你能试试这个吗？
输入文件

1       2
1       3
1       4
2       1
2       5
3       1
4       8

Pig手稿：

A = LOAD  'input.txt' USING PigStorage() AS(id:int,friends:int);
B = GROUP A BY id;
C = FOREACH B GENERATE FLATTEN(COUNT(A.friends)) AS cnt;
D = GROUP C BY cnt;
E = FOREACH D GENERATE COUNT(C.cnt),group;
F = ORDER E BY group DESC;
DUMP F;

输出：

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