(obj.y(:),y(:));
zInds = obj.getSmartInds(obj.z(:),z(:));
timeInds = obj.getSmartInds(obj.time(:),time(:));
val = obj.data(xInds,yInds,zInds,timeInds);
end
end
methods (Access = private)
function indsOut = getSmartInds(~,list,indsIn)
if all(indsIn >= min(list)) && all(indsIn <= max(list))
indsOut = dsearchn(list,indsIn);
else
indsOut = indsIn;
end
end
end
end
Thanks for your help.
