NotImplemented error when using a OneHotEncoder: {NOT_IMPLEMENTED : Could not find an implementation for Reshape(19) node with name 'Reshape'}

[davalle99]

I get the following error when using the OneHotEncoder of the sklearn library.
NotImplemented: [ONNXRuntimeError] : 9 : NOT_IMPLEMENTED : Could not find an implementation for Reshape(19) node with name 'Reshape'

As you can see in the code below, the model is really simple:

import pandas as pd
import numpy as np
from sklearn.pipeline import Pipeline
from sklearn.preprocessing import RobustScaler, OneHotEncoder
from sklearn.compose import ColumnTransformer
from sklearn.neural_network import MLPRegressor
import skl2onnx
from skl2onnx import convert_sklearn
from skl2onnx.algebra.type_helper import guess_initial_types
import onnxruntime as rt

X=pd.DataFrame({"A":[1,2,3], "B":["dog", "cat", "dog"], "C":["blue", "red", "green"]})
y=np.array([0,1,42])

preprocessor = ColumnTransformer(
    transformers=[
        ("num", RobustScaler(), ["A"]),
        ("cat", OneHotEncoder(), ["B", "C"]),
    ]
)  

pipeline = Pipeline([
            ('Preprocessing', preprocessor),
            ('Estimator', MLPRegressor(
                hidden_layer_sizes=[10],
                max_iter=2))
        ])

pipeline.fit(X,y)

initial_types = guess_initial_types(X=X, initial_types=None)
onx = convert_sklearn(pipeline, initial_types=initial_types)
with open("./example.onnx", "wb") as f:
    f.write(onx.SerializeToString())

sess = rt.InferenceSession("example.onnx", providers=rt.get_available_providers())

Traceback:

NotImplemented                            Traceback (most recent call last)
Cell In[5], line 36
     33 with open("./example.onnx", "wb") as f:
     34     f.write(onx.SerializeToString())
---> 36 sess = rt.InferenceSession("example.onnx", providers=rt.get_available_providers())

File /anaconda/envs/azureml_py310_sdkv2/lib/python3.10/site-packages/onnxruntime/capi/onnxruntime_inference_collection.py:383, in InferenceSession.__init__(self, path_or_bytes, sess_options, providers, provider_options, **kwargs)
    380 disabled_optimizers = kwargs["disabled_optimizers"] if "disabled_optimizers" in kwargs else None
    382 try:
--> 383     self._create_inference_session(providers, provider_options, disabled_optimizers)
    384 except (ValueError, RuntimeError) as e:
    385     if self._enable_fallback:

File /anaconda/envs/azureml_py310_sdkv2/lib/python3.10/site-packages/onnxruntime/capi/onnxruntime_inference_collection.py:435, in InferenceSession._create_inference_session(self, providers, provider_options, disabled_optimizers)
    432     disabled_optimizers = set(disabled_optimizers)
    434 # initialize the C++ InferenceSession
--> 435 sess.initialize_session(providers, provider_options, disabled_optimizers)
    437 self._sess = sess
    438 self._sess_options = self._sess.session_options

NotImplemented: [ONNXRuntimeError] : 9 : NOT_IMPLEMENTED : Could not find an implementation for Reshape(19) node with name 'Reshape'