Re: looking for an array-extract-item-as-it operator

(ops, sending to the pgsql-hackers, see the complete thread below)

Adding a formal suggestion after discussion: to include a fast
array_getarray() function!

CREATE FUNCTION array_getarray( m anyarray, idx int ) RETURNS anyarray AS
$f$
-- this is a slow workaround for an (need for) internal operation
WITH item AS (SELECT unnest($1[$2:$2]) as x)
SELECT array_agg(x) FROM item;
$f$ LANGUAGE sql IMMUTABLE;

-- EXAMPLE:
SELECT array_getarray(zz,2) as x, zz[2:2] as y -- x is not same as y!
FROM ( SELECT '{{1,2},{33,44}}'::int[][] as zz ) as tt

2016-01-07 7:26 GMT-02:00 Peter Krauss <ppkrauss(at)gmail(dot)com>:

>
>
> 2016-01-06 20:50 GMT-02:00 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
>
>> Peter Krauss <ppkrauss(at)gmail(dot)com> writes:
>> > I need to access an array-item from an array of arrays.
>>
>> Multi-dimensional arrays in Postgres are *not* "arrays of arrays".
>>
>
> Thanks, you expressed in a little phrase something fundamental to think
> about pg-arrays (!), the pg-Guide need some notices like yours, to remember
> people like me ;-) Well... The good answer closes the question.
>
> - - - -
>
> We can imagine that the "multidimensional array world" is like a data
> type, that is distinct from the "usual array" data type...
> I am starting other discussion...
>
> Let me explain how the question arrives for me: was after working with
> JSONB, where arrays are of "usual array" type.
> Now that PostgreSQL 9.4+ incorporated definitely JSONB, the SQL array data
> type is an important "intermediate" between JSONB and usual SQL structures
> (and type operation algebras).
>
> So, perhaps, PostgreSQL 9.4+ will need a kind of "usual array type", a new
> internal type, and a *cast* function: with this new type will be possible
> to simplify the work with JSONB, and do other things like
> array_agg(array[x,y]).
> ... It is not for final user, perhaps only for developers, or library
> plugins: an "intermediate" type that not broken compatibility... Not very
> useful, a type only to formally express things like to eficient cast, etc.
>
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