Struct UnionArray

pub struct UnionArray { /* private fields */ }

An array of values of varying types

Each slot in a UnionArray can have a value chosen from a number of types. Each of the possible types are named like the fields of a StructArray. A UnionArray can have two possible memory layouts, “dense” or “sparse”. For more information on please see the specification.

UnionBuilder can be used to create UnionArray’s of primitive types. UnionArray’s of nested types are also supported but not via UnionBuilder, see the tests for examples.

Examples

Create a dense UnionArray [1, 3.2, 34]

use arrow_buffer::Buffer;
use arrow_schema::*;
use std::sync::Arc;
use arrow_array::{Array, Int32Array, Float64Array, UnionArray};

let int_array = Int32Array::from(vec![1, 34]);
let float_array = Float64Array::from(vec![3.2]);
let type_id_buffer = Buffer::from_slice_ref(&[0_i8, 1, 0]);
let value_offsets_buffer = Buffer::from_slice_ref(&[0_i32, 0, 1]);

let children: Vec<(Field, Arc<dyn Array>)> = vec![
    (Field::new("A", DataType::Int32, false), Arc::new(int_array)),
    (Field::new("B", DataType::Float64, false), Arc::new(float_array)),
];

let array = UnionArray::try_new(
    &vec![0, 1],
    type_id_buffer,
    Some(value_offsets_buffer),
    children,
).unwrap();

let value = array.value(0).as_any().downcast_ref::<Int32Array>().unwrap().value(0);
assert_eq!(1, value);

let value = array.value(1).as_any().downcast_ref::<Float64Array>().unwrap().value(0);
assert!(3.2 - value < f64::EPSILON);

let value = array.value(2).as_any().downcast_ref::<Int32Array>().unwrap().value(0);
assert_eq!(34, value);

Create a sparse UnionArray [1, 3.2, 34]

use arrow_buffer::Buffer;
use arrow_schema::*;
use std::sync::Arc;
use arrow_array::{Array, Int32Array, Float64Array, UnionArray};

let int_array = Int32Array::from(vec![Some(1), None, Some(34)]);
let float_array = Float64Array::from(vec![None, Some(3.2), None]);
let type_id_buffer = Buffer::from_slice_ref(&[0_i8, 1, 0]);

let children: Vec<(Field, Arc<dyn Array>)> = vec![
    (Field::new("A", DataType::Int32, false), Arc::new(int_array)),
    (Field::new("B", DataType::Float64, false), Arc::new(float_array)),
];

let array = UnionArray::try_new(
    &vec![0, 1],
    type_id_buffer,
    None,
    children,
).unwrap();

let value = array.value(0).as_any().downcast_ref::<Int32Array>().unwrap().value(0);
assert_eq!(1, value);

let value = array.value(1).as_any().downcast_ref::<Float64Array>().unwrap().value(0);
assert!(3.2 - value < f64::EPSILON);

let value = array.value(2).as_any().downcast_ref::<Int32Array>().unwrap().value(0);
assert_eq!(34, value);

Implementations

impl UnionArray

pub unsafe fn new_unchecked( field_type_ids: &[i8], type_ids: Buffer, value_offsets: Option<Buffer>, child_arrays: Vec<(Field, ArrayRef)>, ) -> Self

Creates a new UnionArray.

Accepts type ids, child arrays and optionally offsets (for dense unions) to create a new UnionArray. This method makes no attempt to validate the data provided by the caller and assumes that each of the components are correct and consistent with each other. See try_new for an alternative that validates the data provided.

Safety

The type_ids Buffer should contain i8 values. These values should be greater than zero and must be less than the number of children provided in child_arrays. These values are used to index into the child_arrays.

The value_offsets Buffer is only provided in the case of a dense union, sparse unions should use None. If provided the value_offsets Buffer should contain i32 values. The values in this array should be greater than zero and must be less than the length of the overall array.

In both cases above we use signed integer types to maintain compatibility with other Arrow implementations.

In both of the cases above we are accepting Buffer’s which are assumed to be representing i8 and i32 values respectively. Buffer objects are untyped and no attempt is made to ensure that the data provided is valid.

pub fn try_new( field_type_ids: &[i8], type_ids: Buffer, value_offsets: Option<Buffer>, child_arrays: Vec<(Field, ArrayRef)>, ) -> Result<Self, ArrowError>

Attempts to create a new UnionArray, validating the inputs provided.

pub fn child(&self, type_id: i8) -> &ArrayRef

Accesses the child array for type_id.

Panics

Panics if the type_id provided is not present in the array’s DataType in the Union.

pub fn type_id(&self, index: usize) -> i8

Returns the type_id for the array slot at index.

Panics

Panics if index is greater than or equal to the number of child arrays

pub fn type_ids(&self) -> &ScalarBuffer<i8>

Returns the type_ids buffer for this array

pub fn offsets(&self) -> Option<&ScalarBuffer<i32>>

Returns the offsets buffer if this is a dense array

pub fn value_offset(&self, index: usize) -> usize

Returns the offset into the underlying values array for the array slot at index.

Panics

Panics if index is greater than or equal the length of the array.

pub fn value(&self, i: usize) -> ArrayRef

Returns the array’s value at index i.

Panics

Panics if index i is out of bounds

pub fn type_names(&self) -> Vec<&str>

Returns the names of the types in the union.

pub fn slice(&self, offset: usize, length: usize) -> Self

Returns a zero-copy slice of this array with the indicated offset and length.

Trait Implementations

impl Array for UnionArray

fn is_null(&self, _index: usize) -> bool

Union types always return non null as there is no validity buffer. To check validity correctly you must check the underlying vector.

fn is_valid(&self, _index: usize) -> bool

Union types always return non null as there is no validity buffer. To check validity correctly you must check the underlying vector.

fn null_count(&self) -> usize

Union types always return 0 null count as there is no validity buffer. To get null count correctly you must check the underlying vector.

fn as_any(&self) -> &dyn Any

Returns the array as Any so that it can be downcasted to a specific implementation.

fn to_data(&self) -> ArrayData

Returns the underlying data of this array

fn into_data(self) -> ArrayData

Returns the underlying data of this array

fn data_type(&self) -> &DataType

Returns a reference to the DataType of this array.

fn slice(&self, offset: usize, length: usize) -> ArrayRef

Returns a zero-copy slice of this array with the indicated offset and length.

fn len(&self) -> usize

Returns the length (i.e., number of elements) of this array.

fn is_empty(&self) -> bool

Returns whether this array is empty.

fn offset(&self) -> usize

Returns the offset into the underlying data used by this array(-slice). Note that the underlying data can be shared by many arrays. This defaults to 0.

fn nulls(&self) -> Option<&NullBuffer>

Returns the null buffer of this array if any.

fn get_buffer_memory_size(&self) -> usize

Returns the total number of bytes of memory pointed to by this array. The buffers store bytes in the Arrow memory format, and include the data as well as the validity map. Note that this does not always correspond to the exact memory usage of an array, since multiple arrays can share the same buffers or slices thereof.

fn get_array_memory_size(&self) -> usize

Returns the total number of bytes of memory occupied physically by this array. This value will always be greater than returned by get_buffer_memory_size() and includes the overhead of the data structures that contain the pointers to the various buffers.

fn logical_nulls(&self) -> Option<NullBuffer>

Returns a potentially computed NullBuffer that represents the logical null values of this array, if any.

fn is_nullable(&self) -> bool

Returns false if the array is guaranteed to not contain any logical nulls

impl Clone for UnionArray

fn clone(&self) -> UnionArray

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for UnionArray

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl From<ArrayData> for UnionArray

fn from(data: ArrayData) -> Self

Converts to this type from the input type.

impl From<UnionArray> for ArrayData

fn from(array: UnionArray) -> Self

Converts to this type from the input type.