Encoding

Files
file	encode.hpp
	Dictionary column encode and decode APIs.

Functions
std::unique_ptr< column >	cudf::dictionary::encode (column_view const &column, data_type indices_type=data_type{type_id::UINT32}, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Construct a dictionary column by dictionary encoding an existing column. More...
std::unique_ptr< column >	cudf::dictionary::decode (dictionary_column_view const &dictionary_column, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Create a column by gathering the keys from the provided dictionary_column into a new column using the indices from that column. More...

Detailed Description

Function Documentation

decode()

std::unique_ptr<column> cudf::dictionary::decode	(	dictionary_column_view const &	dictionary_column,
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Create a column by gathering the keys from the provided dictionary_column into a new column using the indices from that column.

d1 = {["a", "c", "d"], [2, 0, 1, 0]}
s = decode(d1)
s is now ["d", "a", "c", "a"]

Parameters

dictionary_column	Existing dictionary column
stream	CUDA stream used for device memory operations and kernel launches
mr	Device memory resource used to allocate the returned column's device memory

Returns

New column with type matching the dictionary_column's keys

encode()

std::unique_ptr<column> cudf::dictionary::encode	(	column_view const &	column,
		data_type	indices_type = data_type{type_id::UINT32},
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Construct a dictionary column by dictionary encoding an existing column.

The output column is a DICTIONARY type with a keys column of non-null, unique values that are in a strict, total order. Meaning, keys[i] is _ordered before keys[i+1] for all i in [0,n-1) where n is the number of keys.

The output column has a child indices column that is of integer type and with the same size as the input column.

The null mask and null count are copied from the input column to the output column.

Exceptions

cudf::logic_error	if indices type is not an unsigned integer type
cudf::logic_error	if the column to encode is already a DICTIONARY type

c = [429, 111, 213, 111, 213, 429, 213]
d = encode(c)
d now has keys [111, 213, 429] and indices [2, 0, 1, 0, 1, 2, 1]

Parameters

column	The column to dictionary encode
indices_type	The integer type to use for the indices
stream	CUDA stream used for device memory operations and kernel launches
mr	Device memory resource used to allocate the returned column's device memory

Returns

Returns a dictionary column