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Pig UDFs: Extending Pig Functionality with Custom Functions

Extend Apache Pig's capabilities with User-Defined Functions (UDFs). This guide explains how to create custom Pig UDFs in Java and other languages to enhance your data processing logic within Pig scripts.

Pig UDFs (User-Defined Functions)

Introduction to Pig UDFs

Pig, a data flow language for Hadoop, allows you to extend its functionality by creating custom functions called User-Defined Functions (UDFs). UDFs let you incorporate your own logic for data processing, going beyond Pig's built-in functions.

Supported Languages

Pig UDFs can be written in several languages, but Java is most commonly used because it offers the most comprehensive support.

  • Java
  • Python
  • Jython
  • JavaScript
  • Ruby
  • Groovy

Creating a Pig UDF (Java Example)

Let's create a simple Java UDF to convert strings to uppercase. All Pig UDFs extend the `org.apache.pig.EvalFunc` class and must override the `exec()` method:


package com.myudfs; // Replace with your package name

import java.io.IOException;
import org.apache.pig.EvalFunc;
import org.apache.pig.data.Tuple;

public class UppercaseUDF extends EvalFunc<String> {
    @Override
    public String exec(Tuple input) throws IOException {
        if (input == null || input.size() == 0) {
            return null;
        }
        try {
            String str = (String) input.get(0);
            return str.toUpperCase();
        } catch (Exception e) {
            throw new IOException("Error processing input: " + e.getMessage());
        }
    }
}
  1. Compile and Package: Compile this code into a JAR (Java Archive) file. Use your IDE (e.g., Eclipse, IntelliJ) to create the JAR.
  2. Upload the JAR: Upload the JAR file to your Hadoop Distributed File System (HDFS).
  3. Create Input Data: Create a text file (e.g., `input.txt`) with your input data (one string per line).
  4. Upload Input Data: Upload the input file to HDFS.
  5. Write the Pig Script: Write a Pig script (e.g., `script.pig`) to load the data, register your UDF, and apply the UDF:

REGISTER '/path/to/your/uppercase.jar';  --Replace with path to your JAR

A = LOAD '/path/to/your/input.txt' AS (line:chararray); --Replace with path to your input file
B = FOREACH A GENERATE UppercaseUDF(line);
DUMP B;
  1. Run the Script: Execute the Pig script from your terminal.

(The output will be the uppercase versions of the strings in your input file. Example output, assuming your input.txt contains "hello" and "world":)
HELLO
WORLD