Accumulating different sized column vectors stored as a cell array into a matrix padded with NaNs

Question

Imagine I have a series of different sized column vectors inside an array and want to group them into a matrix by padding the empty spaces with NaN. How can I d

Answer 1

If you want speed the cell data structure is your enemy. For this example I will assume you have this vectors stored in a structure called vector_holder:

elements = fieldnames(vector_holder);

% Per Dan request
maximum_size = max(structfun(@max, vector_holder));

% maximum_size is the maximum length of all your separate arrays
matrix = NaN(length(elements), maximum_size);

for i = 1:length(elements)
    current_length = length(vector.holder(element{i}));
    matrix(i, 1:current_length) = vector.holder(element{i});
end

Many Matlab functions are slower when dealing with cell variables. In addition, a cell matrix with N double-precision elements requires more memory than a double-precision matrix with N elements.