k = {StAr.f1};
out = zeros(size(k));
nonempty = ~cellfun(@isempty,k);
out(nonempty) = [StAr.f1]; % (1)
idx = find(nonempty); % (2)
EDIT
k = {StAr.f1};
k1 = cellfun(@(x)x(:).',k,'un',0);
ii = cellfun(@isempty,k1);
k1(ii) = {0};
out = cell2mat(k1); % (1)
idx = find(ii); % (2)
EDIT 2
k = reshape({StAr.f1},size(StAr));
k2 = cellfun(@(x)x(:).',k,'un',0);
ii = cellfun(@isempty,k2);
k2(ii) = {nan};
s2 = cellfun('size',k2,2);
out = cell2mat(cellfun(@(x,y)[x,nan(1,y - numel(x))],...
k2,num2cell(ones(size(s2,1),1)*max(s2)),'un',0));
