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Lambda transform should allow type conversion based on user-defined function #6379

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surajpaib opened this issue Apr 17, 2023 · 1 comment · Fixed by #6385
Closed

Lambda transform should allow type conversion based on user-defined function #6379

surajpaib opened this issue Apr 17, 2023 · 1 comment · Fixed by #6385

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@surajpaib
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surajpaib commented Apr 17, 2023

Is your feature request related to a problem? Please describe.
In the current implementation of Lambda transform, it always forces a conversion to MetaTensor when the output type is a numpy.ndarray or torch.Tensor and metadata tracking is enabled (default). This behavior may not be suitable for every use case, as it can lead to unnecessary conversions in certain scenarios.

In my current use case, my last transform attempts to convert from MetaTensor to Tensor so that I can use it for DDP with SyncBatchNorm #5198

I'd expect it to convert to whatever format is specified in the lambda function by the user.

Describe the solution you'd like
Allow the Lambda transform to return the initial output type without forcing a conversion to MetaTensor. This could be achieved by introducing an optional parameter (e.g., track_meta: bool = True) in the constructor and modifying the code accordingly. This parameter seems to already exist for other functions like convert_to_tensor

Describe alternatives you've considered
I now use torchvision.transforms.Lambda as a replacement.

@surajpaib
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Happy to make a PR for this as well!

wyli pushed a commit that referenced this issue Apr 18, 2023
Fixes #6379 

### Description
`track_meta` flag added to `Lambda` and derived transforms to allow type
conversion to `np.ndarray` and `torch.Tensor` based on user-defined
function

### Types of changes
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [x] Non-breaking change (fix or new feature that would not break
existing functionality).
- [ ] Breaking change (fix or new feature that would cause existing
functionality to change).
- [x] New tests added to cover the changes.
- [ ] Integration tests passed locally by running `./runtests.sh -f -u
--net --coverage`.
- [ ] Quick tests passed locally by running `./runtests.sh --quick
--unittests --disttests`.
- [x] In-line docstrings updated.
- [ ] Documentation updated, tested `make html` command in the `docs/`
folder.

Signed-off-by: Suraj Pai <bspai@bwh.harvard.edu>
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