pig trial-group,foreach

A = load '/user/cloudera/lab/mydata' using PigStorage() as (a,b,c);

如果写成 A=load 就会出现  [main] ERROR org.apache.pig.tools.grunt.Grunt - ERROR 1000: Error during parsing. Encountered " "A=load "" at line 1, column 1.

​(1,2,3)

(4,2,1)

(8,3,4)

(4,3,3)

(7,2,5)

(8,4,3)

B = group A by a;​

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

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

(7,{(7,2,5)})

(8,{(8,4,3),(8,3,4)})

​C = foreach B { D = distinct A.b; generate flatten(group), COUNT(D); };

把"("写成中文"（ " 会报错  Unexpected character '.

B的第一个字段有固定的名字，叫group，因为它是由group操作生成的。

​上面语句中D = distinct A.b;       A 指 B的第二个字段，保留生成B的时候 relation的名字，这里是以下值 

(1,2,3)

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

(7,2,5)

(8,4,4), (8,3,4)

所以 D 每次是

2

3，2

2

4，3

>> generate flatten(group), COUNT(D);

(1,1)

(4,2)

(7,1)

(8,2)

=========================

GROUP creates a nested set of output tuples while JOIN creates a flat set of output tuples​

The first field is named "group" (do not confuse this with the GROUP operator) and is the same type as the group key.  ​

The second field takes the name of the original relation and is type bag.

# so "group" is the key name, and "A or B the original alias" is the nested set name​

​