BigQuery UDF remove from array. How do I anonymously reference an element in a struct? - struct

Question

This removes the elements from the array, but it renames the field to v.
Is there a better way to do this?
OR
Can I get the first element of the struct (ex. t[0])?
CREATE TEMP FUNCTION remove(arr ANY TYPE, val ANY TYPE) AS ((
SELECT ARRAY_AGG(t)
FROM (SELECT * FROM UNNEST(arr) v) t
WHERE t.v <> val
));

Answer 1

Is there a better way to do this?
Use below trimmed down version
CREATE TEMP FUNCTION remove(arr ANY TYPE, val ANY TYPE) AS ((
SELECT ARRAY_AGG(v)
FROM UNNEST(arr) v
WHERE v <> val
));

Answer 2

Removing any element (val) from an array (arr) is possible, as you showed. Putting the t.v inside the SELECT_ARRAY_AGG let the output be as expected.
CREATE TEMP FUNCTION remove(arr ANY TYPE, val ANY TYPE) AS ((
SELECT ARRAY_AGG(t.v)
FROM (SELECT * FROM UNNEST(arr) v) t
WHERE t.v <> val
));
select remove([1,2,3,4,5],3) as array_without_3

Answer 3

Extracting the first element of a struct is possible. However this is an ugly workaround to do so:
CREATE TEMP FUNCTION firstelement(arr string)
returns string
LANGUAGE js as
"""
var tmp=JSON.parse(arr);
var var1=arr.substring(2,arr.search(':',)-1);
if(!var1.includes('{')) {
return tmp[var1];
}
""";
Select firstelement(TO_JSON_STRING(A)) as A, cast(firstelement(TO_JSON_STRING(B)) as int64) as B,
from (
select struct( "4a" as z,2 as b , 9 as bb) as A, struct( 4 as z,2 as b , 9 as bb) as B
);
At first the struct has to be converted to a JSON string. The function finds the name of the first entry and holds that information in var1. The string is converted toa JSON and the element with the name var1 is read out and returned by the function as a string. If it was a number, in the select statement a cast as is needed.