(octave.info)Structure Arrays

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6.1.2 Structure Arrays
----------------------

A structure array is a particular instance of a structure, where each of
the fields of the structure is represented by a cell array.  Each of
these cell arrays has the same dimensions.  Conceptually, a structure
array can also be seen as an array of structures with identical fields.
An example of the creation of a structure array is

     x(1).a = "string1";
     x(2).a = "string2";
     x(1).b = 1;
     x(2).b = 2;

which creates a 1-by-2 structure array with two fields.  Another way to
create a structure array is with the ‘struct’ function (Note: Creating
Structures).  As previously, to print the value of the structure
array, you can type its name:

     x
          ⇒ x =
             {
               1x2 struct array containing the fields:

                 a
                 b
             }

   Individual elements of the structure array can be returned by
indexing the variable like ‘X(1)’, which returns a structure with two
fields:

     x(1)
          ⇒ ans =
             {
               a = string1
               b =  1
             }

   Furthermore, the structure array can return a comma separated list of
field values (Note: Comma Separated Lists), if indexed by one of its
own field names.  For example:

     x.a
          ⇒
             ans = string1
             ans = string2

   Here is another example, using this comma separated list on the
left-hand side of an assignment:

     [x.a] = deal ("new string1", "new string2");
      x(1).a
          ⇒ ans = new string1
      x(2).a
          ⇒ ans = new string2

   Just as for numerical arrays, it is possible to use vectors as
indices (Note: Index Expressions):

     x(3:4) = x(1:2);
     [x([1,3]).a] = deal ("other string1", "other string2");
     x.a
          ⇒
             ans = other string1
             ans = new string2
             ans = other string2
             ans = new string2

   The function ‘size’ will return the size of the structure.  For the
example above

     size (x)
          ⇒ ans =

               1   4

   Elements can be deleted from a structure array in a similar manner to
a numerical array, by assigning the elements to an empty matrix.  For
example

     in = struct ("call1", {x, Inf, "last"},
                  "call2", {x, Inf, "first"})
          ⇒ in =
             {
               1x3 struct array containing the fields:

                 call1
                 call2
             }

     in(1) = [];
     in.call1
          ⇒
            ans = Inf
            ans = last