TensorDictBase.apply#

TensorDictBase.apply(fn: Callable, *others: T, batch_size: Sequence[int] | None = None, device: device | None = NO_DEFAULT, names: Sequence[str] | None = NO_DEFAULT, inplace: bool = False, default: Any = NO_DEFAULT, filter_empty: bool | None = None, propagate_lock: bool = False, call_on_nested: bool = False, out: TensorDictBase | None = None, **constructor_kwargs) → Self | None#

Applies a callable to all values stored in the tensordict and sets them in a new tensordict.

The callable signature must be Callable[Tuple[Tensor, ...], Tensor | TensorDictBase | None].

Parameters:

fn (Callable) – function to be applied to the tensors in the tensordict.
*others (TensorDictBase instances, optional) – if provided, these tensordict instances should have a structure matching the one of self. The fn argument should receive as many unnamed inputs as the number of tensordicts, including self. If other tensordicts have missing entries, a default value can be passed through the default keyword argument.

Keyword Arguments:

batch_size (sequence of int, optional) – if provided, the resulting TensorDict will have the desired batch_size. The batch_size argument should match the batch_size after the transformation. This is a keyword only argument. With a batch_size, the call is treated as a shape operation: fn is not called on UnbatchedTensor entries, which keep their data and take the new batch size.
device (device, optional) – the resulting device, if any.
names (list of str, optional) – the new dimension names, in case the batch_size is modified.
inplace (bool, optional) – if True, the results are written into the existing leaves of self (as set_() does), and self is returned. Defaults to False. See In-place operations.
default (Any, optional) – default value for missing entries in the other tensordicts. If not provided, missing entries will raise a KeyError.
filter_empty (bool, optional) – if True, empty tensordicts will be filtered out. This also comes with a lower computational cost as empty data structures won’t be created and destroyed. Non-tensor data is considered as a leaf and thereby will be kept in the tensordict even if left untouched by the function. If False, empty tensordicts are kept. Defaults to None, which behaves like True (tensordicts left empty by fn are filtered out, and None is returned if fn returns no value at all) except that tensordicts that were already empty are kept.
propagate_lock (bool, optional) – if True, a locked tensordict will produce another locked tensordict. Defaults to False.

call_on_nested (bool, optional) –

if True, the function will be called on first-level tensors and containers (TensorDict or tensorclass). In this scenario, func is responsible of propagating its calls to nested levels. This allows a fine-grained behaviour when propagating the calls to nested tensordicts. If False, the function will only be called on leaves, and apply will take care of dispatching the function to all leaves.

>>> from tensordict import TensorDict, is_tensor_collection
>>> td = TensorDict({"a": {"b": [0.0, 1.0]}, "c": [1.0, 2.0]})
>>> def mean_tensor_only(val):
...     if is_tensor_collection(val):
...         raise RuntimeError("Unexpected!")
...     return val.mean()
>>> td_mean = td.apply(mean_tensor_only)
>>> def mean_any(val):
...     if is_tensor_collection(val):
...         # Recurse
...         return val.apply(mean_any, call_on_nested=True)
...     return val.mean()
>>> td_mean = td.apply(mean_any, call_on_nested=True)

out (TensorDictBase, optional) –
a tensordict where to write the results. This can be used to avoid creating a new tensordict:
```
>>> td = TensorDict({"a": 0})
>>> _ = td.apply(lambda x: x+1, out=td)
>>> assert (td==1).all()
```
Warning

If the operation executed on the tensordict requires multiple keys to be accessed for a single computation, providing an out argument equal to self can cause the operation to provide silently wrong results. For instance:
```
>>> td = TensorDict({"a": 1, "b": 1})
>>> td.apply(lambda x: x+td["a"])["b"] # Right!
tensor(2)
>>> td.apply(lambda x: x+td["a"], out=td)["b"] # Wrong!
tensor(3)
```
**constructor_kwargs – additional keyword arguments to be passed to the TensorDict constructor.

Returns:

a new tensordict with the transformed tensors, or self if inplace=True. None if fn returns None for every leaf and filter_empty is not False.

The result has the same type as self for TensorDict, LazyStackedTensorDict and tensorclasses. Other types, for example PersistentTensorDict or a memory-mapped tensordict, give a TensorDict that lives in memory.

A locked tensordict gives an unlocked result unless propagate_lock=True.

Examples

>>> import torch
>>> from tensordict import TensorDict
>>> td = TensorDict({
...     "a": -torch.ones(3),
...     "b": {"c": torch.ones(3)}},
...     batch_size=[3])
>>> td_1 = td.apply(lambda x: x+1)
>>> assert (td_1["a"] == 0).all()
>>> assert (td_1["b", "c"] == 2).all()
>>> td_2 = td.apply(lambda x, y: x+y, td)
>>> assert (td_2["a"] == -2).all()
>>> assert (td_2["b", "c"] == 2).all()

Note

If None is returned by the function, the entry is ignored. This can be used to filter the data in the tensordict:

>>> td = TensorDict({"1": 1, "2": 2, "b": {"2": 2, "1": 1}}, [])
>>> def filter(tensor):
...     if tensor == 1:
...         return tensor
>>> td.apply(filter)
TensorDict(
    fields={
        1: Tensor(shape=torch.Size([]), device=cpu, dtype=torch.int64, is_shared=False),
        b: TensorDict(
            fields={
                1: Tensor(shape=torch.Size([]), device=cpu, dtype=torch.int64, is_shared=False)},
            batch_size=torch.Size([]),
            device=None,
            is_shared=False)},
    batch_size=torch.Size([]),
    device=None,
    is_shared=False)

Every tensordict class and every tensorclass has this method. For the other methods, see Methods by task.

Tutorials that use `apply`#

Building tensordicts from streams

TensorDictBase.apply#

Tutorials that use `apply`#

Docs

Tutorials

Resources

TensorDictBase.apply#

Tutorials that use apply#

Docs

Tutorials

Resources

Tutorials that use `apply`#