model_fit: Model Fit Objects

In parsnip: A Common API to Modeling and Analysis Functions

Model Fit Objects

Description

Model fits are trained model specifications that are ready to predict on new data. Model fits have class model_fit and, usually, a subclass referring to the engine used to fit the model.

Details

An object with class "model_fit" is a container for information about a model that has been fit to the data.

The main elements of the object are:

• lvl: A vector of factor levels when the outcome is a factor. This is NULL when the outcome is not a factor vector.

• spec: A model_spec object.

• fit: The object produced by the fitting function.

• preproc: This contains any data-specific information required to process new a sample point for prediction. For example, if the underlying model function requires arguments x and y and the user passed a formula to fit, the preproc object would contain items such as the terms object and so on. When no information is required, this is NA.

As discussed in the documentation for model_spec, the original arguments to the specification are saved as quosures. These are evaluated for the model_fit object prior to fitting. If the resulting model object prints its call, any user-defined options are shown in the call preceded by a tilde (see the example below). This is a result of the use of quosures in the specification.

This class and structure is the basis for how parsnip stores model objects after seeing the data and applying a model.

Examples

# Keep the `x` matrix if the data are not too big.
spec_obj <-
  linear_reg() |>
  set_engine("lm", x = ifelse(.obs() < 500, TRUE, FALSE))
spec_obj

fit_obj <- fit(spec_obj, mpg ~ ., data = mtcars)
fit_obj

nrow(fit_obj$fit$x)

parsnip documentation built on June 8, 2025, 12:10 p.m.