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lttb.go
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lttb.go
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package lttb
import (
"math"
)
func LTTB(data []Point, threshold int) []Point {
if threshold >= len(data) || threshold == 0 {
return data // Nothing to do
}
sampledData := make([]Point, 0, threshold)
// 桶大小. 为开始和结束数据点留出空间
bucketSize := float64(len(data)-2) / float64(threshold-2)
sampledData = append(sampledData, data[0]) // 添加第一个点
bucketLow := 1
bucketMiddle := int(math.Floor(bucketSize)) + 1
var prevMaxAreaPoint int
for i := 0; i < threshold-2; i++ {
bucketHigh := int(math.Floor(float64(i+2)*bucketSize)) + 1
if bucketHigh >= len(data)-1 {
bucketHigh = len(data) - 2
}
// 计算下一个桶的平均点
avgPoint := calculateAverageDataPoint(data[bucketMiddle : bucketHigh+1])
// 获取当前桶的范围
currBucketStart := bucketLow
currBucketEnd := bucketMiddle
pointA := data[prevMaxAreaPoint]
maxArea := -1.0
var maxAreaPoint int
for ; currBucketStart < currBucketEnd; currBucketStart++ {
area := calculateTriangleArea(pointA, avgPoint, data[currBucketStart])
if area > maxArea {
maxArea = area
maxAreaPoint = currBucketStart
}
}
sampledData = append(sampledData, data[maxAreaPoint])
prevMaxAreaPoint = maxAreaPoint
// 移至下一个窗口
bucketLow = bucketMiddle
bucketMiddle = bucketHigh
}
sampledData = append(sampledData, data[len(data)-1]) // 添加到最后
return sampledData
}
// LTTBForBuckets - 在每个桶上应用 LTTB 算法
func LTTBForBuckets(buckets [][]Point) []Point {
bucketCount := len(buckets)
sampledData := make([]Point, 0)
sampledData = append(sampledData, buckets[0][0])
lastSelectedDataPoint := buckets[0][0]
for i := 1; i < bucketCount-1; i++ {
bucket := buckets[i]
averagePoint := calculateAveragePoint(buckets[i+1])
maxArea := -1.0
maxAreaIndex := -1
for j := 0; j < len(bucket); j++ {
point := bucket[j]
area := calculateTriangleArea(lastSelectedDataPoint, point, averagePoint)
if area > maxArea {
maxArea = area
maxAreaIndex = j
}
}
lastSelectedDataPoint := bucket[maxAreaIndex]
sampledData = append(sampledData, lastSelectedDataPoint)
}
sampledData = append(sampledData, buckets[len(buckets)-1][0])
return sampledData
}