Package edu.caltech.nanodb.functions

Class StdDevVarAggregate

  • All Implemented Interfaces:
    java.lang.Cloneable
    Direct Known Subclasses:
    StdDev, Variance
    public class StdDevVarAggregate
extends AggregateFunction
    This aggregate function can be used to compute either the standard deviation or the variance of a collection of values.

    • Field Summary

      Fields 
      Modifier and Type Field Description
      private boolean computeStdDev  
      private java.lang.Object sum  
      private java.util.ArrayList<java.lang.Object> values  

    • Constructor Summary

      Constructors 
      Constructor Description
      StdDevVarAggregate​(boolean computeStdDev)  

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void addValue​(java.lang.Object value)
      Adds a value to the aggregate function so that it can update its internal state.
      void clearResult()
      Clears the aggregate function's current state so that the object can be reused to compute an aggregate on another set of input values.
      java.lang.Object getResult()
      Returns the aggregated result computed for this aggregate function.
      ColumnType getReturnType​(java.util.List<Expression> args, Schema schema)
      Returns the column type of the resulting column after applying the function.
      private java.lang.Object squareDifference​(java.lang.Object value, java.lang.Object avg)
      Helper function that computes the square of the difference between two values.

      • Methods inherited from class edu.caltech.nanodb.functions.Function

        clone

      • Methods inherited from class java.lang.Object

        equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Field Detail

      • computeStdDev

        private boolean computeStdDev

      • sum

        private java.lang.Object sum

      • values

        private java.util.ArrayList<java.lang.Object> values

    • Constructor Detail

      • StdDevVarAggregate

        public StdDevVarAggregate​(boolean computeStdDev)

    • Method Detail

      • clearResult

        public void clearResult()
        Description copied from class: AggregateFunction
        Clears the aggregate function's current state so that the object can be reused to compute an aggregate on another set of input values.
        Specified by:
        clearResult in class AggregateFunction

      • addValue

        public void addValue​(java.lang.Object value)
        Description copied from class: AggregateFunction
        Adds a value to the aggregate function so that it can update its internal state. Generally, aggregate functions ignore null inputs (which represent SQL NULL values) when computing their results.
        Specified by:
        addValue in class AggregateFunction
        Parameters:
        value - the value to add to the aggregate function

      • getResult

        public java.lang.Object getResult()
        Description copied from class: AggregateFunction
        Returns the aggregated result computed for this aggregate function. Generally, if aggregate functions receive no non-null inputs then they should produce a null result. (COUNT is an exception to this rule, producing 0 in that case.)
        Specified by:
        getResult in class AggregateFunction
        Returns:
        the result of the aggregate computation.

      • getReturnType

        public ColumnType getReturnType​(java.util.List<Expression> args,
                                Schema schema)
        Description copied from class: ScalarFunction
        Returns the column type of the resulting column after applying the function. This generally depends on the column type of the inputs.
        Specified by:
        getReturnType in class ScalarFunction
        Parameters:
        args - the arguments to the function call
        schema - the schema of the table
        Returns:
        the column type of the resulting column

      • squareDifference

        private java.lang.Object squareDifference​(java.lang.Object value,
                                          java.lang.Object avg)
        Helper function that computes the square of the difference between two values.