Using unnest in multiple rows
You can use the query below;

SELECT
  unnest(i),
  count(*)
FROM (
  VALUES 
    ('{a,b,c,a}'::text[]), 
    ('{a,b,a,b}'), 
    ('{b,a,a,b}')
) AS t(i)
GROUP BY 1, i   -- group by column value, you can use any unique field here
ORDER BY i