这是我的 DESCRIBE A ; DUMP A ; :

A: {first: chararray,second: chararray}
(a,b)
(a,c)
(a,d)
(b,a)
(d,a)
(d,b)

这是解决问题的一种方法：

A = LOAD 'foo.in' AS (first:chararray, second:chararray) ;
-- Can't do a join on its self, so we have to duplicate A
A2 = FOREACH A GENERATE * ;

-- Join the As so that are in (b,a,a,c) etc. pairs.
B = JOIN A BY second, A2 BY first ; 

-- We only want pairs where the first char is equal to the last char.
C = FOREACH (FILTER B BY A::first == A2::second)
    -- Now we project out just one side of the pair.
    GENERATE A::first AS first, A::second AS second ;

输出：

C: {first: chararray,second: chararray}
(b,a)
(d,a)
(a,b)
(a,d)

更新：正如winnienicklaus指出的，这可以缩短为：

B = FOREACH (JOIN A BY (first, second), A2 BY (second, first))
    GENERATE A::first AS first, A::second AS second ;