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Perf: Eliminate LINQ allocations in BoxAndWhiskerSeries.GenerateSegments #370

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Merged
PaulAndersonS merged 2 commits into from
May 27, 2026
+35 −2
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Perf: Eliminate LINQ allocations in BoxAndWhiskerSeries.GenerateSegments #370

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Perf: Eliminate LINQ allocations in BoxAndWhiskerSeries.GenerateSegments
PaulAndersonS May 26, 2026
bf78a29
Merge branch 'main' into paulandersons/perf-daily-performance-improve…
SaiyathAliFathima May 27, 2026
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37 changes: 35 additions & 2 deletions maui/src/Charts/Series/BoxAndWhiskerSeries.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1034,15 +1034,21 @@ internal override void GenerateSegments(SeriesView seriesView)

for (int i = 0; i < PointsCount; i++)
{
var yList = YDataCollection[i].Where(x => !double.IsNaN(x)).ToArray();
var yList = FilterNaNValues(YDataCollection[i]);

List<double> outliers = [];

if (yList.Length > 0)
{
// The quartile, whisker, and min/max calculations below all rely on ascending values.
Array.Sort(yList);
average = yList.Average();
double sum = 0;
for (int j = 0; j < yList.Length; j++)
{
sum += yList[j];
}

average = sum / yList.Length;
}

int yCount = yList.Length;
Expand Down Expand Up @@ -1489,6 +1495,33 @@ static void GetMinMaxandOutlier(double lowerQuartile, double upperQuartile, doub
}
}

/// <summary>
/// Filters out NaN values from the source list without LINQ allocations.
/// </summary>
static double[] FilterNaNValues(IList<double> source)
{
int count = 0;
for (int i = 0; i < source.Count; i++)
{
if (!double.IsNaN(source[i]))
{
count++;
}
}

var result = new double[count];
int index = 0;
for (int i = 0; i < source.Count; i++)
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@SaiyathAliFathima SaiyathAliFathima May 27, 2026

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Why does FilterNaNValues(IList source) use two for loops (one to count valid values, then one to copy them) so that double.IsNaN is checked twice for each element, instead of using a single-pass approach?

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@PaulAndersonS PaulAndersonS May 27, 2026

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@copilot Check this feedback

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Copilot AI May 27, 2026

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The two-pass version is intentional because this helper returns a double[] with exact length while avoiding LINQ/list allocations. In a true single-pass approach, we’d either use List<double> (extra object + ToArray copy) or allocate source.Count and then resize/copy. For this hot path, avoiding those extra allocations/copies was prioritized over the extra IsNaN check.

{
if (!double.IsNaN(source[i]))
{
result[index++] = source[i];
}
}

return result;
}

void GetQuartileValues(double[] yList, int len, out double lowerQuartile, out double upperQuartile)
{
double[] lowerQuartileArray;
Expand Down