How to write a custom Pig UDF

To write a custom Pig UDF, you need to follow the steps below:

1. Create a Java class that extends org.apache.pig.EvalFunc class.
2. Implement one or more necessary methods, including the exec() method and outputSchema() method.
3. Write custom logic in the exec() method, which takes input data as a parameter and returns the processed result.
4. Define the output schema in the outputSchema() method, describing the type and structure of the output data.
5. Compile and package Java classes into a jar file.
6. Import custom PigUDFs in the Pig script and apply them in the data processing process.

Below is a simple example demonstrating how to write a custom Pig UDF that calculates the length of a string.

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

public class StringLengthUDF extends EvalFunc<Integer> {
    
    @Override
    public Integer exec(Tuple input) throws IOException {
        if (input == null || input.size() == 0) {
            return null;
        }
        
        String str = (String) input.get(0);
        return str.length();
    }
    
    @Override
    public Schema outputSchema(Schema input) {
        return new Schema(new Schema.FieldSchema(null, DataType.INTEGER));
    }
}

Compile and package the above code into a jar file, then import the jar file into a Pig script and use a custom PigUDF for data processing.

REGISTER myudfs.jar;
DEFINE string_length StringLengthUDF();
data = LOAD 'input.txt' AS (str:chararray);
result = FOREACH data GENERATE string_length(str) AS length;

By following the steps above, you can successfully write and use custom Pig UDFs to process data. You can also write more complex UDFs as needed, to achieve more flexible and powerful data processing logic.