I've created an object with an Id property.
I'm trying to create an array which will automatically fill the Id property according to the location in the array or a static incrementing int starting from 1.
How do I implement this?
I tried to create a constructor with id as input, but writing
myArr(100) = myObj throws an error.
How do I initialize this also with the id (using static id or any other way).
Thanks
I know this is only a partial solution, but suppose you have a matrix M where the first index is the ID value, then here is what you can do:
M(:,1) = 1:size(M,1)
Or if you have a matrix M where the first column needs to be added with ID values:
M = [1:size(M,1) M]
classdef a_class < handle
properties
id
end
methods
function obj = a_class(size_of_matrix)
if nargin == 0 %default constructor
%something constant. Do not try to place counter here.
else
if numel(size_of_matrix)==1
size_of_matrix = [size_of_matrix size_of_matrix];
end;
obj(size_of_matrix(:)) = a_class; % Preallocate object array
id_cell = num2cell(1:prod(size_of_matrix));
[obj(1:prod(size_of_matrix)).id] = id_cell{:};
end
end
end
end
I'm afraid, this is the best possible solution.
Note you can't define a counter in default constructor, and then allocate an array, as, in fact, it would be called only once.
PS
They use even more naive for-based syntax in official tutorial...
Related
Hi everyone i'm experiencing some trouble with my code. The goal is to add multiple objects to a class, i've created the following code for that:
array = cell(1,10);
A = matrix %specified somewhere else
for ind = 1:10
[r c] = find(A<3);
random = randi([1, size(r,1)]);
array{ind} = classname(1, r(random), c(random));
end
This block of code does everything I want it to, however, later on I add this array as property to another class and have to work with that specific array to make changes to it. And that is where is goes wrong.
function growing(thisElement)
for i = 1:length(otherClass.array)
range = range((otherClass.array(i).locationX - 2), (otherClass.array(i).locationX +2));
if otherClass.array(i).pos<20
......
end
end
end
Whereby both locationX and pos are properties of classname. I get the error Dot indexing is not supported for variables of this type. For both the range as the last if part. The error is apparently very commen error, however, I don't find any answers relating my case. Has anyone an idea to bypass the error?
My task:
Create 2 class objects. Delete all elements in the first object that are contained in the second.
My implementation:
class Vector
def initialize
#vector = Array.new
end
end
vector1 = Vector.new(1,2,3,4,5,6,7)
vector2 = Vector.new(3,6,7)
But this does not work as needed. What should I fix?
I think it is some sort of question from institute, and requirements are different than what you coded, I am just trying to correct your coding and rectify so you get some result, than you can further proceed to full-fill your requirements.
Your first mistake is you are asking for one parameter but providing
commas is giving multiple parameters, so I have changed it to get
array.
As changed array so now you can't add another array in first, as it
is just one array so I am removing << and adding = in initialize
method
Your initialize method is not taking any parameter, but you are
providing, but you have to define a method set_vector so you have
to use that method instead of class, as per your requirement that is
what you want.
You should define - method but than you have to play with class
variables too, as you are playing with two object and with in your
class you have to define - function, but I am here just using your
get_vector method to compare arrays and return your response.
changing put to print so you can have variables instead of all items.
Hope this will give you some helpful insight to coding.
class Vector
def initialize
#vector = Array.new
end
def set_vector=(vector)
#vector = vector
end
def get_vector
#vector
end
end
def confront(first_vector, second_vector)
first_vector.get_vector - second_vector.get_vector
end
first_vector = Vector.new
first_vector.set_vector=[1,2,3,4,5,6,7]
second_vector = Vector.new
second_vector.set_vector=[3,6,7]
final_vector = confront(first_vector, second_vector)
begin
puts "First:"
print first_vector.get_vector
puts "\nSecond:"
print second_vector.get_vector
puts "\nFinal Vector:"
print final_vector
end
this is my first question so i hope I am doiung the tagging and so on right.
I have an array of objects of the same class. When I want to access a property of the objects I can use:
Data = [ObjectArray.property];
Now I want to call a mehtod of the class for each object and get back the result as Vektor/ matrice:
result = [ObjectArray.myfun(X)]
here I get an error saying:
Expected one output from curly brace or dot indexing expression
I tried brute force several different annotation but nothing works and i can't find a solution online.
Anybody knows how to make this work?
Thanks and Cheers!
It's slightly unclear what the structure of your array is, but you should be able to use arrayfun.
result = arrayfun( #(obj) obj.myfun(x), ObjectArray );
If you function myfun returns anything other than a scalar, you will need to set the UniformOutput flag to be false. This will make the result a cell array, with one cell per result.
result = arrayfun( #(obj) obj.myfun(x), ObjectArray, 'uni', false );
% If you want to concatenate results, could use something like
% result = [result{:}];
Note that this is basically shorthand for a loop, but it saves you pre-allocating an output and writing the loop.
You can also do this directly inside of your myfun:
If the item you operate your method on is an array, the first parameter of your myfun method will be an array. This can be used, and call itself one by one:
vec = [MyClass(1), MyClass(2)];
list = vec.myfun();
classdef MyClass
properties
prop1
end
methods
function obj = MyClass(val)
obj.prop1 = val;
end
function val = myfun(obj)
if numel(obj) > 1
val = arrayfun(#(o) o.myfun(), obj);
return;
end
val = obj.prop1;
end
end
end
I have a class constructor that takes multiple numeric arrays of the same size and creates an object array of the same size. In the constructor, I am trying to use deal to assign data from each input array to a single index of the object array's only property:
classdef myClass
properties
data
end
methods
function obj = myClass(varargin)
nArg = length(varargin);
for iArg = 1:nArg
dataArg = num2cell(varargin{iArg});
[obj.data(iArg)] = deal(dataArg{:});
end
end
end
end
Unfortunately, I get the following error from deal: The number of outputs should match the number of inputs.
I believe that this is probably occurring because I haven't preallocated the object array before the for loop in the constructor, e.g.:
szObj = size(varargin{1});
cellSzObj = num2cell(szObj);
obj(cellSzObj{:}) = myClass.empty;
However, for various reasons, I want to be able to make this assignment without preallocating the object array.
Is there a way to do this?
how do I extract an array of object properties from an object array (where each of the objects within that array has that property?)
Ex.:
classdef myClass
properties
myProperty = 1
end
end
--
myObjectMatrix(1:1000) = myClass()
myObjectMatrix(100:234).myProperty % what I thought would work but results in lots of individual results
[myObjectMatrix(100:234)..myProperty] works, but only in one dimension. I need to use reshape() if I have more than one dimension to 'fold' my results back.
Is there a better way?
Thanks!
Basically that code would act on each member in turn and return a separate answer, so in the end you only get a 1x1 output.
The solution in that example is to use arrayfun(), such as:
myObjectMatrix(1:1000) = myClass()
output = arrayfun(#(x) x.myProperty,myObjectMatrix(100:234))
That would give you a 1x135 array containing the value of each of the myProperty member from each of the elements selected from the class array.
In arrayfun you give a function to perform on each element in the array and then the array to act on. In this case I created an anonymous function which simply accesses myProperty on x - where x will be each object in the array in turn.
It is important to note that the above will only work if the property is a single value, not a matrix/array. If it is an array then the output will be nonuniform, and you will have to do:
output = arrayfun(#(x) x.myProperty,myObjectMatrix(100:234),'UniformOutput', false)
In this case 'output' will be a cell array containing the value of the property of each class.