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Fix percentile computation #72

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Fix percentile computation #72

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2 changes: 1 addition & 1 deletion data_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -166,7 +166,7 @@ func assertPercentiles(fn func(i float64) (float64, error), i float64, f float64
}

func TestPercentileMethods(t *testing.T) {
assertPercentiles(data1.Percentile, 75, 4.2, t)
assertPercentiles(data1.Percentile, 75, 4.4, t)
assertPercentiles(data1.PercentileNearestRank, 75, 4.2, t)

}
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32 changes: 13 additions & 19 deletions percentile.go
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Original file line number Diff line number Diff line change
Expand Up @@ -11,39 +11,33 @@ func Percentile(input Float64Data, percent float64) (percentile float64, err err
return math.NaN(), EmptyInputErr
}

if length == 1 {
return input[0], nil
}

if percent <= 0 || percent > 100 {
if percent < 0 || percent > 100 {
return math.NaN(), BoundsErr
}

// Start by sorting a copy of the slice
c := sortedCopy(input)

// Multiply percent by length of input
index := (percent / 100) * float64(len(c))
// Calculate rank
rank := (percent / 100) * float64(len(c)-1)

// Check if the index is a whole number
if index == float64(int64(index)) {
// Convert float to int
ri := int(rank)

// Convert float to int
i := int(index)
// Check if the index is a whole number
if rank == float64(ri) {

// Find the value at the index
percentile = c[i-1]
percentile = c[ri]

} else if index > 1 {
} else {

// Convert float to int via truncation
i := int(index)
// Calculate the fractional part of the rank
rf := rank - float64(ri)

// Find the average of the index and following values
percentile, _ = Mean(Float64Data{c[i-1], c[i]})
// Interpolate
percentile = c[ri] + rf*(c[ri+1]-c[ri])

} else {
return math.NaN(), BoundsErr
}

return percentile, nil
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113 changes: 103 additions & 10 deletions percentile_test.go
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Original file line number Diff line number Diff line change
@@ -1,12 +1,104 @@
package stats_test

import (
"math"
"reflect"
"testing"

"github.com/montanaflynn/stats"
)

func round(value float64) float64 {
return math.Round(value*100) / 100
}

func TestPercentileOneToTen(t *testing.T) {
m, _ := stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 0)
if m != 1 {
t.Errorf("%.1f != %.1f", m, 1.0)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 5)
if m != 1.45 {
t.Errorf("%.2f != %.2f", m, 1.45)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 10)
if m != 1.9 {
t.Errorf("%.1f != %.1f", m, 1.9)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 15)
if round(m) != 2.35 {
t.Errorf("%.2f != %.2f", m, 2.35)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 20)
if m != 2.8 {
t.Errorf("%.1f != %.1f", m, 2.8)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 25)
if m != 3.25 {
t.Errorf("%.1f != %.1f", m, 3.25)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 30)
if round(m) != 3.7 {
t.Errorf("%.1f != %.1f", m, 3.7)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 35)
if m != 4.15 {
t.Errorf("%.1f != %.1f", m, 4.15)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 40)
if m != 4.6 {
t.Errorf("%.1f != %.1f", m, 4.6)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 45)
if m != 5.05 {
t.Errorf("%.1f != %.1f", m, 5.05)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 50)
if m != 5.5 {
t.Errorf("%.1f != %.1f", m, 5.5)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 55)
if m != 5.95 {
t.Errorf("%.1f != %.1f", m, 5.95)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 60)
if round(m) != 6.4 {
t.Errorf("%.1f != %.1f", m, 6.4)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 65)
if round(m) != 6.85 {
t.Errorf("%.1f != %.1f", m, 6.85)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 70)
if m != 7.3 {
t.Errorf("%.1f != %.1f", m, 7.3)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 75)
if m != 7.75 {
t.Errorf("%.1f != %.1f", m, 7.75)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 80)
if m != 8.2 {
t.Errorf("%.1f != %.1f", m, 8.2)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 85)
if round(m) != 8.65 {
t.Errorf("%.1f != %.1f", m, 8.65)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 90)
if m != 9.1 {
t.Errorf("%.1f != %.1f", m, 9.1)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 95)
if round(m) != 9.55 {
t.Errorf("%.1f != %.1f", m, 9.55)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 100)
if m != 10.0 {
t.Errorf("%.1f != %.1f", m, 10.0)
}
}

func TestPercentile(t *testing.T) {
m, _ := stats.Percentile([]float64{43, 54, 56, 61, 62, 66}, 90)
if m != 64.0 {
Expand All @@ -17,12 +109,13 @@ func TestPercentile(t *testing.T) {
t.Errorf("%.1f != %.1f", m, 43.0)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 50)
if m != 5.0 {
t.Errorf("%.1f != %.1f", m, 5.0)
median, _ := stats.Median([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10})
if m != median || m != 5.5 {
t.Errorf("%.1f != %.1f", m, 5.5)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 99.9)
if m != 9.5 {
t.Errorf("%.1f != %.1f", m, 9.5)
if round(m) != 9.99 {
t.Errorf("%.2f != %.2f", m, 9.91)
}
m, _ = stats.Percentile([]float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 100)
if m != 10.0 {
Expand All @@ -32,13 +125,13 @@ func TestPercentile(t *testing.T) {
if err != stats.EmptyInputErr {
t.Errorf("Empty slice didn't return expected error; got %v", err)
}
_, err = stats.Percentile([]float64{1, 2, 3, 4, 5}, 0)
if err != stats.BoundsErr {
t.Errorf("Zero percent didn't return expected error; got %v", err)
m, err = stats.Percentile([]float64{1, 2, 3, 4, 5}, 0)
if m != 1.0 {
t.Errorf("%.1f != %.1f", m, 1.0)
}
_, err = stats.Percentile([]float64{1, 2, 3, 4, 5}, 0.13)
if err != stats.BoundsErr {
t.Errorf("Too low percent didn't return expected error; got %v", err)
m, err = stats.Percentile([]float64{1, 2, 3, 4, 5}, 0.13)
if round(m) != 1.01 {
t.Errorf("%.2f != %.2f", m, 1.0)
}
_, err = stats.Percentile([]float64{1, 2, 3, 4, 5}, 101)
if err != stats.BoundsErr {
Expand Down