What is the fastest way of appending an element to an array?

Question

This is a follow-up question to How to append an element to an array in MATLAB? That question addressed how to append an element to an array. Two approaches are dis

Answer 1

In addition to the fast growing method pointing out above (i.e., A(k+1)), you can also get a speed increase from increasing the array size by some multiple, so that allocations become less as the size increases.

On my laptop using R2014b, a conditional doubling of size results in about a factor of 6 speed increase:

>> SO

GATime =
    0.0288

DWNTime =
    0.0048

In a real application, the size of A would needed to be limited to the needed size or the unfilled results filtered out in some way.

The Code for the SO function is below. I note that I switched to cos(k) since, for some unknown reason, there is a large difference in performance between rand() and rand(1,1) on my machine. But I don't think this affects the outcome too much.

function [] = SO()

    GATime  = timeit(@GrowAlways)
    DWNTime = timeit(@DoubleWhenNeeded)

end


function [] = DoubleWhenNeeded()

    A     = 0;
    sizeA = 1;
    for k = 1:1E5
        if ((k+1) > sizeA)
            A(2*sizeA) = 0;
            sizeA = 2*sizeA;
        end
        A(k+1) = cos(k);
    end

end

function [] = GrowAlways()

    A     = 0;
    for k = 1:1E5
        A(k+1) = cos(k);
    end

end