Presto: How to map arrays of different length?

Say I have arrays ['1', '2', '3'] and ['a', 'b', 'c', 'd'] and I want to map them

select map(array ['1', '2', '3'], array ['a', 'b', 'c', 'd'])

This will return an error saying that the arrays need to be of the same length.

How can I replicate the python's zip() which drops the ones without a pair? Or if not, pad the missing ones with NULLs?

You can use slice and cardinality to "fix" sizes:

WITH dataset AS (
  SELECT * 
  FROM 
    (
      VALUES 
        (ARRAY [1, 2, 3], ARRAY[1, 2, 3, 4])
    ) AS t (arr1, arr2)
) 

SELECT 
  map (
    slice(arr1, 1, m), 
    slice(arr2, 1, m)
  ) 
FROM 
  (
    SELECT *, LEAST(cardinality(arr1), cardinality(arr2)) as m 
    FROM 
      dataset
  )

Output:

Or just use zip and transform the resuting array of ROW's into map (note, this relies on default naming convention for elements of ROW, as @Martin Traverso points out in comments in Trino you can access row fields by index, so you can change corresponding line to r -> r[1] IS NOT NULL):

WITH dataset AS (
    SELECT * FROM (VALUES   
       (ARRAY [1,2,3], ARRAY[1,2,3,4])
 ) AS t (arr1, arr2))

SELECT map_from_entries(filter(zip(arr1, arr2), r -> r.field0 is not NULL))
FROM dataset

Output: