FOREACH 运算符用于根据列数据生成指定的数据转换.
给定以下是 FOREACH 运算符的语法.
grunt> Relation_name2 = FOREACH Relatin_name1 GENERATE (required data);
假设我们在HDFS中有一个名为 student_details.txt 的文件目录/pig_data/如下所示.
student_details.txt
001,Rajiv,Reddy,21,9848022337,Hyderabad 002,siddarth,Battacharya,22,9848022338,Kolkata 003,Rajesh,Khanna,22,9848022339,Delhi 004,Preethi,Agarwal,21,9848022330,Pune 005,Trupthi,Mohanthy,23,9848022336,Bhuwaneshwar 006,Archana,Mishra,23,9848022335,Chennai 007,Komal,Nayak,24,9848022334,trivendram 008,Bharathi,Nambiayar,24,9848022333,Chennai
我们已将此文件加载到Pig with关系名称 student_details 如下所示.
grunt> student_details = LOAD 'hdfs://localhost:9000/pig_data/student_details.txt' USING PigStorage(',') as (id:int, firstname:chararray, lastname:chararray,age:int, phone:chararray, city:chararray);
现在让我们从关系 student_details 中获取每个学生的身份,年龄和城市价值,并将其存储到另一个关系中使用 foreach 运算符命名为 foreach_data ,如下所示.
grunt> foreach_data = FOREACH student_details GENERATE id,age,city;
使用 DUMP foreach_data >运算符如下所示.
grunt> Dump foreach_data;
它将产生以下输出,显示关系 foreach_data .
(1,21,Hyderabad) (2,22,Kolkata) (3,22,Delhi) (4,21,Pune) (5,23,Bhuwaneshwar) (6,23,Chennai) (7,24,trivendram) (8,24,Chennai)