Comments on: MATLAB Basics: Array of structures vs Structures of arrays

By: Greg Stupp

Greg Stupp — Wed, 12 Dec 2012 20:44:19 +0000

This may be helpful to someone. I couldn’t find a built-in function or anything in the file exchange that does this.

function out=SoA2AoS(in)
%convert structure of arrays to an array of structures
%the lengths of the fields must be the same

% example:
% in.a=[1:5];
% in.b=[11:15];
% out=SoA2AoS(in)
% out(1)

fn=fieldnames(in);
c=struct2cell(in);

for i=1:length(fn)
d=num2cell(c{i});
m=num2str(length(d));
eval(['[out(1:' m ').' fn{i} ']=deal(d{:});’])
end

By: Asit

Asit — Wed, 20 Jun 2012 06:14:54 +0000

Hi.
while populating an array of structures, can I use such a syntax as
data(3:10).pin = [6 7];
I am getting an error while trying to use this. I hope it is clear as to what I want to achieve. Please let me know if there is a work around.

Thanks,
a.

By: Shaheen Iqubal

Shaheen Iqubal — Tue, 08 May 2012 21:21:01 +0000

Hi,
I am trying to merge two array of structure based on the common field security_ID. The last two lines does not seem to work. I want to assign the Return and ReturnDt column from T2 array into T1 array. It is possible that some security_id that are in T1 are not in T2 and vice-versa. I can do the assignment in the loop or use arrayfun but trying to do in one line of code.

ID1=[T1.Security_ID];
ID2=[T2.Security_ID];
[a,b,c]=intersect(ID1,ID2);
T1(b).Return=[T2(c).Return];
T1(b).ReturnDt=[T2(c).ReturnDt];

By: tavi

tavi — Mon, 19 Mar 2012 13:25:30 +0000

For example my parameters should be initialize like this: in the first position of my structure I have a number, in the second position a number, in the third position a vector and so on till the 9th position.

Regards,
Octavian

By: tavi

tavi — Mon, 19 Mar 2012 13:20:24 +0000

I have a question. How do I create a structure in order to initialize some parameters needed in other functions? If someone is interested in answering this question I will write him a part of the code.

Regards,
Octavian

By: F. Ojeda

F. Ojeda — Thu, 23 Feb 2012 16:00:21 +0000

Hi I’ve been looking through your post but couldn’t find and answer to my problem, which resides in the “array of structures”- “structure of arrays” paradigm

I have the following text file containing exchange rates,

id code rate
1 Euro 1
2 HUF 0.0036
3 PZL 0.2532
4 CZK 0.0406
5 SKK 0.03319
6 BGN 0.5113

which I want to import into an “array of structures”, of the form

currency(1).id = 1
currency(1).code = ‘Euro’
currency(1).rate = 1
.
.
.
currency(6).id = 6
currency(6).code = ‘BGN’
currency(6).rate = 0.5113

Of course I’d like to avoid this manual work with for loops and instead create dynamicaly the structure fields using the file headers and populating the structure.

My immediate approach was first to read the file with textscan

fid = fopen(‘file.txt’)
names = textscan(fid,’%s %s %s’,1,’CollectOutput’,1);
values = textscan(fid,’%s %s %s’,'CollectOutput’,1);
fclose(fid)

thus generating two cell arrays. Secondly, I use the cell2struct function as

currency = cell2struct(content,headers{:},2)

which creates a “structure of arrays”

currency =
id: [6x1 uint32]
code: 1×1 cell array
rate: [6x1 double]

The indexing is the of the form

currency.id(1)
currency.code{1}

How could I then generate using the same reasoning an array of structures?

thanks

By: Paul Torek

Paul Torek — Mon, 19 Dec 2011 20:45:24 +0000

Thankyou thankyou thankyou!

You gave me the direction I needed to extract relevant info from the matlab dir filename command. Such as:

function Subdirs = OneLevelSubDirs(directory,match)
% xxx Need Help xxx
% Subdirs = OneLevelSubDirs(directory,match)

if nargin < 2 || isempty(match)
match = '*';
end

X = dir(directory);

Xdir = {X(:).name};
Xdir = Xdir(find(cell2mat({X(:).isdir})));
Subdirs = Xdir(~cellfun(@(x)ismember(x,{'.';'..'}),Xdir));

Did I mention thank you?

By: nick

nick — Thu, 13 Oct 2011 15:43:16 +0000

hi
i am new in MATLAB, can u plz tell whats d problem with the following statements (i need to assign an array of integers to a member of an array of structures )
n(1).loc=[x-1 y+1];
n(2).loc=[x y+1];
n(3).loc=[x+1 y+1];
n(4).loc=[x+1 y];
n(5).loc=[x+1 y-1];
why are these assignments wrong?? plz reply ASAP… thnx

By: Omar

Omar — Tue, 27 Sep 2011 21:36:07 +0000

I want to have a .wav file into a vector so I can create de Spectra with the SPtool.

When I use the wavread() function and import the data into sptool it say thats an [array] so i couldnt create the spectrum, this tool only work with vectors. So how can i turn this array into vector?

a little help here please

By: Steve L

Steve L — Fri, 19 Aug 2011 13:16:45 +0000

Annon, To do this you can use DEAL, but I think Doug's question is a good one: why do you need/want to do it this way?

% Make sure people2 doesn't exist yet
% This way you can tell that the command performed
% the initial creation correctly
clear people2

% Define the cell array of names
S = {'bob', 'john'};

% DEAL the elements of the cell into the struct
[people2(1:2).name] = deal(S{:})

If you're using release R14 or later, you can omit the DEAL as described in the Release Notes.