使用 PigLatin 删除重复项 [英] Removing duplicates using PigLatin

问题描述

我正在使用 PigLatin 过滤一些记录.

I'm using PigLatin to filter some records.

User1  8 NYC 
User1  9 NYC 
User1  7 LA 
User2  4 NYC
User2  3 DC 

脚本应为用户删除重复项，并保留这些记录之一.类似于 linux 中的唯一命令.

The script should remove the duplicate for users, and keep one of these records. Something like the unique command in linux.

输出应该是:

User1 8 NYC 
User2 4 NYC

有什么建议吗?

推荐答案

对于您的特定示例 distinct 将无法正常工作，因为您的输出包含所有输入列 ($0, $1, $2),您只能在具有 ($0, $2) 或 ($0) 列并丢失 $1 的投影上执行不同的操作.

For your particular example distinct will not work well as your output contains all of the input columns ($0, $1, $2), you can do distinct only on a projection that has columns ($0, $2) or ($0) and lose $1.

为了为每个用户选择一条记录(任何记录)，您可以使用 GROUP BY 和嵌套的 FOREACH 和 LIMIT.例如:

In order to select one record per user (any record) you could use a GROUP BY and a nested FOREACH with LIMIT. Ex:

inpt = load '......' ......;
user_grp = GROUP inpt BY $0;
filtered = FOREACH user_grp {
      top_rec = LIMIT inpt 1;
      GENERATE FLATTEN(top_rec);
};

这种方法将帮助您获得在字段子集上唯一的记录，并限制每个用户的输出记录数，这是您可以控制的.

This approach will help you get records that are unique on a subset of fields and also limit number of output records per each user, which you can control.

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