你能试试这个吗？
输入：

a, 2
b, 1
a, 5
c, 5
d, 3
a, 3

Pig手稿：

A = LOAD 'input' USING PigStorage(',') AS (col1:chararray,col2:chararray);
B = GROUP A BY col1;
C = FOREACH B {
                 sortedRow = ORDER A BY col2 ASC;
                 GENERATE group,FLATTEN(REPLACE(BagToString(sortedRow.$1.col2),'_\\s+',','));
              }
STORE C INTO 'output' USING PigStorage(',');

输出：（将存储在 output/part* 文件）

a, 2,3,5
b, 1
c, 5
d, 3