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Re: Problem with memory usage (R2009a)
Posted:
Oct 21, 2009 10:20 AM


"Outspan" <borghiborghi@gmail.com> wrote in message news:720c9267219b4960b3cf305240212df8@o36g2000vbl.googlegroups.com... > On Oct 21, 1:10 pm, "Bruno Luong" <b.lu...@fogale.findmycountry> wrote: > > Outspan <borghibor...@gmail.com> wrote in message > > <3685c1d5be814845bcf290ad72037...@p20g2000vbl.googlegroups.com>... > > > > > even though every single field of the struct is only 8 bytes in size. > > > I hope that in its internal representation it's not replicating the > > > field names 500K times... > > > > No, the internal fieldnames is not duplicated, other internal "things" > > (matlab mxArray like) do. > > > > Drop using array of struct if you want to save memory and speed. > > > > Bruno > > So I should use a matrix instead? Obviously that's going to save > space, but the code is going to get ugly if I ever have to load > different kinds of data for the same record. I just don't understand > why structs have to take up that much space.
Rather than using an array of structs (and incurring the struct header overhead for each element of that array) you could use a struct containing arrays (and incur the header overhead once.)
arrayOfStructs = repmat(struct('x', 1), 1, 1000); for k = 1:1000 arrayOfStructs(k).x = k; end structOfArrays = struct('x', 1:1000); whos arrayOfStructs structOfArrays
Now note there's a tradeoff here  if each element of the arrayOfStructs array contains data about a patient in a doctor's office, for example, then it will be easier to retrieve data about an individual patient by using arrayOfStructs(patientNumber). In structOfArrays, you will need to index into each field (possibly using STRUCTFUN) to retrieve a patient's complete record. On the other hand, if x contains the height of each patient, it's easy to extract that data from structOfArrays (using heights = structOfArrays.x;) but slightly more difficult for arrayOfStructs (you need to remember to use square brackets, as in heights = [arrayOfStructs.x];)
This article from Loren's blog talks a little bit about the differences between an array of structs and a struct containing arrays.
http://blogs.mathworks.com/loren/2006/05/10/memorymanagementforfunctionsandvariables/
as well as this section of the documentation:
http://www.mathworks.com/access/helpdesk/help/techdoc/matlab_prog/brh72ex2.html#brh72ex5
 Steve Lord slord@mathworks.com comp.softsys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ



