github.com/MontFerret/ferret@v0.18.0/pkg/stdlib/math/variance.go (about)

     1  package math
     2  
     3  import (
     4  	"math"
     5  
     6  	"github.com/MontFerret/ferret/pkg/runtime/core"
     7  	"github.com/MontFerret/ferret/pkg/runtime/values"
     8  	"github.com/MontFerret/ferret/pkg/runtime/values/types"
     9  )
    10  
    11  func variance(input *values.Array, sample values.Int) values.Float {
    12  	if input.Length() == 0 {
    13  		return values.NewFloat(math.NaN())
    14  	}
    15  
    16  	m, _ := mean(input)
    17  
    18  	var err error
    19  	var variance values.Float
    20  
    21  	input.ForEach(func(value core.Value, idx int) bool {
    22  		err = core.ValidateType(value, types.Int, types.Float)
    23  
    24  		if err != nil {
    25  			return false
    26  		}
    27  
    28  		n := values.Float(toFloat(value))
    29  
    30  		variance += (n - m) * (n - m)
    31  
    32  		return true
    33  	})
    34  
    35  	// When getting the mean of the squared differences
    36  	// "sample" will allow us to know if it's a sample
    37  	// or population and whether to subtract by one or not
    38  	l := values.Float(input.Length() - (1 * sample))
    39  
    40  	return variance / l
    41  }