How to access the last element in an array ?

Question

In my hive table, the session field is a string in format like:

ip-sessionID-userID or area-sessionID-userID

There's 3 or 4 fields separated by "-", but userID is always the last one.

i wanna select userID, but how to access the last field? In python, there's something like: arr[-1]

but in hive, how to achieve this? The following SQL seems not correct.

select split(session,"\-")[-1] as user from my_table;

Thanks!

Answer 1

reverse(split(reverse(session), '-')[0])

Although this might be a bit more expensive than the regex solution ;)

Answer 2

Because Non-constant expressions for array indexes not supported in hive.

There will be some other ways to solve your problem:

1. use regexp_extract, such as :

   select regexp_extract(session, '(\-[^\-]+)', 1) as user from my_table;

2. use custom hive function : example and document could be found in hive document

Answer 3

One more method without reverse, using array size()-1. This method is more efficient because it does not produce intermediate reversed string, it works only with array.

select array[size(array)-1] as userID
from
( select split(session,'-') array from your_table ) s;

Answer 4

I think the following would be faster than the solution from @arno_v, because it only reverse the view array elements, instead of the whole string, and only reverse once:

reverse(split(session, '-'))[0]