hadoop - PIG Latin 中 FLATTEN 运算符的用途是什么

Question

A = 将“数据”加载为 (x, y)；

B = 将“数据”加载为 (x, z)；

C = cogroup A by x, B by x;

D = foreach C 生成 flatten(A), flatten(b);

E = A::x 组 D

在上面的语句中到底做了什么以及我们在实时场景中使用了展平的地方。

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)