FLATTEN操作符在PIG拉丁语中的用途是什么？

Question

A = load'data'as（x，y）; （x，z）; B =加载'数据'为（x，z）;

C = cogroup A by x，B by x; D = foreach C生成flatten（A），flatten（b）;

E =组由A :: d X

究竟在上面的语句完成，在这里我们使用实时场景扁平化。

Answer 1

A = load 'input1' USING PigStorage(',') as (x, y); 
(x,y) --> (1,2)(1,3)(2,3) 
B = load 'input2' USING PigStorage(',') as (x, z);` 
(x,z) --> (1,4)(1,2)(3,2)*/ 
C = cogroup A by x, B by x;` 

result: 

(1,{(1,2),(1,3)},{(1,4),(1,2)}) 
(2,{(2,3)},{}) 
(3,{},{(3,2)}) 


D = foreach C generate group, flatten(A), flatten(B);` 

when both bags flattened, the cross product of tuples are returned. 

result: 
(1,1,2,1,4) 
(1,1,2,1,2) 
(1,1,3,1,4) 
(1,1,3,1,2) 

E = group D by A::x` 

here your are grouping with x column of relation A. 

（1,1,2,1,4） （1,1,2,1,2） （1,1,3,1,4） （1,1,3-， 1,2）