问题描述
我试图找到一年内在最多球队中出场的球员。我有一个包含 PlayerID、yearID、teamID 架构的文件。我将文件带入两次以尝试加入 PlayerID 和 yearID 相等但 teamID 不相等的地方。我在 PIG 中怎么做?我可以在 join 语句中使用 吗?我需要将它们分组并进行比较吗?我知道 sql 我可以根据 PlayerID 和 yearID 相等而 teamID 不相等而加入,但不确定如何在 PIG 中执行此操作。
我试过了,但它的语法不正确"
batters = LOAD 'hdfs:/user/maria_dev/pigtest/Batting.csv' USING PigStorage(',') AS
(id:chararray,yearid:int,teamid:chararray);
batters1 = LOAD 'hdfs:/user/maria_dev/pigtest/Batting.csv' USING PigStorage(',') AS ` (id:chararray,teamid:chararray);
batter_fltr = FILTER batters BY (yearid > 0) AND (teamid> ' ');
batter1_fltr = FILTER batters1 BY (yearid>0) AND (teamid> ' ');
multi_playr = JOIN batter_fltr BY (yearid,id),batter1_fltr BY(yearid,LEFT OUTER BY(teamid);
解决方法
您想找到一年内在球队中出场次数最多的球员。因此,您应该按球员和年份分组,然后您可以计算每个球员每年的球队数量。最后,按计数降序对数据进行排序 - 第一个结果将是您的答案。无需两次加载数据或进行连接。
batters = LOAD 'hdfs:/user/maria_dev/pigtest/Batting.csv' USING PigStorage(',') AS
(id:chararray,yearid:int,teamid:chararray);
-- Apply filtering as needed here
teams_per_year = FOREACH (GROUP batters BY (id,yearid))
GENERATE
group.id AS id,group.yearid AS yearid,COUNT(batters.teamid) AS num_teams;
ordered_results = ORDER teams_per_year BY num_teams DESC;
DUMP ordered_results;
如果您需要不同数量的团队,请添加嵌套的 DISTINCT
:
teams_per_year = FOREACH (GROUP batters BY (id,yearid)) {
dist_teams = DISTINCT batters.teamid;
GENERATE
group.id AS id,COUNT(dist_teams) AS num_teams;
}