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Pig >> mail # user >> FOREACH GENERATE Conditional?

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Hi folks,
I have a pig script that right now looks like this:

likes = FILTER main_set BY blah == 'a' AND meh == 'b';
likes_time = FOREACH likes GENERATE date, 'likes' AS type;

dislikes = FILTER main_set BY blah == 'b' AND meh == 'c';
dislikes_time = FOREACH dislikes GENERATE date, 'dislikes' AS type;

newuserregs = FILTER main_set BY blah == 'c' AND meh == 'd';
newuserregs_time = FOREACH dislikes GENERATE date, 'newuserregs' as type;

all_time = UNION likes_time, dislikes_time, newuserregs_time;

As you can see, what I'm doing is filtering the main_set repeatedly and generating based on that, and then unioning everything back together. This means a lot of extra map jobs, which is a lot of extra work. Really, thinking about it in terms of mapping, I should be able to do things in one run. Any idea what the pig syntax would be for that? Is there something like a GENERATE conditional, where I could do something like:

all_time = FOREACH main_set GENERATE date, 'likes' IF (blah == 'a' AND meh == 'b')
 'dislikes' IF (blah == 'b' AND meh == 'c')
 'dislikes' IF (blah == 'c' AND meh == 'd') AS type;

Running this in just one map job would be very awesome and would speed this script up a ton, I'm thinking. Ideas? Advice?