cells related

Hi all

    I have 450 matrices of order 4X2. I am saving them in a cell on the name, say Vn. So size of Vn is 450X1. And size of each cell is 4X2. Now I want to run a loop and pick the elements randomly from Vn. For example I want to pick 1, 2, 3, 4 rows from the cells 1, 2, 31 , 32. I can access these elements in the way:
Vn{1}(1,:), Vn{2}(2,:), Vn{31}(3,:) etc. As I am running a loop and picking the values randomly, this kind of calling the rows may take long time for the code to run task. Is there any fast / best way to do this?

Thanks in advance Sreenu

Answer 1

[Andrei Bobrov]

variant

numcell = randperm(numel(Vn),4);
rows1 = 1:4;
datarnd = arrayfun(@(x,y)Vn{x}(y,:),numcell,rows1,'un',0);
out = cat(1,datarnd{:});

Answer 2

[Richard]

pre-allocate memory first, this may speed it up.

http://www.mathworks.co.uk/help/techdoc/matlab_prog/f8-784135.html

[KSSV]

Yes it is pre allocated. But thing is some times I may pick two rows from two matrices, or o row from one matrix etc,..it is random...