Question

Suppose I have a cell array with 3 elements; the first and third cells are matrices, while the second is empty:

>> P
P = 
  [3x8 double]    []    [3x8 double]

I can fill in the second matrix by interpolating for every individual element in the matrix, but surely there must be a way to do this in one shot?

EDIT: An average would certainly work for P. But suppose I have something like

>> Q
Q = [3x8 double]    [3x8 double]     [3x8 double]    []    []    [3x8 double]

So given my four known matrices, I could use a fancier interpolation (like spline) to fill in the missing matrices.

Answer 1

You can perform all the interpolation in a single function call to INTERP1, but it requires setting the data into the desired shape, then back once done:

%# cell array of matrices (some are missing)
sz = [3 8];         %# all of same size
Q = {ones(sz), [], 3*ones(sz), [], [], 6*ones(sz)};

%# indices of missing matrices
idx = ~cellfun(@isempty,Q);
x = 1:numel(Q);

%# merge cells into a multidimensional matrix, call INTERP1, then divide back
QQ = Q(idx);
QQ = permute(cat(3,QQ{:}), [3 1 2]);
QQ = interp1(x(idx), QQ, x);            %# one call to interpolation function
QQ = reshape(num2cell(permute(QQ, [2 3 1]), [1 2]), 1,[]);

Just keep in mind that vectorization sometimes comes at the cost of readability…