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Octave includes support for organizing data in structures. The current implementation uses an associative array with indices limited to strings, but the syntax is more like C-style structures. 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. To print the value of the structure, you can type its name, just as for any other variable:

octave:2> 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.

octave:1> 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.

octave:1> x.b.d = 3 x.b.d = 3 octave:2> x.b ans = { d = 3 } octave: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,

octave:1> a.b.c.d.e = 1; octave:2> a a = { b = { c = { d: 1x1 struct } } }

This prevents long and confusing output from large deeply nested structures.

— Built-in Variable: **struct_levels_to_print**

You can tell Octave how many structure levels to display by setting the built-in variable

`struct_levels_to_print`

. The default value is 2.

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.

octave:1> 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.

octave:2> 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,

octave:1> [ x.u, x.s(2:3,2:3), x.v ] = svd ([1, 2; 3, 4]) x.u = -0.40455 -0.91451 -0.91451 0.40455 x.s = 0.00000 0.00000 0.00000 0.00000 5.46499 0.00000 0.00000 0.00000 0.36597 x.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
(see The for Statement)

The following functions are available to give you information about structures.