hadoop - Pig UDF 计算两个数的幂

Question

我有一个 pig 脚本。

Script.pig:

register /home/cloudera/Desktop/Pow.jar # registering the jar file
A = LOAD '/input.txt' using PigStorage(',') as (a1:int,a2:int,name:chararray); # loading the relation
B = foreach A generate A.a1,A.a2,Pow(A.a1,A.a2); # just generating field1,field2
dump B;# dumping the result

用于计算幂函数的 java UDF。

import java.io.IOException;

import org.apache.pig.EvalFunc;
import org.apache.pig.PigWarning;
import org.apache.pig.data.Tuple;

// Pow function to calculate the power of two numbers    
public class Pow extends EvalFunc<Long> {

public Long exec(Tuple input) throws IOException {
        try {

            int base = (Integer)input.get(0);# Getting the base value from tuple.
            int exponent = (Integer)input.get(1);# Getting the second value from tuple.
            long result = 1;

            /* Probably not the most efficient method...*/
            for (int i = 0; i < exponent; i++) {
                long preresult = result;
                result *= base;
                if (preresult > result) {
                    // We overflowed.  Give a warning, but do not throw an
                    // exception.
                    warn("Overflow!", PigWarning.TOO_LARGE_FOR_INT);
                    // Returning null will indicate to Pig that we failed but
                    // we want to continue execution.
                    return null;
                }
            }
            return result;
        } catch (Exception e) {
            // Throwing an exception will cause the task to fail.
            throw new IOException("Something bad happened!", e);
        }
    }


}

输入文件

Input.txt
1,2,Vijay
3,4,Ram

运行脚本时出现以下错误

 ERROR 1066: Unable to open iterator for alias 

    B. Backend error : Scalar has more than one row in the output. 

    1st : (1,2,Vijay), 2nd :(3,4,Ram)# Error at this point

请帮助我解决这个问题，我也是 Apache pig 的新手。

Answer 1

B = foreach A generate A.a1,A.a2,Pow(A.a1,A.a2);

应该是

B = foreach A generate a1,a2,Pow(a1,a2);