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from typing import Callable, List, Tuple, TypeVar, cast
from ..config import registry
from ..model import Model
from ..types import ArrayXd, ListXd, Ragged
InT = TypeVar("InT", bound=ListXd)
OutT = Ragged
@registry.layers("list2ragged.v1")
def list2ragged() -> Model[InT, OutT]:
"""Transform sequences to ragged arrays if necessary and return the ragged
array. If sequences are already ragged, do nothing. A ragged array is a
tuple (data, lengths), where data is the concatenated data.
"""
return Model("list2ragged", forward)
def forward(model: Model[InT, OutT], Xs: InT, is_train: bool) -> Tuple[OutT, Callable]:
def backprop(dYr: OutT) -> InT:
return cast(InT, model.ops.unflatten(dYr.data, dYr.lengths))
lengths = model.ops.asarray1i([len(x) for x in Xs])
return Ragged(model.ops.flatten(Xs), lengths), backprop
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