BucketQuantile return NaN when count is ZERO

[yancl]

Hi,

When testing our service with quantile, we found that the return value is NaN when there is
no request, that means the first bucket's count is zero, so will you please return the first bucket's upperBound or zero when the count is zero ?

// change
if count == 0 {
    return bucketEnd // or 0
}
return bucketStart + (bucketEnd-bucketStart)*float64(rank/count)

//source
func bucketQuantile(q model.SampleValue, buckets buckets) float64 {
    if q < 0 {
        return math.Inf(-1)
    }
    if q > 1 {
        return math.Inf(+1)
    }
    if len(buckets) < 2 {
        return math.NaN()
    }
    sort.Sort(buckets)
    if !math.IsInf(buckets[len(buckets)-1].upperBound, +1) {
        return math.NaN()
    }

    rank := q * buckets[len(buckets)-1].count
    b := sort.Search(len(buckets)-1, func(i int) bool { return buckets[i].count >= rank })

    if b == len(buckets)-1 {
        return buckets[len(buckets)-2].upperBound
    }
    if b == 0 && buckets[0].upperBound <= 0 {
        return buckets[0].upperBound
    }
    var (
        bucketStart float64
        bucketEnd   = buckets[b].upperBound
        count       = buckets[b].count
    )
    if b > 0 {
        bucketStart = buckets[b-1].upperBound
        count -= buckets[b-1].count
        rank -= buckets[b-1].count
    }
    return bucketStart + (bucketEnd-bucketStart)*float64(rank/count)
}

[brian-brazil]

NaN is the correct result when there is no data. This is in line with _sum / _count which also returns NaN in that case.

[yancl]

ok, thanks:)

[lock]

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