I have an array with duplicate values in postgres. For example:
SELECT cardinality(string_to_array('1,2,3,4,4', ',')::int[]) as foo
=> "foo"=>"5"
I would like to get unique elements, for example:
SELECT cardinality(uniq(string_to_array('1,2,3,4,4', ',')::int[])) as foo
=> -- No function matches the given name and argument types. You might need to add explicit type casts.
Can I get unique elements of an array in postgres without using UNNEST ?
I prefer this syntax (about 5% faster)
create or replace function public.array_unique(arr anyarray)
returns anyarray as $body$
select array( select distinct unnest($1) )
$body$ language 'sql';
using:
select array_unique(ARRAY['1','2','3','4','4']);
For integer arrays use intarray extension:
create extension if not exists intarray;
select cardinality(uniq(string_to_array('1,2,3,4,4', ',')::int[])) as foo
or the function
create or replace function public.array_unique(arr anyarray)
returns anyarray
language sql
as $function$
select array_agg(distinct elem)
from unnest(arr) as arr(elem)
$function$;
for any array. You can easily modify the function to preserve the original order of the array elements:
create or replace function public.array_unique_ordered(arr anyarray)
returns anyarray
language sql
as $function$
select array_agg(elem order by ord)
from (
select distinct on(elem) elem, ord
from unnest(arr) with ordinality as arr(elem, ord)
order by elem, ord
) s
$function$;
Example:
with my_data(arr) as (values ('{d,d,a,c,b,b,a,c}'::text[]))
select array_unique(arr), array_unique_ordered(arr)
from my_data
array_unique | array_unique_ordered
--------------+----------------------
{a,b,c,d} | {d,a,c,b}
(1 row)
Going off of @klin's accepted answer, I modified it to remove nulls in the process of choosing only the distinct values.
create or replace function public.array_unique_no_nulls(arr anyarray)
returns anyarray
language sql
as $function$
select array_agg(distinct a)
from (
select unnest(arr) a
) alias
where a is not null
$function$;
uniq(int[])function in theintarraymodule, but other than that, you have to useunnest().