data: Add NilAt method to Field and Frame (#1208)

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).

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

@@ -239,6 +239,12 @@ 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]
 }