F.18. intarray
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## F.18. intarray

The `intarray` module provides a number of useful functions and operators for manipulating null-free arrays of integers. There is also support for indexed searches using some of the operators.

All of these operations will throw an error if a supplied array contains any NULL elements.

Many of these operations are only sensible for one-dimensional arrays. Although they will accept input arrays of more dimensions, the data is treated as though it were a linear array in storage order.

This module is considered “trusted”, that is, it can be installed by non-superusers who have `CREATE` privilege on the current database.

### F.18.1. `intarray` Functions and Operators

The functions provided by the `intarray` module are shown in Table F.9, the operators in Table F.10.

Table F.9. `intarray` Functions

Function Description Example(s)
`icount` ( `integer[]` ) → `integer` Returns the number of elements in the array. `icount('{1,2,3}'::integer[])` → `3`
`sort` ( `integer[]`, `dir` `text` ) → `integer[]` Sorts the array in either ascending or descending order. `dir` must be `asc` or `desc`. `sort('{1,3,2}'::integer[], 'desc')` → `{3,2,1}`
`sort` ( `integer[]` ) → `integer[]` `sort_asc` ( `integer[]` ) → `integer[]` Sorts in ascending order. `sort(array[11,77,44])` → `{11,44,77}`
`sort_desc` ( `integer[]` ) → `integer[]` Sorts in descending order. `sort_desc(array[11,77,44])` → `{77,44,11}`
`uniq` ( `integer[]` ) → `integer[]` Removes adjacent duplicates. `uniq(sort('{1,2,3,2,1}'::integer[]))` → `{1,2,3}`
`idx` ( `integer[]`, `item` `integer` ) → `integer` Returns index of the first array element matching `item`, or 0 if no match. `idx(array[11,22,33,22,11], 22)` → `2`
`subarray` ( `integer[]`, `start` `integer`, `len` `integer` ) → `integer[]` Extracts the portion of the array starting at position `start`, with `len` elements. `subarray('{1,2,3,2,1}'::integer[], 2, 3)` → `{2,3,2}`
`subarray` ( `integer[]`, `start` `integer` ) → `integer[]` Extracts the portion of the array starting at position `start`. `subarray('{1,2,3,2,1}'::integer[], 2)` → `{2,3,2,1}`
`intset` ( `integer` ) → `integer[]` Makes a single-element array. `intset(42)` → `{42}`

Table F.10. `intarray` Operators

Operator Description
`integer[]` `&&` `integer[]` → `boolean` Do arrays overlap (have at least one element in common)?
`integer[]` `@>` `integer[]` → `boolean` Does left array contain right array?
`integer[]` `<@` `integer[]` → `boolean` Is left array contained in right array?
`` `#` `integer[]` → `integer` Returns the number of elements in the array.
`integer[]` `#` `integer` → `integer` Returns index of the first array element matching the right argument, or 0 if no match. (Same as `idx` function.)
`integer[]` `+` `integer` → `integer[]` Adds element to end of array.
`integer[]` `+` `integer[]` → `integer[]` Concatenates the arrays.
`integer[]` `-` `integer` → `integer[]` Removes entries matching the right argument from the array.
`integer[]` `-` `integer[]` → `integer[]` Removes elements of the right array from the left array.
`integer[]` `|` `integer` → `integer[]` Computes the union of the arguments.
`integer[]` `|` `integer[]` → `integer[]` Computes the union of the arguments.
`integer[]` `&` `integer[]` → `integer[]` Computes the intersection of the arguments.
`integer[]` `@@` `query_int` → `boolean` Does array satisfy query? (see below)
`query_int` `~~` `integer[]` → `boolean` Does array satisfy query? (commutator of `@@`)

(Before PostgreSQL 8.2, the containment operators `@>` and `<@` were respectively called `@` and `~`. These names are still available, but are deprecated and will eventually be retired. Notice that the old names are reversed from the convention formerly followed by the core geometric data types!)

The operators `&&`, `@>` and `<@` are equivalent to PostgreSQL's built-in operators of the same names, except that they work only on integer arrays that do not contain nulls, while the built-in operators work for any array type. This restriction makes them faster than the built-in operators in many cases.

The `@@` and `~~` operators test whether an array satisfies a query, which is expressed as a value of a specialized data type `query_int`. A query consists of integer values that are checked against the elements of the array, possibly combined using the operators `&` (AND), `|` (OR), and `!` (NOT). Parentheses can be used as needed. For example, the query `1&(2|3)` matches arrays that contain 1 and also contain either 2 or 3.

### F.18.2. Index Support

`intarray` provides index support for the `&&`, `@>`, `<@`, and `@@` operators, as well as regular array equality.

Two parameterized GiST index operator classes are provided: `gist__int_ops` (used by default) is suitable for small- to medium-size data sets, while `gist__intbig_ops` uses a larger signature and is more suitable for indexing large data sets (i.e., columns containing a large number of distinct array values). The implementation uses an RD-tree data structure with built-in lossy compression.

`gist__int_ops` approximates an integer set as an array of integer ranges. Its optional integer parameter `numranges` determines the maximum number of ranges in one index key. The default value of `numranges` is 100. Valid values are between 1 and 253. Using larger arrays as GiST index keys leads to a more precise search (scanning a smaller fraction of the index and fewer heap pages), at the cost of a larger index.

`gist__intbig_ops` approximates an integer set as a bitmap signature. Its optional integer parameter `siglen` determines the signature length in bytes. The default signature length is 16 bytes. Valid values of signature length are between 1 and 2024 bytes. Longer signatures lead to a more precise search (scanning a smaller fraction of the index and fewer heap pages), at the cost of a larger index.

There is also a non-default GIN operator class `gin__int_ops` supporting the same operators.

The choice between GiST and GIN indexing depends on the relative performance characteristics of GiST and GIN, which are discussed elsewhere.

### F.18.3. Example

    -- a message can be in one or more “sections”
    CREATE TABLE message (mid INT PRIMARY KEY, sections INT[], ...);

    -- create specialized index with signature length of 32 bytes
    CREATE INDEX message_rdtree_idx ON message USING GIST (sections gist__intbig_ops (siglen = 32));

    -- select messages in section 1 OR 2 - OVERLAP operator
    SELECT message.mid FROM message WHERE message.sections && '{1,2}';

    -- select messages in sections 1 AND 2 - CONTAINS operator
    SELECT message.mid FROM message WHERE message.sections @> '{1,2}';

    -- the same, using QUERY operator
    SELECT message.mid FROM message WHERE message.sections @@ '1&2'::query_int;

### F.18.4. Benchmark

The source directory `contrib/intarray/bench` contains a benchmark test suite, which can be run against an installed PostgreSQL server. (It also requires `DBD::Pg` to be installed.) To run:

    cd .../contrib/intarray/bench
    createdb TEST
    psql -c "CREATE EXTENSION intarray" TEST
    ./create_test.pl | psql TEST
    ./bench.pl

The `bench.pl` script has numerous options, which are displayed when it is run without any arguments.

### F.18.5. Authors

All work was done by Teodor Sigaev (`<teodor@sigaev.ru>`) and Oleg Bartunov (`<oleg@sai.msu.su>`). See http://www.sai.msu.su/~megera/postgres/gist/ for additional information. Andrey Oktyabrski did a great work on adding new functions and operations.

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