Details
Major Description
Posted this to the pig-users list, and another user indicated he had seen it too, so I thought I'd open a ticket. Adding as major because I can't workaround the projection issue even with numbered $n column names.
I have a log file with events on pages, and the id of the event can be a users login or a users numeric id:
2010-05-14,james
2010-05-15,123
2010-05-15,23
2010-05-15,456
2010-05-15,notjames
So i want to join a set of users on either the login or user id.
Here's my users:
123,james,11
234,notjames,11
456,someoneelse,11
So I thought I would be clever and load the user list, union it with itself to generate a relation where each user is represented twice, once by login, once by id:
logins = FOREACH users GENERATE LOWER(login) as matching_id, user_id as actual_user_id;
user_ids = FOREACH users GENERATE user_id as matching_id, user_id as actual_user_id;
user_id_or_login_lookup = UNION logins, user_ids;
user_id_or_login_lookup:
{matching_id: chararray,actual_user_id: chararray}(123,123)
(234,234)
(456,456)
(james,123)
(notjames,234)
(someoneelse,456)
Then join on that, by the first column, and project that away, leaving just the event info and the numeric id.
views_with_id = JOIN profile_views by viewed_user_id, user_id_or_login_lookup by matching_id;
That is not working however. My joined relation looks like this (which is what I expect)
views_with_id:
{profile_views::date: chararray,profile_views::viewed_user_id: chararray,user_id_or_login_lookup::matching_id: chararray,user_id_or_login_lookup::actual_user_id: chararray}(2010-05-15,123,123,123)
(2010-05-15,456,456,456)
(2010-05-14,james,james,123)
(2010-05-15,notjames,notjames,234)
But when I project as follows: views_with_id_projected = FOREACH views_with_id GENERATE date, viewed_user_id, user_id_or_login_lookup::actual_user_id;
The result is not what I expect
(2010-05-15,123,123)
(2010-05-15,456,456)
(2010-05-14,james,james)
(2010-05-15,notjames,notjames)
To be clear, I expect
(2010-05-15,123,123)
(2010-05-15,456,456)
(2010-05-14,james,123)
(2010-05-15,notjames,456)
Here's my full pig script:
users = LOAD 'patients-test.txt' USING PigStorage(',') AS (user_id:chararray, login:chararray, disease_id: chararray);
profile_views = LOAD 'patient-views-test.txt' USING PigStorage(',') AS(date: chararray, viewed_user_id:chararray);
dump users;
dump profile_views;
– build a relation so that users are present to join by login or user_id
logins = FOREACH users GENERATE LOWER(login) as matching_id, user_id as actual_user_id;
user_ids = FOREACH users GENERATE user_id as matching_id, user_id as actual_user_id;
user_id_or_login_lookup = UNION logins, user_ids;
dump user_id_or_login_lookup;
describe user_id_or_login_lookup;
views_with_id = JOIN profile_views by viewed_user_id, user_id_or_login_lookup by matching_id;
describe views_with_id;
--STORE views_with_id into 'ep-views.txt';
dump views_with_id;
views_with_id_projected = FOREACH views_with_id GENERATE date, viewed_user_id, user_id_or_login_lookup::actual_user_id;
dump views_with_id_projected;