800MB is not really big. Such arrays match in the RAM of modern computers easily.
Loading data directly into the workspace by load without catching the outputs, slows down Matlab, because this impedes the JIT acceleration. Try this:
function test
Data = load('landorocean_250_W.mat')
tA_world = Data.A_world;
tx_world = Data.x_world;
ty_world = Data.y_world;
[m_1,n_1]=size(A_world);
island_250m_1 = zeros(m_1, n_1); % Pre-allocation!!!
for i=1:m_1
for j=1:n_1
if tA_world(i,j) == -32768
island_250m_1(i,j)=0;
else
island_250m_1(i,j)=1;
end
end
end
% Or easier without a loop:
% island_250m_1 = (tA_world ~= -32768);
Do not let arrays grow iteratively, because this is extremely expensive. Pre-allocate the create output arrays instead.
