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NumericToCategoricalEncoding Input Transform. #2907

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Motivation

This PR refers to #2879. It adds a new input transform that transforms a categorical degree of freedom encoded a an integer into some kind of vector based description. This could be for example a one-hot encoding, but also a descriptor encoding as it is often used in chemistry. It adds the possibility to use the alternating acqf optimizer also with surrogates that do not treat categoricals as integer based values. For example one could then also use a SAAS GP with the mixed alternating acqf optimizer and treat the categoricals under the hood as one-hots.

Have you read the Contributing Guidelines on pull requests?

Yes.

Test Plan

Unit tests, most of them are implemented (also to demonstrate the functionality), the ones which check the equality between transforms and correct behavior of transform on train etc. are still missing. My plan is to add them after a first feedback after a first review.

@facebook-github-bot facebook-github-bot added the CLA Signed Do not delete this pull request or issue due to inactivity. label Jul 1, 2025
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codecov bot commented Jul 1, 2025

Codecov Report

Attention: Patch coverage is 94.28571% with 2 lines in your changes missing coverage. Please review.

Project coverage is 99.98%. Comparing base (4e6079f) to head (69809b3).
Report is 2 commits behind head on main.

Files with missing lines Patch % Lines
botorch/models/transforms/input.py 94.28% 2 Missing ⚠️
Additional details and impacted files
@@             Coverage Diff             @@
##              main    #2907      +/-   ##
===========================================
- Coverage   100.00%   99.98%   -0.02%     
===========================================
  Files          212      212              
  Lines        19778    19813      +35     
===========================================
+ Hits         19778    19811      +33     
- Misses           0        2       +2     

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@jduerholt
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@saitcakmak @Balandat any thoughts on this? It would be totally fine for me, if you say that you do not see this functionality directly in botorch. Then I would integrate it into our codebase, which is also totally fine ;)

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The implementation seems reasonable to me. I'd be curious to see a concrete example using this end-to-end, including fitting a model and optimizing the acquisition function.

Similar to @saitcakmak , I would also be curious about how this compares against using a kernel that may work on the categoricals directly.

A `batch_shape x n x d'`-dim tensor of where the integer encoded
categoricals are transformed to a vector representation.
"""
if len(self.categorical_features) > 0:
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Since the whole transform would be a nullop if no categorical_features is provided, should you instead just not allow this and error out? Or do you want to be able to apply the transform universally even if there aren't any categorical features?

Comment on lines +1629 to +1631
"""Transform categorical parameters from an integer representation
to a vector based representation like one-hot encoding or a descriptor
encoding.
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Would be good to have a description of how the columns in the output of the transform are organized. Ideally there would be a concrete example in the docstring.

},
)

torch.manual_seed(randint(0, 1000))
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This seems to defy the point of locking the seed?

cont = torch.rand(3, 2, dtype=dtype, device=self.device)

X_numeric = torch.cat(
[cat_numeric.view(-1, 1).to(dtype=dtype, device=self.device), cont],
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No need for the .to(), can do that directly above: cat_numeric = torch.randint(0, 3, (3,), device=self.device, dtype=dtype)


Args:
dim: The dimension of the numerically encoded input.
categorical_features: A dictionary mapping the index of each
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this arg name could be more descriptive, e.g. numeric_cardinality or sth like that

@@ -1625,6 +1625,122 @@ def _expanded_perturbations(self, X: Tensor) -> Tensor:
return p.transpose(-3, -2) # p is batch_shape x n_p x n x d


class NumericToCategoricalEncoding(InputTransform):
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wait, should this not be CategoricalToNumeric?

Comment on lines +1288 to +1289
cat_numeric1.view(-1, 1).to(dtype=dtype, device=self.device),
cat_numeric2.view(-1, 1).to(dtype=dtype, device=self.device),
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same comment as above about to()

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3 participants