PostgreSQL array - Remove consecutive identical values [duplicate] - arrays

Question

This question already has answers here:
Remove consecutive duplicate rows in Postgresql
(2 answers)
Closed 1 year ago.
In a PostgreSQL text array I want to remove consecutive identical values. A distinct isn't enough because I can have duplicate values but not consecutive, and I want to keep them. The order of values have importance.
For example
SELECT ARRAY['A', 'B', 'C', 'C', 'D', 'A'];
Should return {A,B,C,D,A}
-- Edit
AS #MkSpring Mk said, this post suggest an answer. I try to adapt it:
WITH q_array AS (
SELECT ARRAY['A', 'B', 'C', 'C', 'D', 'A'] AS full_array
), q_unnest AS (
SELECT
unnest(full_array) AS unnest_array
FROM q_array
), q_id AS (
SELECT
row_number() OVER () AS id,
unnest_array
FROM q_unnest
)
SELECT
array_agg(q_id.unnest_array) AS array_logical
FROM (SELECT q_id.*, lag(q_id.unnest_array) OVER (ORDER BY q_id.id) AS unnest_array_logical FROM q_id) q_id
WHERE unnest_array_logical IS DISTINCT FROM q_id.unnest_array
I find this syntax very verbose, maybe my approach is not efficient enough.
Is this syntax ok ? Is it a best practice to create a function or can I write it directly in a query ?

Answer 1

To improve query performance, I made this function:
CREATE OR REPLACE FUNCTION array_remove_consecutive_duplicates(
array_vals anyarray)
RETURNS TABLE(array_logical anyarray)
LANGUAGE 'plpgsql'
COST 100
VOLATILE PARALLEL UNSAFE
ROWS 1000
AS $BODY$
BEGIN
RETURN QUERY
WITH q_array AS (
SELECT array_vals AS full_array
), q_unnest AS (
SELECT
unnest(full_array) AS unnest_array
FROM q_array
), q_id AS (
SELECT
row_number() OVER () AS id,
unnest_array
FROM q_unnest
)
SELECT
array_agg(q_id.unnest_array) AS array_logical
FROM (SELECT q_id.*, lag(q_id.unnest_array) OVER (ORDER BY q_id.id) AS unnest_array_logical FROM q_id) q_id
WHERE unnest_array_logical IS DISTINCT FROM q_id.unnest_array;
END;
$BODY$;
My query will now write like this:
SELECT array_remove_consecutive_duplicates(ARRAY['A', 'B', 'C', 'C', 'D', 'A']);
It's a bit faster and easier to use in a query than my fist approach. Maybe it's not the good way or my syntax isn't efficient. If someone have a better way to suggest, I'll take it.