File Exchange Pick of the Week

April 22nd, 2008

This short video covers the difference between a “structure of arrays” and an “array of structures”.

Video Content

12:28 UTC | Posted in MATLAB Basics, PodCast, Video | Permalink |

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7 Responses to “MATLAB Basics: Array of structures vs Structures of arrays”

1. Emil replied on April 22nd, 2008 at 13:54 UTC :
   

   It’s easier to create vector s by:
   s = [people.SimmNum];

2. Tom replied on April 22nd, 2008 at 16:29 UTC :
   

   This and Emil’s comment were quite helpful to me.

   To take this one step further, one advantage of Arrays of Structures would be the ability to have vectors of different lengths for each numerical part, and a cell array of names of different lengths for each name part.

   For example:

   people(1).name=’Erin’
   people(2).name={’Joan’ ‘Carla’}
   people(1).sim=44
   people(2).sim=[561 49]

3. Doug replied on April 23rd, 2008 at 08:01 UTC :
   

   Emil,

   Yes, you are correct. I can not believe I over looked that. There are so many ways to do certain things in MATLAB.

   Doug

4. Ryan Gray replied on April 24th, 2008 at 14:31 UTC :
   

   If you have an array that you want to assign to a field across a structure array, you can do this:

   [structArray(:).fieldname] = deal(num2cell(array))

   Of course, the length of array should be the same as the length of structArray, but if structArray doesn’t exist yet, then you can do:

   [structArray(1:length(array)).fieldname] = deal(num2cell(array))

   If array is already a cell array, you can avoid using both deal and num2cell (although they will still work) and use:

   [structArray(:).fieldname] = array{:}
   or
   [structArray(1:length(array)).fieldname] = array{:}

   An example, modifying the struct array ‘people’ from the video:

   names = {’Larry’,'Moe’,'Curly’};
   [people(:).name] = names{:};

5. liuzhi replied on May 14th, 2009 at 13:36 UTC :
   

   In one of my program, I’d like to use an array of array of structures, such like

   s0 = struct('field1', [v1 v2], 'field2', [v3 v4]);
   s1 = struct('field1', [v1' v2'], 'field2', [v3' v4']);
   

   I want another data structure s = [s0, s1] so that I can access s0(1) like s(0,1). How can I do that?

6. Doug replied on May 14th, 2009 at 19:19 UTC :
   

   You want to use a cell array here:

   
   s{1} = s0
   s{2} = s1
   s{1}.field1
   s{1}.field1(1,3)
   

   Doug

7. Dan replied on August 4th, 2009 at 19:55 UTC :
   

   I may be wrong, but one of the examples in Post 4 (Ryan Gray) doesn’t work as advertised. Specifically,

   [structArray(1:length(array)).fieldname] = deal(num2cell(array))
   

   ends up assigning the whole array to every instance of fieldname, instead of distributing the array across those instances. What does seem to work is:

   cell_array = num2cell(array);
   [structArray(1:length(array)).fieldname] = cell_array{:};
   

   I leave it as an exercise for a MATLAB guru to splain why this is the case.

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<pre class="code">
a = magic(3);
sum(a)
</pre>

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