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What is Limit Operator in Apache Pig ?

  • The LIMIT operator is used to get a limited number of tuples from a relation.
  • This idea has come to mind visualizing the fact that " 'ddx' is an operator and derivative of a function is defined by 'Limit'".
  • Well, the limit as x approaches something is an operator, such as limx→0.
  • LIMIT instruction:
    • Truncates relation’s size
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    Syntax

    grunt> Result = LIMIT Relation_name required number of tuples;
    

    Example

    • Ensure that we have a file named wikitechy_employee_details.txt in the HDFS directory /pig_data/ as given below.

    wikitechy_employee_details.txt

    111,Anu,Shankar,23,9876543210,Chennai
    112,Barvathi,Nambiayar,24,9876543211,Chennai
    113,Kajal,Nayak,24,9876543212,Trivendram
    114,Preethi,Antony,21,9876543213,Pune
    115,Raj,Gopal,21,9876543214,Hyderabad
    116,Yashika,Kannan,22,9876543215,Delhi
    117,siddu,Narayanan,22,9876543216,Kolkata
    118,Timple,Mohanthy,23,9876543217,Bhuwaneshwar
    
    • You have loaded this file into Pig with the relation name wikitechy_employee_details as given below.
    grunt>wikitechy_employee_details = LOAD 'hdfs://localhost:9000/pig_data/ wikitechy_employee_details.txt' USING PigStorage(',')
       as (id:int, firstname:chararray, lastname:chararray,age:int, phone:chararray, city:chararray);
    
    • Sort the relation in descending order based on the age of the employee and store it into another relation named limit_data using the ORDER BY operator as given below.
    grunt> limit_data = LIMIT wikitechy_employee_details 4; 
    

    Verification

    • Now verify the relation limit_data using the DUMP operator as shown below.
    grunt> Dump limit_data; 
    

    Output

    • The following output, display the contents of the relation limit_data.
    111,Anu,Shankar,23,9876543210,Chennai
    112,Barvathi,Nambiayar,24,9876543211,Chennai
    113,Kajal,Nayak,24,9876543212,Trivendram
    114,Preethi,Antony,21,9876543213,Pune
    

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