NMath User's Guide

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38.3 Counts and Sums (.NET, C#, CSharp, VB, Visual Basic, F#)

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

Code Example – C#

int numElements = StatsFunctions.Count( data );

Code Example – VB

Dim NumElements As Integer = 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:

Code Example – C#

public bool MeetsThreshold( double x )

{

  return ( x > 100 );

}

Code Example – VB

Public Function MeetsThreshold(X As Double) As Boolean

  Return (X > 100)

End Function

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

Code Example – C#

int num = StatsFunctions.CountIf( data, new 

  new Func<double, bool>( MeetsThreshold ) );

Code Example – VB

Dim Num As Integer = StatsFunctions.CountIf(DataArray,

  New Func(Of Double, Boolean)(AddressOf 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:

Code Example – C#

double sum = StatsFunctions.SumIf( data, new 

  new Func<double, bool>( MeetsThreshold ) );

Code Example – VB

Dim Sum As Double = StatsFunctions.SumIf(DataColumn,

  New Func(Of Double, Boolean)(AddressOf 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:

Code Example – C#

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

Code Example – VB

Dim Sum As Double = StatsFunctions.SumIf(DataVector, MyFunction, 

  data2)

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


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