Question

我是Apache Pig的新手。是否可以用动态柱创建袋子？以下是脚本，例如。

 A = LOAD 'student' USING PigStorage() AS (col1:chararray, col2:chararray, col3:chararray ....... );
 B = FOREACH A GENERATE col1, col3; OR
 B = FOREACH A GENERATE col2, col3, col4;

简而言之，获取列列表并创建包。有可能吗？怎么样？我需要的是获得动态列的方法。所以例如有人定义我的脚本在params ='col1，col2，col4'上运行，然后我的脚本应该能够解析这个字符串并使用它获得所需的列。

Answer 1

A = LOAD 'student' using PigStorage(',');

by this relation A contains all columns which has student file.You can access these columns by using sequence number like $0,$1,$2
$0 --> First column
$1 --> Second column
$2 --> third column and so on

Answer 2

我可以建议在脚本中使用MACRO或PARAMETER变量，这里的MACRO是示例

define dividend_analysis (daily, year, daily_symbol, daily_open, daily_close) 
returns analyzed { 
divs = load '/user/data/NYSE_dividends'as (exchange:chararray,     symbol:chararray, date:chararray, dividends:float); 
divisthisyear = filter divs by date matches '.*$year.*';
dailythisyear = filter $daily by date matches '.*$year.*'; 
jnd = join divisthisyear by symbol, dailythisyear by $daily_symbol;
$analyzed = foreach jnd generate $1 ,$daily_close - $daily_open; };

daily = load '/user/data/NYSE_daily'as (exchange:chararray, symbol:chararray,     date:chararray, open:float, high:float, low:float, close:float, volume:int,     adj_close:float); 
results = dividend_analysis(daily, '2009', 'symbol', 'open', 'close');

阿帕奇猪袋的动态柱

2 个答案: