Struct arrow::array::BufferBuilder [−][src]
pub struct BufferBuilder<T: ArrowNativeType> { /* fields omitted */ }
Expand description
Builder for creating a Buffer
object.
A Buffer
is the underlying data
structure of Arrow’s Arrays
.
For all supported types, there are type definitions for the
generic version of BufferBuilder<T>
, e.g. UInt8BufferBuilder
.
Example:
use arrow::array::UInt8BufferBuilder;
let mut builder = UInt8BufferBuilder::new(100);
builder.append_slice(&[42, 43, 44]);
builder.append(45);
let buffer = builder.finish();
assert_eq!(unsafe { buffer.typed_data::<u8>() }, &[42, 43, 44, 45]);
Implementations
Creates a new builder with initial capacity for at least capacity
elements of type T
.
The capacity can later be manually adjusted with the
reserve()
method.
Also the
append()
,
append_slice()
and
advance()
methods automatically increase the capacity if needed.
Example:
use arrow::array::UInt8BufferBuilder;
let mut builder = UInt8BufferBuilder::new(10);
assert!(builder.capacity() >= 10);
Returns the current number of array elements in the internal buffer.
Example:
use arrow::array::UInt8BufferBuilder;
let mut builder = UInt8BufferBuilder::new(10);
builder.append(42);
assert_eq!(builder.len(), 1);
Returns whether the internal buffer is empty.
Example:
use arrow::array::UInt8BufferBuilder;
let mut builder = UInt8BufferBuilder::new(10);
builder.append(42);
assert_eq!(builder.is_empty(), false);
Returns the actual capacity (number of elements) of the internal buffer.
Note: the internal capacity returned by this method might be larger than
what you’d expect after setting the capacity in the new()
or reserve()
functions.
Increases the number of elements in the internal buffer by n
and resizes the buffer as needed.
The values of the newly added elements are 0.
This method is usually used when appending NULL
values to the buffer
as they still require physical memory space.
Example:
use arrow::array::UInt8BufferBuilder;
let mut builder = UInt8BufferBuilder::new(10);
builder.advance(2);
assert_eq!(builder.len(), 2);
Reserves memory for at least n
more elements of type T
.
Example:
use arrow::array::UInt8BufferBuilder;
let mut builder = UInt8BufferBuilder::new(10);
builder.reserve(10);
assert!(builder.capacity() >= 20);
Appends a value of type T
into the builder,
growing the internal buffer as needed.
Example:
use arrow::array::UInt8BufferBuilder;
let mut builder = UInt8BufferBuilder::new(10);
builder.append(42);
assert_eq!(builder.len(), 1);
Appends a value of type T
into the builder N times,
growing the internal buffer as needed.
Example:
use arrow::array::UInt8BufferBuilder;
let mut builder = UInt8BufferBuilder::new(10);
builder.append_n(10, 42);
assert_eq!(builder.len(), 10);
Appends a slice of type T
, growing the internal buffer as needed.
Example:
use arrow::array::UInt8BufferBuilder;
let mut builder = UInt8BufferBuilder::new(10);
builder.append_slice(&[42, 44, 46]);
assert_eq!(builder.len(), 3);
Safety
This requires the iterator be a trusted length. This could instead require
the iterator implement TrustedLen
once that is stabilized.