Postgres: Window Function row_number() wrong output? - row

Question

i have a confussing problem here. I'm working with some arrays and trying to get the 10 minors values from all of them merged as well as the array they are within and the position they are inside such array.
My relation is arrays(id int, array float[]);
So, on it i have several stored arrays:
1, '{v1,v2,v3,v4,v5...}'
2, '{v1,v2,v3,v4,v5...}'...etc
My first query is next:
WITH T1 AS(SELECT id, unnest(array) value from arrays order by value LIMIT 10)
SELECT T1.id as id, cell(array,value) as offset, value from T1;
In this case cell() is an UDF i developed to return the position given an array and an arbitrary value.
The second query (using w-functions) is next:
WITH T1 AS(SELECT id, unnest(array) value from arrays)
SELECT id, row_number() over (partition by sid) as offset, value from T1 order by value LIMIT 10;
Despite they both return the same values (which is correct), the offset is not the same and seems they are somehow upside-down.
These are some examples outputs with bigger arrays im working with, and you can see the problemim having.
Query 1 output:
id | offset | value
-----+--------+-----------
1 | 17569 | 0.0156216
1 | 20801 | 0.0164499
1 | 20802 | 0.0171007
1 | 17570 | 0.0171008
1 | 17568 | 0.0180476
1 | 20800 | 0.0182249
1 | 20803 | 0.0194675
1 | 1411 | 0.02142
1 | 1412 | 0.02142
1 | 1413 | 0.0215976
Query 2 output:
id | offset | value
-----+--------+-----------
1 | 6591 | 0.0156216
1 | 9823 | 0.0164499
1 | 9824 | 0.0171007
1 | 6592 | 0.0171008
1 | 6590 | 0.0180476
1 | 9822 | 0.0182249
1 | 9825 | 0.0194675
1 | 26144 | 0.02142
1 | 26140 | 0.02142
1 | 26149 | 0.0215976
I would appreciate any help please. Thank you!

Answer 1

You haven't got an order specified in your window function in Query 2, which means that Postgres will probably be internally sorting by sid - before you outer ORDER BY value is applied.
WITH t1 AS (
SELECT id, UNNEST( array ) AS value
FROM arrays
)
SELECT id, row_number() OVER ( PARTITION BY sid ORDER BY value ) as offset, value
FROM t1
ORDER BY value
LIMIT 10;