Demultiplexer

class torchdata.datapipes.iter.Demultiplexer(datapipe: IterDataPipe, num_instances: int, classifier_fn: Callable[[T_co], Optional[int]], drop_none: bool = False, buffer_size: int = 1000)

Splits the input DataPipe into multiple child DataPipes, using the given classification function (functional name: demux). A list of the child DataPipes is returned from this operation.

Parameters:

• datapipe – Iterable DataPipe being filtered

• num_instances – number of instances of the DataPipe to create

• classifier_fn – a function that maps values to an integer within the range [0, num_instances - 1] or None

• drop_none – defaults to False, if True, the function will skip over elements classified as None

• buffer_size – this defines the maximum number of inputs that the buffer can hold across all child DataPipes while waiting for their values to be yielded. Defaults to 1000. Use -1 for the unlimited buffer.

Examples

>>> # xdoctest: +REQUIRES(module:torchdata)
>>> from torchdata.datapipes.iter import IterableWrapper
>>> def odd_or_even(n):
...     return n % 2
>>> source_dp = IterableWrapper(range(5))
>>> dp1, dp2 = source_dp.demux(num_instances=2, classifier_fn=odd_or_even)
>>> list(dp1)
[0, 2, 4]
>>> list(dp2)
[1, 3]
>>> # It can also filter out any element that gets `None` from the `classifier_fn`
>>> def odd_or_even_no_zero(n):
...     return n % 2 if n != 0 else None
>>> dp1, dp2 = source_dp.demux(num_instances=2, classifier_fn=odd_or_even_no_zero, drop_none=True)
>>> list(dp1)
[2, 4]
>>> list(dp2)
[1, 3]