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 (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