Comments on: Vectorizing Access to an Array of Structures http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/ Loren Shure works on design of the MATLAB language at MathWorks. She writes here about once a week on MATLAB programming and related topics. Thu, 09 Feb 2012 04:19:21 +0000 hourly 1 http://wordpress.org/?v=3.2.1 By: Loren http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-32598 Loren Mon, 07 Nov 2011 15:49:44 +0000 http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-32598 Liuao- The problem you are encountering is because your right-hand side is not a call that can be dealt out. Try this instead: <pre class="code"> c(3).x = [] [c.y] = c.x d = 1:3 dc = num2cell(d) [c.x] = dc{:} c.x </pre> --Loren Liuao-

The problem you are encountering is because your right-hand side is not a call that can be dealt out. Try this instead:

c(3).x = []
[c.y] = c.x
d = 1:3
dc = num2cell(d)
[c.x] = dc{:}
c.x

–Loren

]]> By: liuao http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-32592 liuao Sat, 05 Nov 2011 12:01:36 +0000 http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-32592 hi,now I have a question about assignment as the following: I have a structure array named c size 3*1,whose fields is x and y,and now I have a array d size 3*1,then I want to assign d to field x of c,how should I do? I have try to type [c.x] = d,[c.x] =deal(d),c.x =d ,c.x=deal(d),but it all doesn't work. Thank you and sorry for my poor english. hi,now I have a question about assignment as the following:
I have a structure array named c size 3*1,whose fields is x and y,and now I have a array d size 3*1,then I want to assign
d to field x of c,how should I do?
I have try to type [c.x] = d,[c.x] =deal(d),c.x =d ,c.x=deal(d),but it all doesn’t work.

Thank you and sorry for my poor english.

]]> By: Loren http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-31493 Loren Sun, 11 Jul 2010 20:13:51 +0000 http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-31493 Vince- That's similar to the way I would solve the problem as well - except I would not look for exact floating point numbers but within a range since there are numeric roundoff considerations to account for when working with floating point. I also would probably use ismember with the rows option after getting the data out of the struct. --Loren Vince-

That’s similar to the way I would solve the problem as well – except I would not look for exact floating point numbers but within a range since there are numeric roundoff considerations to account for when working with floating point. I also would probably use ismember with the rows option after getting the data out of the struct.

–Loren

]]> By: Vince http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-31492 Vince Sun, 11 Jul 2010 11:23:27 +0000 http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-31492 Hi Loren, I'm new in using array of structures. I have an array of structures called "list_uwv". Each structure has a field called "cord", in which I've placed a vector like this [a b c], where a,b,c are three numbers. My question is how can ask to the array of structures where is located the vector [A B C]; there is any function, like "find", can I use for? i.e <pre> find(list_uwv.cord(:) == [0 3.5 0.8])) </pre> Up to now I've placed the vectors in a matrix (array of Nx3 elements) and I make the query to the matrix by using find function. TNX a lot Loren Hi Loren,
I’m new in using array of structures. I have an array of structures called “list_uwv”. Each structure has a field called “cord”, in which I’ve placed a vector like this [a b c], where a,b,c are three numbers. My question is how can ask to the array of structures where is located the vector [A B C]; there is any function, like “find”, can I use for?
i.e 

find(list_uwv.cord(:) == [0 3.5 0.8]))

Up to now I’ve placed the vectors in a matrix (array of Nx3 elements) and I make the query to the matrix by using find function.
TNX a lot Loren

]]> By: Loren http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-30230 Loren Fri, 24 Apr 2009 16:39:13 +0000 http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-30230 Tom- Thanks for the suggestion about the doc. I will pass it on. --Loren Tom-

Thanks for the suggestion about the doc. I will pass it on.

–Loren

]]> By: Tom http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-30228 Tom Fri, 24 Apr 2009 00:17:01 +0000 http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-30228 Sorry, the above is related to WHY THERE ARE SO MANY QUESTIONS IN THIS AREA. Sorry, the above is related to WHY THERE ARE SO MANY QUESTIONS IN THIS AREA.

]]> By: Tom http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-30227 Tom Fri, 24 Apr 2009 00:15:52 +0000 http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-30227 I think the biggest problem is the matlab help tells you how to BUILD a matrix/array/structure/string/cell but does not ON THE SAME PAGE tell you the syntax to get the data in such a type BACK OUT!! Finding out how to get data OUT of these various storage types is not easy to find. I am a new user of matlab, and my biggest problem is getting the words I use in the help search function to relate to the words used as commands in the program... ie "How do I get data out of a structure" does not give me an answer about structures "structure" tells me how to build one, but not how to USE it, or how to get data inside a feild out and into a plot. Cheers, Tomas I think the biggest problem is the matlab help tells you how to BUILD a matrix/array/structure/string/cell but does not ON THE SAME PAGE tell you the syntax to get the data in such a type BACK OUT!! Finding out how to get data OUT of these various storage types is not easy to find.

I am a new user of matlab, and my biggest problem is getting the words I use in the help search function to relate to the words used as commands in the program…

ie “How do I get data out of a structure” does not give me an answer about structures
“structure” tells me how to build one, but not how to USE it, or how to get data inside a feild out and into a plot.

Cheers,
Tomas

]]> By: Loren http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-30090 Loren Thu, 05 Mar 2009 16:28:10 +0000 http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-30090 Jaime- Look at arrayfun. It might well be able to help you out here. --Loren Jaime-

Look at arrayfun. It might well be able to help you out here.

–Loren

]]> By: Jaime X. Ramos http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-30083 Jaime X. Ramos Wed, 04 Mar 2009 17:14:10 +0000 http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-30083 I have the same question as 'F. Moisy' who replied on April 19th, 2007 at 15:01 UTC, except I have set of m x n matrices as field contents of a structure array. I'm gathering that I can only access say the (2,3) element for all structures in the array by iterating with a for loop, ie there's no compact access code like he wrote with [struct.data(2,3)] for i = 1:k struct(i).mat(2,3) end I'm reading a tiff stack file using this matlab community user code and they store the frames as structures in a structure array. I'm trying to compute the mode of a given pixel across all the frames but I can't see no way other than iteratively accessing that pixel. Any ideas? thanks for being such a champ! =) Jaime I have the same question as ‘F. Moisy’ who replied on April 19th, 2007 at 15:01 UTC, except I have set of m x n matrices as field contents of a structure array.

I’m gathering that I can only access say the (2,3) element for all structures in the array by iterating with a for loop, ie there’s no compact access code like he wrote with
[struct.data(2,3)]

for i = 1:k
struct(i).mat(2,3)
end

I’m reading a tiff stack file using this matlab community user code and they store the frames as structures in a structure array. I’m trying to compute the mode of a given pixel across all the frames but I can’t see no way other than iteratively accessing that pixel.

Any ideas?

thanks for being such a champ! =)

Jaime

]]> By: KenA http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-29667 KenA Thu, 07 Aug 2008 16:49:31 +0000 http://blogs.mathworks.com/loren/2007/04/19/vectorizing-access-to-an-array-of-structures/#comment-29667 It may be worth point out that, in R2008a at least, the properties of an array of objects can be indexed as discussed in this blog posting. To Mortiz’s post (27), this also not super-speedy, performing between the example’s “HybridTime” and “StructureTime”. However, according “whos”, an array of classes is far more memory efficient than an equivalent array of structs. So, if you find yourself creating a large array of structs, where those structs all have the same field names (homogeneous), an array of objects may be something to consider. It may be worth point out that, in R2008a at least, the properties of an array of objects can be indexed as discussed in this blog posting. To Mortiz’s post (27), this also not super-speedy, performing between the example’s “HybridTime” and “StructureTime”. However, according “whos”, an array of classes is far more memory efficient than an equivalent array of structs.

So, if you find yourself creating a large array of structs, where those structs all have the same field names (homogeneous), an array of objects may be something to consider.

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