Merge pull request #27 from RedisGraph/fix.sample.cdf

In case of CDF vs random leads to after last bucket ensure that bucket pos is correct

multi-query.go

@@ -10,9 +10,12 @@ import (
 func sample(cdf []float32) int {
 	r := rand.Float32()
 	bucket := 0
-	for r > cdf[bucket] {
+	for (bucket < len(cdf)) && (r > cdf[bucket]) {
 		bucket++
 	}
+	if bucket >= len(cdf) {
+		bucket = bucket - 1
+	}
 	return bucket
 }
 

multi-query_test.go

@@ -0,0 +1,26 @@
+package main
+
+import "testing"
+
+func Test_sample(t *testing.T) {
+	type args struct {
+		cdf []float32
+	}
+	tests := []struct {
+		name string
+		args args
+		want int
+	}{
+		{name: "last bucket", args: args{[]float32{0.01, 0.99}}, want: 1},
+		{name: "last bucket with high likelyhood", args: args{[]float32{0.00001, 0.99}}, want: 1},
+		{name: "single bucket", args: args{[]float32{0.99}}, want: 0},
+		{name: "after bucket", args: args{[]float32{0.00000001}}, want: 0},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := sample(tt.args.cdf); got != tt.want {
+				t.Errorf("sample() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}