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Add array_sample() and array_shuffle() functions.

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These are useful in Monte Carlo applications.

Martin Kalcher, reviewed/adjusted by Daniel Gustafsson and myself

Discussion: https://postgr.es/m/9d160a44-7675-51e8-60cf-6d64b76db831@aboutsource.net
This commit is contained in:
Tom Lane
2023-04-07 11:47:07 -04:00
parent cd82e5c79d
commit 888f2ea0a8
6 changed files with 284 additions and 2 deletions
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44
doc/src/sgml/func.sgml
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@ -16053,7 +16053,7 @@ SELECT js,
js IS JSON ARRAY "array?"
FROM (VALUES
('123'), ('"abc"'), ('{"a": "b"}'), ('[1,2]'),('abc')) foo(js);
js | json? | scalar? | object? | array?
js | json? | scalar? | object? | array?
------------+-------+---------+---------+--------
123 | t | t | f | f
"abc" | t | t | f | f
@ -18777,6 +18777,48 @@ SELECT NULLIF(value, '(none)') ...
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_sample</primary>
</indexterm>
<function>array_sample</function> ( <parameter>array</parameter> <type>anyarray</type>, <parameter>n</parameter> <type>integer</type> )
<returnvalue>anyarray</returnvalue>
</para>
<para>
Returns an array of <parameter>n</parameter> items randomly selected
from <parameter>array</parameter>. <parameter>n</parameter> may not
exceed the length of <parameter>array</parameter>'s first dimension.
If <parameter>array</parameter> is multi-dimensional,
an <quote>item</quote> is a slice having a given first subscript.
</para>
<para>
<literal>array_sample(ARRAY[1,2,3,4,5,6], 3)</literal>
<returnvalue>{2,6,1}</returnvalue>
</para>
<para>
<literal>array_sample(ARRAY[[1,2],[3,4],[5,6]], 2)</literal>
<returnvalue>{{5,6},{1,2}}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_shuffle</primary>
</indexterm>
<function>array_shuffle</function> ( <type>anyarray</type> )
<returnvalue>anyarray</returnvalue>
</para>
<para>
Randomly shuffles the first dimension of the array.
</para>
<para>
<literal>array_shuffle(ARRAY[[1,2],[3,4],[5,6]])</literal>
<returnvalue>{{5,6},{1,2},{3,4}}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm id="function-array-to-string">