<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ --> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>Creating Structures (GNU Octave (version 5.1.0))</title> <meta name="description" content="Creating Structures (GNU Octave (version 5.1.0))"> <meta name="keywords" content="Creating Structures (GNU Octave (version 5.1.0))"> <meta name="resource-type" content="document"> <meta name="distribution" content="global"> <meta name="Generator" content="makeinfo"> <link href="index.html#Top" rel="start" title="Top"> <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> <link href="Structures.html#Structures" rel="up" title="Structures"> <link href="Manipulating-Structures.html#Manipulating-Structures" rel="next" title="Manipulating Structures"> <link href="Structure-Arrays.html#Structure-Arrays" rel="prev" title="Structure Arrays"> <style type="text/css"> <!-- a.summary-letter {text-decoration: none} blockquote.indentedblock {margin-right: 0em} blockquote.smallindentedblock {margin-right: 0em; font-size: smaller} blockquote.smallquotation {font-size: smaller} div.display {margin-left: 3.2em} div.example {margin-left: 3.2em} div.lisp {margin-left: 3.2em} div.smalldisplay {margin-left: 3.2em} div.smallexample {margin-left: 3.2em} div.smalllisp {margin-left: 3.2em} kbd {font-style: oblique} pre.display {font-family: inherit} pre.format {font-family: inherit} pre.menu-comment {font-family: serif} pre.menu-preformatted {font-family: serif} pre.smalldisplay {font-family: inherit; font-size: smaller} pre.smallexample {font-size: smaller} pre.smallformat {font-family: inherit; font-size: smaller} pre.smalllisp {font-size: smaller} span.nolinebreak {white-space: nowrap} span.roman {font-family: initial; font-weight: normal} span.sansserif {font-family: sans-serif; font-weight: normal} ul.no-bullet {list-style: none} --> </style> <link rel="stylesheet" type="text/css" href="octave.css"> </head> <body lang="en"> <a name="Creating-Structures"></a> <div class="header"> <p> Next: <a href="Manipulating-Structures.html#Manipulating-Structures" accesskey="n" rel="next">Manipulating Structures</a>, Previous: <a href="Structure-Arrays.html#Structure-Arrays" accesskey="p" rel="prev">Structure Arrays</a>, Up: <a href="Structures.html#Structures" accesskey="u" rel="up">Structures</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> </div> <hr> <a name="Creating-Structures-1"></a> <h4 class="subsection">6.1.3 Creating Structures</h4> <a name="index-dynamic-naming"></a> <p>Besides the index operator <code>"."</code>, Octave can use dynamic naming <code>"(var)"</code> or the <code>struct</code> function to create structures. Dynamic naming uses the string value of a variable as the field name. For example: </p> <div class="example"> <pre class="example">a = "field2"; x.a = 1; x.(a) = 2; x ⇒ x = { a = 1 field2 = 2 } </pre></div> <p>Dynamic indexing also allows you to use arbitrary strings, not merely valid Octave identifiers (note that this does not work on <small>MATLAB</small>): </p> <div class="example"> <pre class="example">a = "long field with spaces (and funny char$)"; x.a = 1; x.(a) = 2; x ⇒ x = { a = 1 long field with spaces (and funny char$) = 2 } </pre></div> <p>The warning id <code>Octave:language-extension</code> can be enabled to warn about this usage. See <a href="Issuing-Warnings.html#XREFwarning_005fids">warning_ids</a>. </p> <p>More realistically, all of the functions that operate on strings can be used to build the correct field name before it is entered into the data structure. </p> <div class="example"> <pre class="example">names = ["Bill"; "Mary"; "John"]; ages = [37; 26; 31]; for i = 1:rows (names) database.(names(i,:)) = ages(i); endfor database ⇒ database = { Bill = 37 Mary = 26 John = 31 } </pre></div> <p>The third way to create structures is the <code>struct</code> command. <code>struct</code> takes pairs of arguments, where the first argument in the pair is the fieldname to include in the structure and the second is a scalar or cell array, representing the values to include in the structure or structure array. For example: </p> <div class="example"> <pre class="example">struct ("field1", 1, "field2", 2) ⇒ ans = { field1 = 1 field2 = 2 } </pre></div> <p>If the values passed to <code>struct</code> are a mix of scalar and cell arrays, then the scalar arguments are expanded to create a structure array with a consistent dimension. For example: </p> <div class="example"> <pre class="example">s = struct ("field1", {1, "one"}, "field2", {2, "two"}, "field3", 3); s.field1 ⇒ ans = 1 ans = one s.field2 ⇒ ans = 2 ans = two s.field3 ⇒ ans = 3 ans = 3 </pre></div> <p>If you want to create a struct which contains a cell array as an individual field, you must wrap it in another cell array as shown in the following example: </p> <div class="example"> <pre class="example">struct ("field1", {{1, "one"}}, "field2", 2) ⇒ ans = { field1 = { [1,1] = 1 [1,2] = one } field2 = 2 } </pre></div> <a name="XREFstruct"></a><dl> <dt><a name="index-struct"></a><em><var>s</var> =</em> <strong>struct</strong> <em>()</em></dt> <dt><a name="index-struct-1"></a><em><var>s</var> =</em> <strong>struct</strong> <em>(<var>field1</var>, <var>value1</var>, <var>field2</var>, <var>value2</var>, …)</em></dt> <dt><a name="index-struct-2"></a><em><var>s</var> =</em> <strong>struct</strong> <em>(<var>obj</var>)</em></dt> <dd> <p>Create a scalar or array structure and initialize its values. </p> <p>The <var>field1</var>, <var>field2</var>, … variables are strings specifying the names of the fields and the <var>value1</var>, <var>value2</var>, … variables can be of any type. </p> <p>If the values are cell arrays, create a structure array and initialize its values. The dimensions of each cell array of values must match. Singleton cells and non-cell values are repeated so that they fill the entire array. If the cells are empty, create an empty structure array with the specified field names. </p> <p>If the argument is an object, return the underlying struct. </p> <p>Observe that the syntax is optimized for struct <strong>arrays</strong>. Consider the following examples: </p> <div class="example"> <pre class="example">struct ("foo", 1) ⇒ scalar structure containing the fields: foo = 1 struct ("foo", {}) ⇒ 0x0 struct array containing the fields: foo struct ("foo", { {} }) ⇒ scalar structure containing the fields: foo = {}(0x0) struct ("foo", {1, 2, 3}) ⇒ 1x3 struct array containing the fields: foo </pre></div> <p>The first case is an ordinary scalar struct—one field, one value. The second produces an empty struct array with one field and no values, since being passed an empty cell array of struct array values. When the value is a cell array containing a single entry, this becomes a scalar struct with that single entry as the value of the field. That single entry happens to be an empty cell array. </p> <p>Finally, if the value is a non-scalar cell array, then <code>struct</code> produces a struct <strong>array</strong>. </p> <p><strong>See also:</strong> <a href="Processing-Data-in-Cell-Arrays.html#XREFcell2struct">cell2struct</a>, <a href="Manipulating-Structures.html#XREFfieldnames">fieldnames</a>, <a href="Manipulating-Structures.html#XREFgetfield">getfield</a>, <a href="Manipulating-Structures.html#XREFsetfield">setfield</a>, <a href="Manipulating-Structures.html#XREFrmfield">rmfield</a>, <a href="Manipulating-Structures.html#XREFisfield">isfield</a>, <a href="Manipulating-Structures.html#XREForderfields">orderfields</a>, <a href="#XREFisstruct">isstruct</a>, <a href="Function-Application.html#XREFstructfun">structfun</a>. </p></dd></dl> <p>The function <code>isstruct</code> can be used to test if an object is a structure or a structure array. </p> <a name="XREFisstruct"></a><dl> <dt><a name="index-isstruct"></a><em></em> <strong>isstruct</strong> <em>(<var>x</var>)</em></dt> <dd><p>Return true if <var>x</var> is a structure or a structure array. </p> <p><strong>See also:</strong> <a href="Predicates-for-Numeric-Objects.html#XREFismatrix">ismatrix</a>, <a href="Basic-Usage-of-Cell-Arrays.html#XREFiscell">iscell</a>, <a href="Built_002din-Data-Types.html#XREFisa">isa</a>. </p></dd></dl> <hr> <div class="header"> <p> Next: <a href="Manipulating-Structures.html#Manipulating-Structures" accesskey="n" rel="next">Manipulating Structures</a>, Previous: <a href="Structure-Arrays.html#Structure-Arrays" accesskey="p" rel="prev">Structure Arrays</a>, Up: <a href="Structures.html#Structures" accesskey="u" rel="up">Structures</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> </div> </body> </html>