Apache Pig - AVG()


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The Pig-Latin AVG() function is used to compute the average of the numerical values within a bag. While calculating the average value, the AVG() function ignores the NULL values.

Note

  • To get the global average value, we need to perform a Group All operation, and calculate the average value using the AVG() function.

  • To get the average value of a group, we need to group it using the Group By operator and proceed with the average function.

Syntax

Given below is the syntax of the AVG() function.

grunt> AVG(expression) 

Example

Assume that we have a file named student_details.txt in the HDFS directory /pig_data/ as shown below.

student_details.txt

001,Rajiv,Reddy,21,9848022337,Hyderabad,89
002,siddarth,Battacharya,22,9848022338,Kolkata,78
003,Rajesh,Khanna,22,9848022339,Delhi,90 
004,Preethi,Agarwal,21,9848022330,Pune,93 
005,Trupthi,Mohanthy,23,9848022336,Bhuwaneshwar,75 
006,Archana,Mishra,23,9848022335,Chennai,87 
007,Komal,Nayak,24,9848022334,trivendram,83 
008,Bharathi,Nambiayar,24,9848022333,Chennai,72 

And we have loaded this file into Pig with the relation name student_details as shown below.

grunt> student_details = LOAD 'hdfs://localhost:9000/pig_data/student_details.txt' USING PigStorage(',')
   as (id:int, firstname:chararray, lastname:chararray, age:int, phone:chararray, city:chararray, gpa:int);

Calculating the Average GPA

We can use the built-in function AVG() (case-sensitive) to calculate the average of a set of numerical values. Let’s group the relation student_details using the Group All operator, and store the result in the relation named student_group_all as shown below.

grunt> student_group_all = Group student_details All;

This will produce a relation as shown below.

grunt> Dump student_group_all;
   
(all,{(8,Bharathi,Nambiayar,24,9848022333,Chennai,72),
(7,Komal,Nayak,24,9848022 334,trivendram,83),
(6,Archana,Mishra,23,9848022335,Chennai,87),
(5,Trupthi,Mohan thy,23,9848022336,Bhuwaneshwar,75),
(4,Preethi,Agarwal,21,9848022330,Pune,93),
(3 ,Rajesh,Khanna,22,9848022339,Delhi,90),
(2,siddarth,Battacharya,22,9848022338,Ko lkata,78),
(1,Rajiv,Reddy,21,9848022337,Hyderabad,89)})

Let us now calculate the global average GPA of all the students using the AVG() function as shown below.

grunt> student_gpa_avg = foreach student_group_all  Generate
   (student_details.firstname, student_details.gpa), AVG(student_details.gpa); 

Verification

Verify the relation student_gpa_avg using the DUMP operator as shown below.

grunt> Dump student_gpa_avg; 

Output

It will display the contents of the relation student_gpa_avg as follows.

(({(Bharathi),(Komal),(Archana),(Trupthi),(Preethi),(Rajesh),(siddarth),(Rajiv) }, 
  {   (72)   ,  (83) ,   (87)  ,   (75)  ,   (93)  ,  (90)  ,   (78)   ,  (89)  }),83.375)
apache_pig_eval_functions.htm
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