How do i define a structure in Matlab

by

You mentioned your goal was to work with several structure of the same type, therefore you should be aware of the main two approaches available to you and how they compare:

1) array of structures

You can initialize it by growing the array dynamically

p(1).str="white";
p(1).r = 1;
p(1).g = 1;
p(1).b = 1;
p(2).str="black";
p(2).r = 0;
p(2).g = 0;
p(2).b = 0;

However its always better to start by pre-allocating the array

p = repmat( struct('r',[], 'g',[], 'b',[], 'str',[]), 1, 10);

another trick to pre-allocate:

p(10) = struct('r',[], 'g',[], 'b',[], 'str',[]);

Or even give all values at initialization:

p = struct('r',{1 0}, 'g',{1 0}, 'b',{1 0}, 'str',{'white' 'black'});

A simple way to fill values

names = {'white' 'black'};
[p(1:2).str] = names{:};
red = num2cell([1 0]);
[p(1:2).r] = red{:};

Here’s how you retrieve all values of one field:

red = [p(:).r];
names = {p(:).str};

2) structures of arrays

p.r = [1 0];
p.g = [1 0];
p.b = [1 0];
p.str = {'white' 'black'};

p1 = [p.r(1) p.g(1) p.b(1)];

The advantage of this is that the structure is simply an array of pointer (r,g,b,str are stored separately in memory). Compare this to the previous approach, where we have an array of structure, and each structure has pointers to its field (there’s quite a memory overhead):

>> s1 = repmat( struct('r',0, 'g',0, 'b',0), 1, 1000);
>> s2 = struct('r',zeros(1,1000), 'g',zeros(1,1000), 'b',zeros(1,1000));
>> whos
  Name      Size               Bytes  Class     Attributes

  s1        1x1000            204192  struct              
  s2        1x1                24372  struct

On the other hand, since each of the fields of a structure is stored as an array of its own, it is up to you to enforce the fact that they have to match in length.

Some others posts if you want to read more about this:

More Related Contents:

  1. maximize the top element of the stack after performing exactly K operations
  2. How do I compare chars (or strings) using void functions, also comparing chars that were taken from a struct array
  3. Generate a matrix containing all combinations of elements taken from n vectors
  4. Linear indexing, logical indexing, and all that
  5. Repeat copies of array elements: Run-length decoding in MATLAB
  6. Element-wise array replication in Matlab
  7. arrayfun can be significantly slower than an explicit loop in matlab. Why?
  8. Using transpose versus ctranspose in MATLAB
  9. How do I do multiple assignment in MATLAB?
  10. MATLAB adding array elements iteratively: time behavior
  11. Array versus linked-list
  12. Matching values in string array
  13. Creating Indicator Matrix
  14. In MATLAB, when is it optimal to use bsxfun?
  15. Array of Matrices in MATLAB
  16. Why do we use arrays instead of other data structures?
  17. Element-wise array replication according to a count [duplicate]
  18. What is the advantage of linspace over the colon “:” operator?
  19. In an assignment A(:) = B, the number of elements in A and B must be the same
  20. How to use cell arrays in Matlab?
  21. how to replicate an array
  22. A data structure supporting O(1) random access and worst-case O(1) append?
  23. Is there anything like deal() for normal MATLAB arrays? [duplicate]
  24. convert string to number array in matlab
  25. How do I iterate through each element in an n-dimensional matrix in MATLAB?
  26. Is indexing vectors in MATLAB inefficient?
  27. How do I remove elements at a set of indices in a vector in MATLAB?
  28. Finding kth smallest number from n sorted arrays
  29. Vector norm of an array of vectors in MATLAB
  30. Is A==0 really better than ~A?

Leave a Comment