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What is Eval Functions in Apache Pig ?
- Eval functions extend the Java class ‘org.apache.pig.EvalFunc and it is parameterized with the return type of the UDF which is a Java String which is a part of java class
- Eval Functions will take one record and returns one result, which will be invoked for every record that will pass through the execution pipeline.
- Eval Function takes the tuple which contains the fields for the script which is passed to the UDF (User Defined Function) as an input.
- Eval function is invoked on every input tuple and the input is done into the function which is a tuple with input parameters where they are passed to the function which is done in the Pig script.
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An example which is given below done to explain the Eval Functions
The table which is given below give us the eval functions and their description
|AVG||AVG(expression||Computes the average of the numeric values in a single-column bag.|
|CONCAT||CONCAT (expression, expression)||Concatenates two expressions of identical type.|
|COUNT||COUNT(expression)||Computes the number of elements in a bag, it ignores null.|
|COUNT_STAR||COUNT_STAR(expression)||Computes the number of elements in a bag, it includes null.|
|DIFF||DIFF (expression, expression)||Compares two fields in a tuple, any tuples that are in one bag but not the other are returned in a bag.|
|IsEmpty||IsEmpty(expression)||Checks if a bag or map is empty|
|MAX||MAX(expression)||Computes the maximum of the numeric values or chararrays in a single-column bag|
|MIN||MIN(expression)||Computes the minimum of the numeric values or chararrays in a single-column bag.|
|SIZE||SIZE(expression)||Computes the number of elements based on any Pig data type. SIZE includes NULL values in the size computation|
|SUM||SUM(expression)||Computes the sum of the numeric values in a single-column bag.|
|TOKENIZE||TOKENIZE(expression [, ‘field_delimiter’])||Splits a string and outputs a bag of words.|