How to write UDF in Pig

While writing UDF’s using Java, we can create and use the following three types of functions −

• Filter Functions − The filter functions are used as conditions in filter statements. These functions accept a Pig value as input and return a Boolean value.

• Eval Functions − The Eval functions are used in FOREACH-GENERATE statements. These functions accept a Pig value as input and return a Pig result.

• Algebraic Functions − The Algebraic functions act on inner bags in a FOREACHGENERATE statement. These functions are used to perform full MapReduce operations on an inner bag.

Eval/Filter Functions

• Each UDF must extend the EvalFunc (or) FilterFunc class
• Provide implementation to exec() function
• Create a jar file with UDF class
• Register jar file in pig script
• Define and use it 

Extend EvalFunc Class and implement exec() function

public class SimpleUDF extends EvalFunc<String>{
   
   public String exec(Tuple input) throws IOException {

      .........
     }
   } 

OR

Extend FilterFunc Class and implement exec() function

public class SimpleUDF extends FilterFunc {

    @Override
    public Boolean exec(Tuple input) throws IOException {
       ....
    }
} 

Register jar file

REGISTER '/$PIG_HOME/simpleUDF.jar'

Define the alias for simpleUDF as shown below.

DEFINE simpleUDF simpleUDF();

Use it in pig

grunt> Upper_case = FOREACH emp_data GENERATE simpleUDF(name);