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feat: linreg => slope 0 for const values (#9728)
* feat: linreg => slope 0 for const values Signed-off-by: mtfoley <mtfoley.mae@gmail.com>
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@ -716,8 +716,16 @@ func linearRegression(samples []Point, interceptTime int64) (slope, intercept fl
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sumY, cY float64
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sumXY, cXY float64
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sumX2, cX2 float64
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initY float64
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constY bool
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)
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for _, sample := range samples {
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initY = samples[0].V
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constY = true
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for i, sample := range samples {
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// Set constY to false if any new y values are encountered.
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if constY && i > 0 && sample.V != initY {
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constY = false
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}
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n += 1.0
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x := float64(sample.T-interceptTime) / 1e3
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sumX, cX = kahanSumInc(x, sumX, cX)
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@ -725,7 +733,12 @@ func linearRegression(samples []Point, interceptTime int64) (slope, intercept fl
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sumXY, cXY = kahanSumInc(x*sample.V, sumXY, cXY)
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sumX2, cX2 = kahanSumInc(x*x, sumX2, cX2)
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}
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if constY {
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if math.IsInf(initY, 0) {
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return math.NaN(), math.NaN()
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}
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return 0, initY
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}
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sumX = sumX + cX
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sumY = sumY + cY
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sumXY = sumXY + cXY
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@ -44,8 +44,14 @@ func TestDeriv(t *testing.T) {
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a := storage.Appender(context.Background())
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metric := labels.FromStrings("__name__", "foo")
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a.Append(0, metric, 1493712816939, 1.0)
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a.Append(0, metric, 1493712846939, 1.0)
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start := 1493712816939
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interval := 30 * 1000
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// Introduce some timestamp jitter to test 0 slope case.
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// https://github.com/prometheus/prometheus/issues/7180
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for i := 0; i < 15; i++ {
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jitter := 12 * i % 2
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a.Append(0, metric, int64(start+interval*i+jitter), 1)
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}
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require.NoError(t, a.Commit())
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