hadoop - 在 Pig 中将一个元组拆分为多个元组

Question

我喜欢从一个元组生成多个元组。我的意思是: 我有包含以下数据的文件。

>> cat data
ID | ColumnName1:Value1 | ColumnName2:Value2

所以我通过下面的命令加载它

grunt >> A = load '$data' using PigStorage('|');    
grunt >> dump A;    
(ID,ColumnName1:Value1,ColumnName2:Value2) 

现在我想把这个元组拆分成两个元组。

(ID, ColumnName1, Value1)
(ID, ColumnName2, Value2)

我可以将 UDF 与 foreach 一起使用并生成吗？像下面这样的东西？

grunt >> foreach A generate SOMEUDF(A)

编辑:

输入元组:(id1，column1，column2) 输出:两个元组 (id1,column1) 和 (id2,column2) 所以它是 List 还是我应该返回一个 Bag？

public class SPLITTUPPLE extends EvalFunc <List<Tuple>>
{
    public List<Tuple> exec(Tuple input) throws IOException {
        if (input == null || input.size() == 0)
            return null;
        try{
            // not sure how whether I can create tuples on my own. Looks like I should use TupleFactory.
            // return list of tuples.
        }catch(Exception e){
            throw WrappedIOException.wrap("Caught exception processing input row ", e);
        }
    }
}

这种方法是否正确？

Answer 1

您可以编写 UDF 或使用具有内置函数的 PIG 脚本。

例如:

-- data should be chararray, PigStorage('|') return bytearray which will not work for this example
inpt = load '/pig_fun/input/single_tuple_to_multiple.txt' as (line:chararray);

-- split by | and create a row so we can dereference it later
splt = foreach inpt generate FLATTEN(STRSPLIT($0, '\\|')) ;

-- first column is id, rest is converted into a bag and flatten it to make rows
id_vals = foreach splt generate $0 as id, FLATTEN(TOBAG(*)) as value;
-- there will be records with (id, id), but id should not have ':'
id_vals = foreach id_vals generate id, INDEXOF(value, ':') as p, STRSPLIT(value, ':', 2) as vals;
final = foreach (filter id_vals by p != -1) generate id, FLATTEN(vals) as (col, val);
dump final;

测试输入:

1|c1:11:33|c2:12
234|c1:21|c2:22
33|c1:31|c2:32
345|c1:41|c2:42

输出

(1,c1,11:33)
(1,c2,12)
(234,c1,21)
(234,c2,22)
(33,c1,31)
(33,c2,32)
(345,c1,41)
(345,c2,42)

希望对你有帮助。

干杯。