MATLAB: How to solve preallocating speed of a variable

class objectmethodsobject variableobject-orientedoopproperties

I have a variable which is object structure, I mean I define all properties in an m.file classfile and properties structure. Then I use them with a variable for example;

classdef obj<handle> 
    properties
        id = zeros;
    end
end

Then, I use for example "car" list in the for loop to fill the all properties, the number of properties is 30.

car = [];
for segment=1:5
    for brand = 1:6
        car(segment,brand).id = list(brand,'id');
        ..... till 30 properties like above
    end
end

It works but the MATLAB gives suggestion to speed the script. The error*;

*The size of the indicated variable or array appears to be changing with each loop iteration. Commonly, this message appears because an array is growing by assignment or concatenation. Growing an array by assignment or concatenation can be expensive. For large arrays, MATLAB must allocate a new block of memory and copy the older array contents to the new array as it makes each assignment.

*Programs that change the size of a variable in this way can spend most of their run time in this inefficient activity. There is also significant overhead in shrinking an array on each iteration or in changing the size of a variable on each iteration. In such cases, MATLAB must reallocate and copy the contents repeatedly.

*For scripts, Code Analyzer cannot determine whether the array was preallocated before the script was called. Depending on your use of scripts, you might want to enable or disable this message independently of the related message (with message ID AGROW) that applies to functions and class methods.

How to make this done, variable has two indices like car(segment,brand).

Best Answer

One simple solution is given here:

https://www.mathworks.com/help/matlab/matlab_oop/creating-object-arrays.html

"To preallocate the object array, assign the last element of the array first."

You will have to make sure that your class returns a default value.

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MATLAB: How to display result of the program in a table GUI

Hi,

Just check the uitable function.

A sample for uitable creation is below:

hfig = figure; % this will be your GUI figure or where you want to put your table  
tHandle = uitable(hfig,'Data',area,'Position',[xPixel yPixel Width Height]); 
% xPixel yPixel are the coordinates of the table according to your screen resolution.
% Width and Height are the sizes of your table respectively.

Here is the link: uitable

I have created one by one struct arrays and a cell array which contains those struct arrays.

You can look the example below how to extract them.

Edit to extract Structs:

%% Struct Arrays Definitions 
% cities is the struct array just like your area array's first element.
cities(1).Name = 'London';
cities(2).Name = 'Paris';
cities(3).Name = 'Madrid';
cities(1).Population = '30000';
cities(2).Population = '40000';
cities(3).Population = '50000';
cities(1).AverageAge = '30';
cities(2).AverageAge = '35';
cities(3).AverageAge = '40';
% cars is another struct array just like your area array's second element. 
cars(1).Brand = 'Porche';
cars(2).Brand = 'Lamborghini';
cars(3).Brand = 'Maserati';
cars(1).Model = '2010';
cars(2).Model = '2011';
cars(3).Model = '2012';
cars(1).Color = 'Pink';
cars(2).Color = 'Blue';
cars(3).Color = 'Black';
%% Cell Array Creation from the Struct Arrays above
array{1} = cities;
array{2} = cars;
% array is a 1x2 cell array contains struct arrays each cell. 
%array is like your area array. 
%% Extracting Structs from the array's each cells and put them together vertically
TableData     = {};
tableRowNames = {};
for i=1:numel(array)
   TableData = [TableData; squeeze(struct2cell(array{i}))]; % you can also use horzcat or comma (,) instead of (;) to put them horizontally.
   tableRowNames = [tableRowNames;fieldnames(array{i})]; % creation of table rownames to be used in the future.
end
% Creating Figure
hfig = figure('units','normalized','Position',[0.1 0.1 0.7 0.7]); 
xPixel = 0.1; yPixel = 0.1; Width = 0.8; Height = 0.7; % definitions of pixels positions of table
% Creating Table
tHandle = uitable(hfig,'Data',TableData,'units','normalized','Position',[xPixel yPixel Width Height]);
tHandle.RowName = tableRowNames; % put table row names

But it would be much more easier for us to see your data type what it contains and what kind of output you would like to see as a result with a real example.

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