The slow way:
x = [];
for i = 1:100
y = rand(1, floor(rand*11));
x = [x, y]; % or x = cat(2, x, y)
end
Now the vector x grows in every iteration. Therefore memory for a new vector must be allocated and teh old values are copied.
Filling a vector, cleanup afterwards:
x = nan(100, 10);
for i = 1:100
n = floor(rand*11);
y = rand(1, n);
x(i, 1:n) = y;
end
x(isnan(x)) = []; % Now x is a column vector
Collect the vectors in a cell at first:
C = cell(1, 100);
for i = 1:100
C{i} = rand(1, floor(rand*11));
end
x = cat(2, C{:});
The overhead for creating the CELL is much smaller than the slow method of the growing array.
And if you the array is very large and the section is time-consuming, it matters that cat seems to have problem with a proper pre-allocation internally. Then FEX: Cell2Vec is more efficient.
