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<title>Creating Structures - GNU Octave</title>
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<a name="Creating-Structures"></a>
<p>
Next: <a rel="next" accesskey="n" href="Manipulating-Structures.html#Manipulating-Structures">Manipulating Structures</a>,
Previous: <a rel="previous" accesskey="p" href="Structure-Arrays.html#Structure-Arrays">Structure Arrays</a>,
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<hr>
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<h4 class="subsection">6.1.3 Creating Structures</h4>
<p><a name="index-dynamic-naming-441"></a>
Besides the index operator ".", Octave can use dynamic naming "(var)" or the
<code>struct</code> function to create structures. Dynamic naming uses the string
value of a variable as the field name. For example:
<pre class="example"> a = "field2";
x.a = 1;
x.(a) = 2;
x
⇒ x =
{
a = 1
field2 = 2
}
</pre>
<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.
<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>
<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:
<pre class="example"> struct ("field1", 1, "field2", 2)
⇒ ans =
{
field1 = 1
field2 = 2
}
</pre>
<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:
<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>
<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:
<pre class="example"> struct ("field1", {{1, "one"}}, "field2", 2)
⇒ ans =
{
field1 =
{
[1,1] = 1
[1,2] = one
}
field2 = 2
}
</pre>
<!-- struct src/ov-struct.cc -->
<p><a name="doc_002dstruct"></a>
<div class="defun">
— Built-in Function: <b>struct</b> (<var>"field", value, "field", value, <small class="dots">...</small></var>)<var><a name="index-struct-442"></a></var><br>
<blockquote>
<p>Create a structure and initialize its value.
<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>If the argument is an object, return the underlying struct.
</p></blockquote></div>
<p>The function <code>isstruct</code> can be used to test if an object is a
structure or a structure array.
<!-- isstruct src/ov-struct.cc -->
<p><a name="doc_002disstruct"></a>
<div class="defun">
— Built-in Function: <b>isstruct</b> (<var>x</var>)<var><a name="index-isstruct-443"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a structure or a structure array.
<!-- Texinfo @sp should work but in practice produces ugly results for HTML. -->
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dismatrix.html#doc_002dismatrix">ismatrix</a>, <a href="doc_002discell.html#doc_002discell">iscell</a>, <a href="doc_002disa.html#doc_002disa">isa</a>.
</p></blockquote></div>
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