Info Catalog octave: Structures octave: Structure Arrays

octave: Basic Usage and Examples

 
 6.1.1 Basic Usage and Examples
 ------------------------------
 
 Here are some examples of using data structures in Octave.
 
    Elements of structures can be of any value type.  For example, the
 three expressions
 
      x.a = 1;
      x.b = [1, 2; 3, 4];
      x.c = "string";
 
 create a structure with three elements.  The ‘.’ character separates the
 structure name from the field name and indicates to Octave that this
 variable is a structure.  To print the value of the structure you can
 type its name, just as for any other variable:
 
      x
           ⇒ x =
              {
                a = 1
                b =
 
                  1  2
                  3  4
 
                c = string
              }
 
 Note that Octave may print the elements in any order.
 
    Structures may be copied just like any other variable:
 
      y = x
           ⇒ y =
              {
                a = 1
                b =
 
                  1  2
                  3  4
 
                c = string
              }
 
    Since structures are themselves values, structure elements may
 reference other structures.  The following statements change the value
 of the element ‘b’ of the structure ‘x’ to be a data structure
 containing the single element ‘d’, which has a value of 3.
 
      x.b.d = 3;
      x.b
           ⇒ ans =
              {
                d = 3
              }
 
      x
           ⇒ x =
              {
                a = 1
                b =
                {
                  d = 3
                }
 
                c = string
              }
 
    Note that when Octave prints the value of a structure that contains
 other structures, only a few levels are displayed.  For example:
 
      a.b.c.d.e = 1;
      a
           ⇒ a =
              {
                b =
                {
                  c =
                  {
                    1x1 struct array containing the fields:
 
                    d: 1x1 struct
                  }
                }
              }
 
 This prevents long and confusing output from large deeply nested
 structures.  The number of levels to print for nested structures may be
 set with the function ‘struct_levels_to_print’, and the function
 ‘print_struct_array_contents’ may be used to enable printing of the
 contents of structure arrays.
 
  -- : VAL = struct_levels_to_print ()
  -- : OLD_VAL = struct_levels_to_print (NEW_VAL)
  -- : struct_levels_to_print (NEW_VAL, "local")
      Query or set the internal variable that specifies the number of
      structure levels to display.
 
      When called from inside a function with the "local" option, the
      variable is changed locally for the function and any subroutines it
      calls.  The original variable value is restored when exiting the
      function.
 
      See also: print_struct_array_contents
      XREFprint_struct_array_contents.
 
  -- : VAL = print_struct_array_contents ()
  -- : OLD_VAL = print_struct_array_contents (NEW_VAL)
  -- : print_struct_array_contents (NEW_VAL, "local")
      Query or set the internal variable that specifies whether to print
      struct array contents.
 
      If true, values of struct array elements are printed.  This
      variable does not affect scalar structures whose elements are
      always printed.  In both cases, however, printing will be limited
      to the number of levels specified by STRUCT_LEVELS_TO_PRINT.
 
      When called from inside a function with the "local" option, the
      variable is changed locally for the function and any subroutines it
      calls.  The original variable value is restored when exiting the
      function.
 
      See also: struct_levels_to_print XREFstruct_levels_to_print.
 
    Functions can return structures.  For example, the following function
 separates the real and complex parts of a matrix and stores them in two
 elements of the same structure variable.
 
      function y = f (x)
        y.re = real (x);
        y.im = imag (x);
      endfunction
 
    When called with a complex-valued argument, ‘f’ returns the data
 structure containing the real and imaginary parts of the original
 function argument.
 
      f (rand (2) + rand (2) * I)
           ⇒ ans =
              {
                im =
 
                  0.26475  0.14828
                  0.18436  0.83669
 
                re =
 
                  0.040239  0.242160
                  0.238081  0.402523
 
              }
 
    Function return lists can include structure elements, and they may be
 indexed like any other variable.  For example:
 
      [ x.u, x.s(2:3,2:3), x.v ] = svd ([1, 2; 3, 4]);
      x
           ⇒ x =
              {
                u =
 
                  -0.40455  -0.91451
                  -0.91451   0.40455
 
                s =
 
                   0.00000   0.00000   0.00000
                   0.00000   5.46499   0.00000
                   0.00000   0.00000   0.36597
 
                v =
 
                  -0.57605   0.81742
                  -0.81742  -0.57605
 
              }
 
    It is also possible to cycle through all the elements of a structure
 in a loop, using a special form of the ‘for’ statement (Looping
 Over Structure Elements).
 

Info Catalog octave: Structures octave: Structure Arrays