Creating discrete variables within a for loop

I'm trying to do something like the following:

for i = 1:n
H(i) = [0 1 1 0 ; 0 0 1 1];
end

Essentially I'm trying to create multiple shapes in a for loop, each shape with it's own distinct handle. This imaginary code above would create n squares with handles H1, H2, ... all the way to Hn. I know that this syntax is not correct, but I'm wondering if there is any function in matlab that behaves this way? I want to be able to alter the coordinates of each shape individually, but also move them as a group, something like:

for j = 1:n
H(j) = H(j) + 1
end

This would move all of the shapes by 1 in the x direction and 1 in the y. Again, this is not the right syntax, but you get the idea. Anyone know of a way to create discrete shapes and alter them within a for loop?

Answer 1

[Cedric]

UPDATED

Here is a fun (maybe) example:

 nShapes = 10 ;
 nFrames = 100 ;

 % - Build figure and axes.
 figure() ;
 set( gcf, 'Units', 'normalized', 'Position', [0.1, 0.1, 0.6, 0.8] ) ;
 set( gca, 'XLim', [-15, 15], 'YLim', [-15, 15] ) ;
 grid on ;

 % - Add shapes.
 H = cell( nShapes, 1 ) ;
 for shapeId = 1 : nShapes
    P0 = 20 * rand( 1, 2 ) - 10 ;
    H{shapeId} = patch( P0(1)+[0, 1, 1, 0], P0(2)+[0, 0, 1, 1], 'b' ) ;   
 end

 % - Define rotation matrix.
 theta = -2*pi / nFrames ;
 R = [cos(theta), -sin(theta); sin(theta), cos(theta)] ;

 % - Move.
 for frameId = 1 : nFrames
    for shapeId = 1 : nShapes
        H{shapeId}.Vertices = H{shapeId}.Vertices * R ;
    end
    pause( 0.1 ) ;
 end

[Cedric]

Now here is an updated version for Star Strider ;-)

 nShapes = 40 ;
 nFrames = 100 ;

 % - Build figure and axes.
 figure() ;
 set( gcf, 'Units', 'normalized', 'Position', [1.1,0.1,0.6,0.8] ) ;
 set( gca, 'XLim', [-12,12], 'YLim', [-12,12] ) ;
 grid on ;

 % - Define the pacman function.
 pacman = @(x, y, varargin) patch( bsxfun( @plus, x(:)', 0.5*[0,cos(-3*pi/4:0.1:3*pi/4),0]' ), bsxfun( @plus, y(:)', 0.5*[0,sin(-3*pi/4:0.1:3*pi/4),0]' ), varargin{:} ) ;

 % - Add pacmans.
 P0 = 20 * rand( nShapes, 2 ) - 10 ;
 h = pacman( P0(:,1), P0(:,2), [1,0.8,0.3], 'EdgeColor', [0,0,0] ) ;

 % - Define rotation matrix.
 dTheta = -4*pi / nFrames ;
 R = [cos(dTheta), -sin(dTheta); sin(dTheta), cos(dTheta)] ;

 % - Animate.
 for frameId = 1 : nFrames

    % Update vertices.
    h.Vertices = h.Vertices * R ;

    % Zoom in/out.
    ofs = 6 * ( sin( frameId*dTheta )) ;
    set( gca, 'XLim', [-12+ofs,12-ofs], 'YLim', [-12+ofs,12-ofs] ) ;

    pause( 0.07 ) ;
 end

Answer 2

[David Young]

I'm not quite sure what you want to do, but it feels like cell arrays might be part of the solution. You can store arrays in them and then operate on the arrays:

n = 10;
for ii = 1:n
  H{ii} = randi(9, 1, 4);   % random array
end

disp('Original:')
for ii = 1:n 
  disp(H{ii});
end

for jj = 1:n
  H{jj} = H{jj} + 1;
end

disp('Modified:');
for ii = 1:n 
  disp(H{ii});
end

Note that some authorities feel that i and j are bad choices of loop variable because they are also used for the imaginary unit in MATLAB.

[Nicholas P.]

I've been trying cell arrays to store the shape coordinates, and it does work well, but the problem arises when I want to use set() to update data in the plot instead of replotting the shapes every time I change the coordinates.

Usually if I had something like:

X = [0 1 1 0];
Y = [0 0 1 1];
figure
H = fill(X,Y,'r');

And i wanted to change the coordinates and replot the shape, I would do:

set(H,'YData',Y+1)
set(H,'XData',X+1)
drawnow

Instead of using the fill() command again. Eventually I'm going to be moving dozens of shapes, creating new ones and destroying old ones, which will get very computationally intensive if I am constantly using fill() instead of set() and drawnow.