Make MinMax return NaN when all values are NaN

Signed-off-by: Xabier Larrakoetxea <slok69@gmail.com>

internal/numbers/numbers.go

@@ -109,17 +109,20 @@ func Round(x float64) float64 {
 
 // MinMax returns the smallest and the largest value among the provided values.
 // Returns (0, 0) if there are no values.
-// Ignores NaN values.
+// Ignores NaN values. Allowing NaN values could led in a corner case where all
+// values can be NaN, in this case the function will return NaN as min and max.
 func MinMax(values []float64) (min, max float64) {
 	if len(values) == 0 {
 		return 0, 0
 	}
 	min = math.MaxFloat64
 	max = -1 * math.MaxFloat64
+	allNaN := true
 	for _, v := range values {
 		if math.IsNaN(v) {
 			continue
 		}
+		allNaN = false
 
 		if v < min {
 			min = v
@@ -128,6 +131,11 @@ func MinMax(values []float64) (min, max float64) {
 			max = v
 		}
 	}
+
+	if allNaN {
+		return math.NaN(), math.NaN()
+	}
+
 	return min, max
 }
 

internal/numbers/numbers_test.go

@@ -221,12 +221,23 @@ func TestMinMax(t *testing.T) {
 			wantMin: -11.3,
 			wantMax: 22.5,
 		},
+		{
+			desc:    "all NaN values",
+			values:  []float64{math.NaN(), math.NaN(), math.NaN(), math.NaN()},
+			wantMin: math.NaN(),
+			wantMax: math.NaN(),
+		},
 	}
 
 	for _, tc := range tests {
 		t.Run(tc.desc, func(t *testing.T) {
 			gotMin, gotMax := MinMax(tc.values)
-			if gotMin != tc.wantMin || gotMax != tc.wantMax {
+			// Different assertion for NaN cases.
+			if (math.IsNaN(tc.wantMin) && !math.IsNaN(gotMin)) ||
+				(math.IsNaN(tc.wantMax) && !math.IsNaN(gotMax)) {
+				t.Errorf("MinMax => (%v, %v), want (%v, %v)", gotMin, gotMax, tc.wantMin, tc.wantMax)
+			} else if !math.IsNaN(tc.wantMin) && gotMin != tc.wantMin ||
+				!math.IsNaN(tc.wantMax) && gotMax != tc.wantMax {
 				t.Errorf("MinMax => (%v, %v), want (%v, %v)", gotMin, gotMax, tc.wantMin, tc.wantMax)
 			}
 		})