numcodecs_bitmap_index

numcodecs_bitmap_index

BitmapIndexCodec for the numcodecs buffer compression API.

Modules:

  • typing –

    Commonly used type variables.

Classes:

  • BitmapIndexCodec –

    Codec that uses bitmaps to encode the most frequent bitpatterns in the data

BitmapIndexCodec 

BitmapIndexCodec(
    *,
    max_bitmaps: None | int = None,
    cost_factor: float = 1,
)

Bases: Codec

Codec that uses bitmaps to encode the most frequent bitpatterns in the data and encodes any remaining values as-is.

A simple heuristic is used to only encode bitpatterns with bitmaps where the direct savings outweigh the costs. The codec can be configured to bound the number of bitmaps or scale the cost.

Encoding produces a 1D array of unsigned integers with the same itemsize as the original data.

Parameters:
  • max_bitmaps (None | int, default: None ) –

    Maximum number of bitmaps to use.

  • cost_factor (float, default: 1 ) –

    Factor for the cost of a bitmap. Use >1 if bitmaps compress worse than the original data, or <1 if they compress better.

Methods:

  • encode –

    Encode the data in buf by replacing the most frequent bitpatterns

  • decode –

    Decode the data in buf.

  • get_config –

    Returns the configuration of the codec.

codec_id class-attribute instance-attribute 

codec_id: str = 'bitmap-index'

encode 

encode(
    buf: ndarray[S, dtype[T]],
) -> ndarray[tuple[int], dtype[U]]

Encode the data in buf by replacing the most frequent bitpatterns with bitmaps.

Parameters:
Returns:

decode 

decode(
    buf: ndarray[tuple[int], dtype[U]],
    out: None | ndarray[S, dtype[T]] = None,
) -> ndarray[S, dtype[T]]

Decode the data in buf.

Parameters:
  • buf (ndarray[tuple[int], dtype[U]]) –

    Encoded 1D array with an unsigned integer dtype.

  • out (None | ndarray[S, dtype[T]], default: None ) –

    Writeable array to store the decoded data.
Returns:

get_config 

get_config() -> dict

Returns the configuration of the codec.

numcodecs.registry.get_codec(config) can be used to reconstruct this codec from the returned config.

Returns:
  • config( dict ) –

    Configuration of the codec.