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What is LOG() function?

  • In mathematics, the logarithm is the inverse operation to exponentiation, just as division is the inverse of multiplication and vice versa.
  • That means the logarithm of a number is the exponent to which another fixed number, the base, must be raised to produce that number.
  • In simple cases the logarithm counts factors in multiplication.
  • For example, the base 10 logarithm of 1000 is 3, as 10 to the power 3 is 1000 (1000 = 10 × 10 × 10 = 10^3); 10 is used as a factor three times.
 Apache Pig Log

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LOG() function in Apache Pig

  • The LOG() function of Pig Latin is used to calculate the natural logarithm (base e) value of a given expression.
  • Returns the natural logarithm (base e) of an expression.

Syntax

grunt> LOG(expression)

Example

  • Ensure that we have a file named wikitechy_math.txt in the HDFS directory /pig_data/.
  • This file contains integer and floating point values as given below.

wikitechy_math.txt

8
19 
12 
5.8 
8.7 
5.1 
  • You have loaded this file into Pig with a relation named math_data as given below.
grunt> math_data = LOAD 'hdfs://localhost:9000/pig_data/wikitechy_math.txt' USING PigStorage(',')
   as (data:float);
  • Now calculate the log values of the contents of the wikitechy_math.txtfile using LOG() function as given below.
grunt> log_data = foreach math_data generate (data),LOG(data);

Verification

  • Now verify the contents of the relation using the Dump operator as given below.
grunt> Dump log_data;

Output

  • The above statement stores the result in the relation named log_data.
(5.0,1.6094379124341003) 
(16.0,2.772588722239781) 
(9.0,2.1972245773362196) 
(2.5,0.9162907318741551) 
(5.9,1.774952367075645) 
(3.1,1.1314020807274126)

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