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 2-by-1 structure array with two fields. Another way to create a structure array is with the struct function (see 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 (see 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 (see 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