Hadoop Pig Udf Scheme

hadoop pig udf scheme 如果不指定 scheme 当你返回一个tuple里面有大于1个fields的时候， 就必须指定schemea 不然多个field就当作一个field register myudfs.jar; A = load 'student_data' as (name: chararray, age: int, gpa: float); B = foreach A gene

hadoop pig udf scheme

如果不指定 scheme 当你返回一个tuple里面有大于1个fields的时候，

就必须指定schemea 不然多个field就当作一个field

<code>    register myudfs.jar;
    A = load 'student_data' as (name: chararray, age: int, gpa: float);
    B = foreach A generate flatten(myudfs.Swap(name, age)), gpa;
    C = foreach B generate $2;
    D = limit B 20;
    dump D
</code>

This script will result in the following error cause by line 4 ( C = foreach B generate $2;).

<code>java.io.IOException: Out of bound access. Trying to access non-existent column: 2. Schema {bytearray,gpa: float} has 2 column(s).
</code>

This is because Pig is only aware of two columns in B while line 4 is requesting the third column of the tuple. (Column indexing in Pig starts with 0.) The function, including the schema, looks like this:

下面实现了一个schema,输出为4个参数，输出为两个参数，在android上面要用imei和mac去生成一个ukey,在ios平台上，要用 mac和openudid去生成一个ukey

最后返回的是一个platform,ukey

<code>    package kload;
    import java.io.IOException;
    import org.apache.pig.EvalFunc;
    import org.apache.pig.data.Tuple;
    import org.apache.pig.data.TupleFactory;
    import org.apache.pig.impl.logicalLayer.schema.Schema;
    import org.apache.pig.data.DataType;
     /**
      *translate mac,imei,openudid to key
      */
     public class KoudaiFormateUkey extends EvalFunc<tuple>{
         private String ukey = null;
         private String platform = null;
         public Tuple exec(Tuple input) throws IOException {
             if (input == null || input.size() == 0)
                 return null;
             try{
                 String platform = (String)input.get(0);
                 String mac = (String)input.get(1);
                 String imei= (String)input.get(2);
                 String openudID = (String)input.get(3);
                 this.getUkey(platform,mac,imei,openudID);
                 if(this.platform == null || this.ukey == null){
                     return null;
                 }
                 Tuple output = TupleFactory.getInstance().newTuple(2);
                 output.set(0, this.platform);
                 output.set(1, this.ukey);
                 return output;
             }catch(Exception e){
                 throw new IOException("Caught exception processing input row ", e);
             }
         }
         private String getUkey(String platform, String mac, String imei, String openudID){
             String tmpStr = null;
             String ukey = null;
             int pType=-1;
             if(platform == null){
                 return null;
             }
             tmpStr = platform.toUpperCase();
             if(tmpStr.indexOf("IPHONE") != -1){
                 this.platform = "iphone";
                 pType = 1001; 
             }else if(tmpStr.indexOf("ANDROID") != -1){
                 this.platform = "android";
                 pType = 1002; 
             }else if(tmpStr.indexOf("IPAD") != -1){
                 this.platform = "ipad";
                 pType = 1003; 
             }else{
                 this.platform = "unknow";
                 pType = 1004; 
             }
             switch(pType){
                 case 1001:
                     case 1003:
                     if(mac == null && openudID == null){
                         return null;
                     }
                 ukey = String.format("%s_%s",mac,openudID);
                 break;
                 case 1002:
                     if(mac == null && imei== null){
                         return null;
                     }
                 ukey = String.format("%s_%s",mac,imei);
                 break;
                 case 1004:
                     if(mac == null && imei== null && openudID == null){
                         return null;
                     }
                 ukey = String.format("%s_%s_%s",mac,imei,openudID);
                 break;
                 default:
                 break;
             }
             if  (ukey == null || ukey.length() == 0){
                 return null;
             }
             this.ukey = ukey.toUpperCase();
             return this.ukey;
         }
         public Schema outputSchema(Schema input) {
             try{
                 Schema tupleSchema = new Schema();
                 tupleSchema.add(input.getField(0));
                 tupleSchema.add(input.getField(1));
                 return new Schema(new
                         Schema.FieldSchema(getSchemaName(this.getClass().getName().toLowerCase(),
                                 input),tupleSchema, DataType.TUPLE));
             }catch (Exception e){
                 return null;
             }
         }
    }
</tuple></code>

原文地址：Hadoop Pig Udf Scheme, 感谢原作者分享。