Preallocation of a matrix: how to shrink it afterwards?

I'm trying to create an empty epoch for every epoch number in epochn - epochn is a nx1 matrix. How can I preallocate fullstate efficiently? Thanks!

%Create empty epoch for every epoch number
for t = epochn
   idx = find(epochn == t);
   fullstate(t) = state(idx);
   clear idx
end

[Walter Roberson]

Are the entries in epochn unique?

Answer 1

[per isakson]

Something like this

fullstate = class_of_state( size(epochn) );
for t = reshape( epochn, 1,[] )
   idx = find(epochn == t);
   fullstate(t) = state(idx);
   clear idx
end

The variable, state, what type of values does it have?

"shrink it afterwards" why would that be necessary?