arrow_array/array/
null_array.rs

1// Licensed to the Apache Software Foundation (ASF) under one
2// or more contributor license agreements.  See the NOTICE file
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4// regarding copyright ownership.  The ASF licenses this file
5// to you under the Apache License, Version 2.0 (the
6// "License"); you may not use this file except in compliance
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8//
9//   http://www.apache.org/licenses/LICENSE-2.0
10//
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14// KIND, either express or implied.  See the License for the
15// specific language governing permissions and limitations
16// under the License.
17
18//! Contains the `NullArray` type.
19
20use crate::builder::NullBuilder;
21use crate::{Array, ArrayRef};
22use arrow_buffer::buffer::NullBuffer;
23use arrow_data::{ArrayData, ArrayDataBuilder};
24use arrow_schema::DataType;
25use std::any::Any;
26use std::sync::Arc;
27
28/// An array of [null values](https://arrow.apache.org/docs/format/Columnar.html#null-layout)
29///
30/// A `NullArray` is a simplified array where all values are null.
31///
32/// # Example: Create an array
33///
34/// ```
35/// use arrow_array::{Array, NullArray};
36///
37/// let array = NullArray::new(10);
38///
39/// assert!(array.is_nullable());
40/// assert_eq!(array.len(), 10);
41/// assert_eq!(array.null_count(), 0);
42/// assert_eq!(array.logical_null_count(), 10);
43/// assert_eq!(array.logical_nulls().unwrap().null_count(), 10);
44/// ```
45#[derive(Clone)]
46pub struct NullArray {
47    len: usize,
48}
49
50impl NullArray {
51    /// Create a new [`NullArray`] of the specified length
52    ///
53    /// *Note*: Use [`crate::array::new_null_array`] if you need an array of some
54    /// other [`DataType`].
55    ///
56    pub fn new(length: usize) -> Self {
57        Self { len: length }
58    }
59
60    /// Returns a zero-copy slice of this array with the indicated offset and length.
61    pub fn slice(&self, offset: usize, len: usize) -> Self {
62        assert!(
63            offset.saturating_add(len) <= self.len,
64            "the length + offset of the sliced BooleanBuffer cannot exceed the existing length"
65        );
66
67        Self { len }
68    }
69
70    /// Returns a new null array builder
71    ///
72    /// Note that the `capacity` parameter to this function is _deprecated_. It
73    /// now does nothing, and will be removed in a future version.
74    pub fn builder(_capacity: usize) -> NullBuilder {
75        NullBuilder::new()
76    }
77}
78
79/// SAFETY: Correctly implements the contract of Arrow Arrays
80unsafe impl Array for NullArray {
81    fn as_any(&self) -> &dyn Any {
82        self
83    }
84
85    fn to_data(&self) -> ArrayData {
86        self.clone().into()
87    }
88
89    fn into_data(self) -> ArrayData {
90        self.into()
91    }
92
93    fn data_type(&self) -> &DataType {
94        &DataType::Null
95    }
96
97    fn slice(&self, offset: usize, length: usize) -> ArrayRef {
98        Arc::new(self.slice(offset, length))
99    }
100
101    fn len(&self) -> usize {
102        self.len
103    }
104
105    fn is_empty(&self) -> bool {
106        self.len == 0
107    }
108
109    fn offset(&self) -> usize {
110        0
111    }
112
113    fn nulls(&self) -> Option<&NullBuffer> {
114        None
115    }
116
117    fn logical_nulls(&self) -> Option<NullBuffer> {
118        (self.len != 0).then(|| NullBuffer::new_null(self.len))
119    }
120
121    fn is_nullable(&self) -> bool {
122        !self.is_empty()
123    }
124
125    fn logical_null_count(&self) -> usize {
126        self.len
127    }
128
129    fn get_buffer_memory_size(&self) -> usize {
130        0
131    }
132
133    fn get_array_memory_size(&self) -> usize {
134        std::mem::size_of::<Self>()
135    }
136}
137
138impl From<ArrayData> for NullArray {
139    fn from(data: ArrayData) -> Self {
140        let (data_type, len, nulls, _offset, buffers, _child_data) = data.into_parts();
141
142        assert_eq!(
143            data_type,
144            DataType::Null,
145            "NullArray data type should be Null"
146        );
147        assert_eq!(buffers.len(), 0, "NullArray data should contain 0 buffers");
148        assert!(
149            nulls.is_none(),
150            "NullArray data should not contain a null buffer, as no buffers are required"
151        );
152        Self { len }
153    }
154}
155
156impl From<NullArray> for ArrayData {
157    fn from(array: NullArray) -> Self {
158        let builder = ArrayDataBuilder::new(DataType::Null).len(array.len);
159        unsafe { builder.build_unchecked() }
160    }
161}
162
163impl std::fmt::Debug for NullArray {
164    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
165        write!(f, "NullArray({})", self.len())
166    }
167}
168
169#[cfg(test)]
170mod tests {
171    use super::*;
172    use crate::{Int64Array, StructArray, make_array};
173    use arrow_data::transform::MutableArrayData;
174    use arrow_schema::Field;
175
176    #[test]
177    fn test_null_array() {
178        let null_arr = NullArray::new(32);
179
180        assert_eq!(null_arr.len(), 32);
181        assert_eq!(null_arr.null_count(), 0);
182        assert_eq!(null_arr.logical_null_count(), 32);
183        assert_eq!(null_arr.logical_nulls().unwrap().null_count(), 32);
184        assert!(null_arr.is_valid(0));
185        assert!(null_arr.is_nullable());
186    }
187
188    #[test]
189    fn test_null_array_slice() {
190        let array1 = NullArray::new(32);
191
192        let array2 = array1.slice(8, 16);
193        assert_eq!(array2.len(), 16);
194        assert_eq!(array2.null_count(), 0);
195        assert_eq!(array2.logical_null_count(), 16);
196        assert_eq!(array2.logical_nulls().unwrap().null_count(), 16);
197        assert!(array2.is_valid(0));
198        assert!(array2.is_nullable());
199    }
200
201    #[test]
202    fn test_debug_null_array() {
203        let array = NullArray::new(1024 * 1024);
204        assert_eq!(format!("{array:?}"), "NullArray(1048576)");
205    }
206
207    #[test]
208    fn test_null_array_with_parent_null_buffer() {
209        let null_array = NullArray::new(1);
210        let int_array = Int64Array::from(vec![42]);
211
212        let fields = vec![
213            Field::new("a", DataType::Int64, true),
214            Field::new("b", DataType::Null, true),
215        ];
216
217        let struct_array_data = ArrayData::builder(DataType::Struct(fields.into()))
218            .len(1)
219            .add_child_data(int_array.to_data())
220            .add_child_data(null_array.to_data())
221            .build()
222            .unwrap();
223
224        let mut mutable = MutableArrayData::new(vec![&struct_array_data], true, 1);
225
226        // Simulate a NULL value in the parent array, for instance, if array being queried by
227        // invalid index
228        mutable.extend_nulls(1);
229        let data = mutable.freeze();
230
231        let struct_array = Arc::new(StructArray::from(data.clone()));
232        assert!(make_array(data) == struct_array);
233    }
234}
arrow_array/array/null_array.rs

arrow_array/array/
null_array.rs
