3.3 Counts and Sums

The static Count() method on class StatsFunctions returns the number of elements in a data set:

int numElements = StatsFunctions.Count( data );

Counts() returns an IDictionary of key-value pairs in which the keys are the unique elements in a given data set, and the values are the counts for each element.

CountIf() calculates how many elements in a data set return true when a logical function is applied. For example, suppose MeetsThreshold() is a method that returns true if a given numeric value is greater than 100:

public bool MeetsThreshold( double x )
{
  return ( x > 100 );
}

This code counts the number of elements in a data set that meet the criterion:

int num = StatsFunctions.CountIf( data, new 
  StatsFunctions.LogicalDoubleFunction( MeetsThreshold ) );

Similarly, the static Sum() method sums the elements in a data set. SumIf() sums the elements in a data set that return true when a logical function is applied:

double sum = StatsFunctions.SumIf( data, new 
  StatsFunctions.LogicalDoubleFunction( MeetsThreshold ) );

An overload of SumIf() sums the elements in one data set based on evaluating a logical function on another data set. For instance, this code sums the elements in data2 that correspond to those elements in data where MeetsThreshold() returns true:

double sum = StatsFunctions.SumIf( data, function, data2 );

A MismatchedSizeException is raised if the two data sets do not have the same number of elements.

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