Major Description
In our guide, a macro is described for making a three-way left outer join conveniently. We can add this macro to DataFu to make it even easier to use.
The macro's code is as follows:
DEFINE left_outer_join(relation1, key1, relation2, key2, relation3, key3) returns joined {
cogrouped = COGROUP $relation1 BY $key1, $relation2 BY $key2, $relation3 BY $key3;
$joined = FOREACH cogrouped GENERATE
FLATTEN($relation1),
FLATTEN(EmptyBagToNullFields($relation2)),
FLATTEN(EmptyBagToNullFields($relation3));
}
(we would obviously want to add a test for this, too)