feat(helper/SummarizeValues): support stddev function

.github/workflows/ci.yml

@@ -26,7 +26,9 @@ jobs:
           /usr/local/bin/go version
           echo "PATH=$HOME/go/bin:$HOME/sdk/gotip/bin/:$PATH" >> $GITHUB_ENV
       - name: install cairo
-        run: sudo apt-get install libcairo2-dev -y
+        run: |
+          sudo apt-get update
+          sudo apt-get install libcairo2-dev -y
       - name: checkout code
         uses: actions/checkout@v5
       - name: test

pkg/expr/helper/helper.go

@@ -245,6 +245,9 @@ func SummarizeValues(f string, values []float64, absent []bool) (float64, bool,
 	case "median":
 		val, abs := Percentile(values, 50, true)
 		return val, abs, nil
+	case "stddev":
+		rv = math.Sqrt(VarianceValue(values, absent))
+		return rv, false, nil
 	default:
 		looks_like_percentile, err := regexp.MatchString(`^p\d\d?$`, f)
 		if err != nil {

pkg/expr/helper/helper_test.go

@@ -1,6 +1,7 @@
 package helper
 
 import (
+	"math"
 	"testing"
 )
 
@@ -27,3 +28,234 @@ func TestPercentile(t *testing.T) {
 		}
 	}
 }
+
+func TestSummarizeValues(t *testing.T) {
+	tests := []struct {
+		name     string
+		function string
+		values   []float64
+		absent   []bool
+		expected float64
+		isAbsent bool
+		wantErr  bool
+	}{
+		{
+			name:     "sum with all values",
+			function: "sum",
+			values:   []float64{1, 2, 3, 4, 5},
+			absent:   []bool{false, false, false, false, false},
+			expected: 15,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "total with all values",
+			function: "total",
+			values:   []float64{10, 20, 30},
+			absent:   []bool{false, false, false},
+			expected: 60,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "avg with all values",
+			function: "avg",
+			values:   []float64{2, 4, 6, 8},
+			absent:   []bool{false, false, false, false},
+			expected: 5,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "average with some absent",
+			function: "average",
+			values:   []float64{10, 20, 30, 40},
+			absent:   []bool{false, true, false, false},
+			expected: 26.666666666666668,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "max with all values",
+			function: "max",
+			values:   []float64{1, 5, 3, 9, 2},
+			absent:   []bool{false, false, false, false, false},
+			expected: 9,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "min with all values",
+			function: "min",
+			values:   []float64{5, 2, 8, 1, 9},
+			absent:   []bool{false, false, false, false, false},
+			expected: 1,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "min with some absent",
+			function: "min",
+			values:   []float64{5, 2, 8, 1, 9},
+			absent:   []bool{false, true, false, false, false},
+			expected: 1,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "last with all values",
+			function: "last",
+			values:   []float64{1, 2, 3, 4, 5},
+			absent:   []bool{false, false, false, false, false},
+			expected: 5,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "last with trailing absent",
+			function: "last",
+			values:   []float64{1, 2, 3, 4, 5},
+			absent:   []bool{false, false, false, false, true},
+			expected: 4,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "count with all values",
+			function: "count",
+			values:   []float64{1, 2, 3, 4, 5},
+			absent:   []bool{false, false, false, false, false},
+			expected: 5,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "count with some absent",
+			function: "count",
+			values:   []float64{1, 2, 3, 4, 5},
+			absent:   []bool{false, true, false, true, false},
+			expected: 3,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "median with odd count",
+			function: "median",
+			values:   []float64{1, 2, 3, 4, 5},
+			absent:   []bool{false, false, false, false, false},
+			expected: 3,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "median with even count",
+			function: "median",
+			values:   []float64{1, 2, 3, 4},
+			absent:   []bool{false, false, false, false},
+			expected: 2.5,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "stddev with simple values",
+			function: "stddev",
+			values:   []float64{2, 4, 4, 4, 5, 5, 7, 9},
+			absent:   []bool{false, false, false, false, false, false, false, false},
+			expected: 2,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "stddev with all same values",
+			function: "stddev",
+			values:   []float64{5, 5, 5, 5, 5},
+			absent:   []bool{false, false, false, false, false},
+			expected: 0,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "stddev with some absent",
+			function: "stddev",
+			values:   []float64{2, 4, 4, 4, 5, 5, 7, 9},
+			absent:   []bool{false, true, false, false, false, false, false, false},
+			expected: 2.099562636671296,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "empty values",
+			function: "sum",
+			values:   []float64{},
+			absent:   []bool{},
+			expected: 0,
+			isAbsent: true,
+			wantErr:  false,
+		},
+		{
+			name:     "percentile p50",
+			function: "p50",
+			values:   []float64{1, 2, 3, 4, 5},
+			absent:   []bool{false, false, false, false, false},
+			expected: 3,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "percentile p95",
+			function: "p95",
+			values:   []float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10},
+			absent:   []bool{false, false, false, false, false, false, false, false, false, false},
+			expected: 9.55,
+			isAbsent: false,
+			wantErr:  false,
+		},
+		{
+			name:     "unsupported function",
+			function: "invalid",
+			values:   []float64{1, 2, 3},
+			absent:   []bool{false, false, false},
+			expected: 0,
+			isAbsent: true,
+			wantErr:  true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, isAbsent, err := SummarizeValues(tt.function, tt.values, tt.absent)
+
+			if (err != nil) != tt.wantErr {
+				t.Errorf("SummarizeValues() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+
+			if tt.wantErr {
+				return
+			}
+
+			if isAbsent != tt.isAbsent {
+				t.Errorf("SummarizeValues() isAbsent = %v, want %v", isAbsent, tt.isAbsent)
+			}
+
+			if !tt.isAbsent && !almostEqual(got, tt.expected) {
+				t.Errorf("SummarizeValues() got = %v, want %v", got, tt.expected)
+			}
+		})
+	}
+}
+
+// almostEqual checks if two float64 values are approximately equal
+func almostEqual(a, b float64) bool {
+	const epsilon = 1e-9
+	if math.IsNaN(a) && math.IsNaN(b) {
+		return true
+	}
+	if math.IsInf(a, 1) && math.IsInf(b, 1) {
+		return true
+	}
+	if math.IsInf(a, -1) && math.IsInf(b, -1) {
+		return true
+	}
+	return math.Abs(a-b) < epsilon
+}