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duration.go
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duration.go
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// Copyright 2015 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package percentile
import (
"math"
"time"
)
// An implementation of sort.Interface for durations.
type DurationSlice []time.Duration
func (p DurationSlice) Len() int { return len(p) }
func (p DurationSlice) Less(i, j int) bool { return p[i] < p[j] }
func (p DurationSlice) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
// Compute the pth percentile of vals.
//
// REQUIRES: vals is sorted.
// REQUIRES: len(vals) > 0
// REQUIRES: 0 <= p <= 100
func Duration(
vals DurationSlice,
p int) (x time.Duration) {
// We perform linear interpolation between the two closest observations based
// on the fractional part of the rank. This happens to match PERCENTIL in
// Microsoft Excel:
//
// https://en.wikipedia.org/wiki/Percentile#Microsoft_Excel_method
//
N := len(vals)
rank := (float64(p) / 100) * float64(N-1)
kFloat, d := math.Modf(rank)
k := int(kFloat)
switch {
case 0 <= k && k < N-1:
vk := float64(vals[k])
vk1 := float64(vals[k+1])
x = time.Duration(vk + d*(vk1-vk))
return
case k == N-1:
x = vals[N-1]
return
default:
panic("Invalid input")
}
}