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<?xml version="1.0" encoding="ISO-8859-1"?>
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-->
<refentry id="fn_gvector_digit_sort">
<refmeta>
<refentrytitle>gvector_digit_sort</refentrytitle>
<refmiscinfo>array</refmiscinfo>
</refmeta>
<refnamediv>
<refname>gvector_digit_sort</refname>
<refpurpose>Performs a stable "digit" sort of a given array.</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis id="fsyn_gvector_digit_sort">
<funcprototype id="fproto_gvector_digit_sort">
<funcdef><function>gvector_digit_sort</function></funcdef>
<paramdef>inout <parameter>data</parameter> vector</paramdef>
<paramdef>in <parameter>elements_in_group</parameter> integer</paramdef>
<paramdef>in <parameter>key_idx_in_group</parameter> integer</paramdef>
<paramdef>in <parameter>sort_ascending</parameter> integer</paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 id="desc_gvector_digit_sort">
<title>Description</title>
<para>The function gets an vector that consists of groups of elements.
All groups are of equal size, namely <parameter>elements_in_group</parameter>, so the total length of <parameter>data</parameter> vector
should be whole multiple of <parameter>elements_in_group</parameter>.
One element of each group is a key of sorting; it is identified by its zero-based position within the group, <parameter>key_idx_in_group</parameter>.
The sorting procedure edits <parameter>data</parameter> and reorders groups in such a way that their keys become ordered ascending or descending,
depending on <parameter>sort_ascending</parameter> flag.</para>
<para>The simplest case is plain sorting of a uniform array. In this case every element is an individual group, <parameter>elements_in_group</parameter> is 1
and <parameter>key_idx_in_group</parameter> is 0.</para>
<para>Other popular case is sorting of result of <link linkend="fn_dict_to_vector"><function>dict_to_vector</function></link>().
In this case, every item of the original dictionary is represended in the vector by a pair of elements (<parameter>elements_in_group</parameter> is 2),
so to sort items by their keys, the <parameter>key_idx_in_group</parameter> is 0 and to sort them by associated values,
the <parameter>key_idx_in_group</parameter> is 1.</para>
<para>The performed sorting is stable. It means that it will not permutate groups in vain: it will preserve the relative order of any two groups that have equal keys.
Using this property, one may sort groups by a "secondary" key and then by "primary" key.
E.g., if each group contain elements for country code and province code then it is possible to make two-field sorting by sorting first by province and then by country;
that will work even if province codes are not globally unique (say, if they're enumerated from 1 in each country).</para>
<para>This function supports only integer values of sorting keys. To sort by strings, floating-point numbers etc., use
<link linkend="fn_gvector_sort"><function>gvector_sort</function></link>().
However, out of these two similar functions, only gvector_digit_sort() is stable-sort.</para>
</refsect1>
<refsect1 id="params_gvector_digit_sort">
<title>Parameters</title>
<refsect2><title>data</title>
<para>A group vector (gvector) to sort.</para>
</refsect2>
<refsect2><title>elements_in_group</title>
<para>The number of vector elements in every group, usually 1, should be in range 1 to 1024.</para>
</refsect2>
<refsect2><title>key_idx_in_group</title>
<para>Zero-based position of key element in group, should be nonnegative and less than <parameter>elements_in_group</parameter>.</para>
</refsect2>
<refsect2><title>sort_ascending</title>
<para>Direction of sorting, nonzero for ascending sort, zero for descending.</para>
</refsect2>
</refsect1>
<refsect1 id="ret_gvector_digit_sort"><title>Return Types</title>
<para>The function returns number of groups in the <parameter>data</parameter> vector</para>.
</refsect1>
<!--
<refsect1 id="errors_gvector_digit_sort">
<title>Errors</title>
<para>This function can generate the following errors:</para>
<errorcode></errorcode>
</refsect1>
<refsect1 id="examples_gvector_digit_sort">
<title>Examples</title>
<example id="ex_gvector_digit_sort"><title></title>
<para></para>
<screen><![CDATA[
]]>
</screen>
</example>
</refsect1> -->
<refsect1 id="seealso_gvector_digit_sort">
<title>See Also</title>
<para><link linkend="fn_gvector_sort"><function>gvector_sort()</function></link></para>
<para><link linkend="fn_rowvector_digit_sort"><function>rowvector_digit_sort()</function></link></para>
<!-- <para><link linkend="fn_rowvector_sort"><function>rowvector_sort</function></link></para> -->
</refsect1>
</refentry>
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