data: Add NilAt method to Field and Frame

data/field.go

@@ -173,6 +173,15 @@ func (f *Field) At(idx int) interface{} {
 	return f.vector.At(idx)
 }
 
+// NilAt returns true if the element at index idx of the Field is nil.
+// This is useful since the interface returned by At() will not be nil
+// even if the underlying element is nil (without an type assertion).
+// It will always return false if the Field is not nullable.
+// It can panic if idx is out of range.
+func (f *Field) NilAt(idx int) bool {
+	return f.vector.NilAt(idx)
+}
+
 // Len returns the number of elements in the Field.
 // It will return 0 if the field is nil.
 func (f *Field) Len() int {

data/field_test.go

@@ -79,6 +79,19 @@ func TestFieldLen(t *testing.T) {
 	require.Equal(t, 0, f.Len())
 }
 
+func TestFieldNilAt(t *testing.T) {
+	f := data.NewField("value", nil, []*float64{nil, float64Ptr(1)})
+
+	require.True(t, f.NilAt(0))
+	require.False(t, f.At(0) == nil) // Why we have NilAt()
+	require.False(t, f.NilAt(1))
+
+	f = data.NewField("value", nil, []string{"", "foo"})
+	require.False(t, f.NilAt(1))
+	require.False(t, f.NilAt(2))
+	require.False(t, f.NilAt(77))
+}
+
 func TestField_String(t *testing.T) {
 	field := data.NewField("value", nil, make([]*string, 3))
 

data/field_type_enum.go

@@ -36,6 +36,10 @@ func (v *enumVector) At(i int) interface{} {
 	return (*v)[i]
 }
 
+func (v *enumVector) NilAt(_ int) bool {
+	return false
+}
+
 func (v *enumVector) PointerAt(i int) interface{} {
 	return &(*v)[i]
 }
@@ -115,6 +119,10 @@ func (v *nullableEnumVector) At(i int) interface{} {
 	return (*v)[i]
 }
 
+func (v *nullableEnumVector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableEnumVector) CopyAt(i int) interface{} {
 	if (*v)[i] == nil {
 		var g *EnumItemIndex

data/frame.go

@@ -240,6 +240,12 @@ func (f *Frame) Rows() int {
 	return 0
 }
 
+// NilAt returns true if the element at fieldIdx and rowIdx is nil.
+// It will panic if either fieldIdx or rowIdx are out of range.
+func (f *Frame) NilAt(fieldIdx int, rowIdx int) bool {
+	return f.Fields[fieldIdx].vector.NilAt(rowIdx)
+}
+
 // At returns the value of the specified fieldIdx and rowIdx.
 // It will panic if either fieldIdx or rowIdx are out of range.
 func (f *Frame) At(fieldIdx int, rowIdx int) interface{} {

data/generic_nullable_vector.go

@@ -34,6 +34,10 @@ func (v *nullablegenVector) Append(i interface{}) {
 	*v = append(*v, i.(*gen))
 }
 
+func (v *nullablegenVector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullablegenVector) At(i int) interface{} {
 	return (*v)[i]
 }

data/generic_vector.go

@@ -31,6 +31,10 @@ func (v *genVector) Append(i interface{}) {
 	*v = append(*v, i.(gen))
 }
 
+func (v *genVector) NilAt(i int) bool {
+	return false
+}
+
 func (v *genVector) At(i int) interface{} {
 	return (*v)[i]
 }

data/nullable_vector.gen.go

@@ -43,6 +43,10 @@ func (v *nullableUint8Vector) Append(i interface{}) {
 	*v = append(*v, i.(*uint8))
 }
 
+func (v *nullableUint8Vector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableUint8Vector) At(i int) interface{} {
 	return (*v)[i]
 }
@@ -134,6 +138,10 @@ func (v *nullableUint16Vector) Append(i interface{}) {
 	*v = append(*v, i.(*uint16))
 }
 
+func (v *nullableUint16Vector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableUint16Vector) At(i int) interface{} {
 	return (*v)[i]
 }
@@ -225,6 +233,10 @@ func (v *nullableUint32Vector) Append(i interface{}) {
 	*v = append(*v, i.(*uint32))
 }
 
+func (v *nullableUint32Vector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableUint32Vector) At(i int) interface{} {
 	return (*v)[i]
 }
@@ -316,6 +328,10 @@ func (v *nullableUint64Vector) Append(i interface{}) {
 	*v = append(*v, i.(*uint64))
 }
 
+func (v *nullableUint64Vector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableUint64Vector) At(i int) interface{} {
 	return (*v)[i]
 }
@@ -407,6 +423,10 @@ func (v *nullableInt8Vector) Append(i interface{}) {
 	*v = append(*v, i.(*int8))
 }
 
+func (v *nullableInt8Vector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableInt8Vector) At(i int) interface{} {
 	return (*v)[i]
 }
@@ -498,6 +518,10 @@ func (v *nullableInt16Vector) Append(i interface{}) {
 	*v = append(*v, i.(*int16))
 }
 
+func (v *nullableInt16Vector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableInt16Vector) At(i int) interface{} {
 	return (*v)[i]
 }
@@ -589,6 +613,10 @@ func (v *nullableInt32Vector) Append(i interface{}) {
 	*v = append(*v, i.(*int32))
 }
 
+func (v *nullableInt32Vector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableInt32Vector) At(i int) interface{} {
 	return (*v)[i]
 }
@@ -680,6 +708,10 @@ func (v *nullableInt64Vector) Append(i interface{}) {
 	*v = append(*v, i.(*int64))
 }
 
+func (v *nullableInt64Vector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableInt64Vector) At(i int) interface{} {
 	return (*v)[i]
 }
@@ -771,6 +803,10 @@ func (v *nullableFloat32Vector) Append(i interface{}) {
 	*v = append(*v, i.(*float32))
 }
 
+func (v *nullableFloat32Vector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableFloat32Vector) At(i int) interface{} {
 	return (*v)[i]
 }
@@ -862,6 +898,10 @@ func (v *nullableFloat64Vector) Append(i interface{}) {
 	*v = append(*v, i.(*float64))
 }
 
+func (v *nullableFloat64Vector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableFloat64Vector) At(i int) interface{} {
 	return (*v)[i]
 }
@@ -953,6 +993,10 @@ func (v *nullableStringVector) Append(i interface{}) {
 	*v = append(*v, i.(*string))
 }
 
+func (v *nullableStringVector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableStringVector) At(i int) interface{} {
 	return (*v)[i]
 }
@@ -1044,6 +1088,10 @@ func (v *nullableBoolVector) Append(i interface{}) {
 	*v = append(*v, i.(*bool))
 }
 
+func (v *nullableBoolVector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableBoolVector) At(i int) interface{} {
 	return (*v)[i]
 }
@@ -1135,6 +1183,10 @@ func (v *nullableTimeTimeVector) Append(i interface{}) {
 	*v = append(*v, i.(*time.Time))
 }
 
+func (v *nullableTimeTimeVector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableTimeTimeVector) At(i int) interface{} {
 	return (*v)[i]
 }
@@ -1226,6 +1278,10 @@ func (v *nullableJsonRawMessageVector) Append(i interface{}) {
 	*v = append(*v, i.(*json.RawMessage))
 }
 
+func (v *nullableJsonRawMessageVector) NilAt(i int) bool {
+	return (*v)[i] == nil
+}
+
 func (v *nullableJsonRawMessageVector) At(i int) interface{} {
 	return (*v)[i]
 }