arrow_array/array/null_array.rs
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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the License for the
// specific language governing permissions and limitations
// under the License.
//! Contains the `NullArray` type.
use crate::builder::NullBuilder;
use crate::{Array, ArrayRef};
use arrow_buffer::buffer::NullBuffer;
use arrow_data::{ArrayData, ArrayDataBuilder};
use arrow_schema::DataType;
use std::any::Any;
use std::sync::Arc;
/// An array of [null values](https://arrow.apache.org/docs/format/Columnar.html#null-layout)
///
/// A `NullArray` is a simplified array where all values are null.
///
/// # Example: Create an array
///
/// ```
/// use arrow_array::{Array, NullArray};
///
/// let array = NullArray::new(10);
///
/// assert!(array.is_nullable());
/// assert_eq!(array.len(), 10);
/// assert_eq!(array.null_count(), 0);
/// assert_eq!(array.logical_nulls().unwrap().null_count(), 10);
/// ```
#[derive(Clone)]
pub struct NullArray {
len: usize,
}
impl NullArray {
/// Create a new [`NullArray`] of the specified length
///
/// *Note*: Use [`crate::array::new_null_array`] if you need an array of some
/// other [`DataType`].
///
pub fn new(length: usize) -> Self {
Self { len: length }
}
/// Returns a zero-copy slice of this array with the indicated offset and length.
pub fn slice(&self, offset: usize, len: usize) -> Self {
assert!(
offset.saturating_add(len) <= self.len,
"the length + offset of the sliced BooleanBuffer cannot exceed the existing length"
);
Self { len }
}
/// Returns a new null array builder
pub fn builder(capacity: usize) -> NullBuilder {
NullBuilder::with_capacity(capacity)
}
}
impl Array for NullArray {
fn as_any(&self) -> &dyn Any {
self
}
fn to_data(&self) -> ArrayData {
self.clone().into()
}
fn into_data(self) -> ArrayData {
self.into()
}
fn data_type(&self) -> &DataType {
&DataType::Null
}
fn slice(&self, offset: usize, length: usize) -> ArrayRef {
Arc::new(self.slice(offset, length))
}
fn len(&self) -> usize {
self.len
}
fn is_empty(&self) -> bool {
self.len == 0
}
fn offset(&self) -> usize {
0
}
fn nulls(&self) -> Option<&NullBuffer> {
None
}
fn logical_nulls(&self) -> Option<NullBuffer> {
(self.len != 0).then(|| NullBuffer::new_null(self.len))
}
fn is_nullable(&self) -> bool {
!self.is_empty()
}
fn get_buffer_memory_size(&self) -> usize {
0
}
fn get_array_memory_size(&self) -> usize {
std::mem::size_of::<Self>()
}
}
impl From<ArrayData> for NullArray {
fn from(data: ArrayData) -> Self {
assert_eq!(
data.data_type(),
&DataType::Null,
"NullArray data type should be Null"
);
assert_eq!(
data.buffers().len(),
0,
"NullArray data should contain 0 buffers"
);
assert!(
data.nulls().is_none(),
"NullArray data should not contain a null buffer, as no buffers are required"
);
Self { len: data.len() }
}
}
impl From<NullArray> for ArrayData {
fn from(array: NullArray) -> Self {
let builder = ArrayDataBuilder::new(DataType::Null).len(array.len);
unsafe { builder.build_unchecked() }
}
}
impl std::fmt::Debug for NullArray {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
write!(f, "NullArray({})", self.len())
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_null_array() {
let null_arr = NullArray::new(32);
assert_eq!(null_arr.len(), 32);
assert_eq!(null_arr.null_count(), 0);
assert_eq!(null_arr.logical_nulls().unwrap().null_count(), 32);
assert!(null_arr.is_valid(0));
assert!(null_arr.is_nullable());
}
#[test]
fn test_null_array_slice() {
let array1 = NullArray::new(32);
let array2 = array1.slice(8, 16);
assert_eq!(array2.len(), 16);
assert_eq!(array2.null_count(), 0);
assert_eq!(array2.logical_nulls().unwrap().null_count(), 16);
assert!(array2.is_valid(0));
assert!(array2.is_nullable());
}
#[test]
fn test_debug_null_array() {
let array = NullArray::new(1024 * 1024);
assert_eq!(format!("{array:?}"), "NullArray(1048576)");
}
}