// Slices the data into sections, returning a slice of float64s.
// Returns an error if the data set is empty.
func (q Quartile) Transform(analyzer *mino.Analyzer, data mino.Collection) (interface{}, error) {
sections := q.Sections
if sections == 0 {
sections = 4
}
results := make([]float64, sections-1)
dividend := (1 + data.Weight()) / float64(sections)
// todo(connor4312): my algorithm below behaves oddly when the data
// size is less than the number of requested sections. Whoever discovers
// a solution to it is awarded three cookies.
if data.Len() < sections {
return results, InsufficientDataError
}
data.Sort(func(a, b mino.DataPoint) bool {
return a.Value < b.Value
})
var weight float64
var prev mino.DataPoint
SECTION:
for i := 1; i < sections; i++ {
target := float64(i) * dividend
for data.HasMore() {
current := data.Next()
last := prev
prev = current
if weight+current.Weight > target {
frac := (target - weight) / current.Weight
results[i-1] = last.Value*(1-frac) + current.Value*frac
data.Rewind(1)
continue SECTION
}
weight += current.Weight
}
results[i-1] = prev.Value
}
return results, nil
}
