sk-learn Regression Model to ONNX Outside Wallaroo

How to convert sk-learn Regression ML models into the ONNX format.

This tutorial and the assets can be downloaded as part of the Wallaroo Tutorials repository.

How to Convert sk-learn Regression Model to ONNX

The following tutorial is a brief example of how to convert a scikit-learn (aka sk-learn) regression ML model to the ONNX.

This tutorial assumes that you have a Wallaroo instance and are running this Notebook from the Wallaroo Jupyter Hub service.

This tutorial provides the following:

  • demand_curve.pickle: a demand curve trained sk-learn model. Once this file is converted to ONNX format, it can be used as part of the Demand Curve Pipeline Tutorial.

    This model contains 3 columns: UnitPrice, cust_known, and UnitPriceXcust_known.

Conversion Process


The first step is to import our libraries we will be using.

# Used to load the sk-learn model
import pickle

# Used for the conversion process
import onnx, skl2onnx, onnxmltools
from skl2onnx.common.data_types import FloatTensorType
from skl2onnx.common.data_types import DoubleTensorType

Next let’s define our model_to_onnx method for converting a sk-learn model to ONNX. This has the following inputs:

  • model: The sk-learn model we’re converting.
  • cols: The number of inputs the model expects
  • input_type: Determines how to manage float values, which can either be DoubleTensorType or FloatTensorType.
# convert model to ONNX

def model_to_onnx(model, cols, *, input_type='Double'):
    # How to manage float values
    if input_type=='Double':
    elif input_type=='Float':
        raise ValueError("bad input type")
    initial_type=[(f'{input_type_lower}_input', tensor_type([None, tensor_size]))]
    return onnx_model

With our method defined, now it’s time to convert. Let’s load our sk-learn model and save it into the variable sklearn_model.

# pickle the model, so I can try the Wallaroo converter on it

sklearn_model = pickle.load(open('./demand_curve.pickle', 'rb'))
/opt/homebrew/anaconda3/envs/arrowtests/lib/python3.8/site-packages/sklearn/ UserWarning: Trying to unpickle estimator LinearRegression from version 0.24.2 when using version 1.1.2. This might lead to breaking code or invalid results. Use at your own risk. For more info please refer to:

Now we’ll convert our sklearn-model into the variable onnx_model using our model_to_onnx method. Recall that our sklearn-model has 3 columns.

onnx_model_converted = model_to_onnx(sklearn_model, 3)

Now we can save our model to a onnx file.

onnx.save_model(onnx_model_converted, "demand_curve.onnx")