# Tidymodels Workflow with Functional Keras Models (Multi-Input)

## Introduction

This vignette demonstrates a complete `tidymodels` workflow for a regression task using a Keras functional model defined with `kerasnip`. We will use the Ames Housing dataset to predict house prices. A key feature of this example is the use of a multi-input Keras model, where numerical and categorical features are processed through separate input branches.

`kerasnip` allows you to define complex Keras architectures, including those with multiple inputs, and integrate them seamlessly into the `tidymodels` ecosystem for robust modeling and tuning.

## Setup

First, we load the necessary packages.

    library(kerasnip)
    library(tidymodels)
    #> ── Attaching packages ───────────────── tidymodels 1.5.0 ──
    #> ✔ broom        1.0.13     ✔ recipes      1.3.3
    #> ✔ dials        1.4.4      ✔ rsample      1.3.2
    #> ✔ dplyr        1.2.1      ✔ tailor       0.1.0
    #> ✔ ggplot2      4.0.3      ✔ tidyr        1.3.2
    #> ✔ infer        1.1.0      ✔ tune         2.1.0
    #> ✔ modeldata    1.5.1      ✔ workflows    1.3.0
    #> ✔ parsnip      1.6.0      ✔ workflowsets 1.1.1
    #> ✔ purrr        1.2.2      ✔ yardstick    1.4.0
    #> ── Conflicts ──────────────────── tidymodels_conflicts() ──
    #> ✖ purrr::discard()         masks scales::discard()
    #> ✖ dplyr::filter()          masks stats::filter()
    #> ✖ parsnip::get_model_env() masks kerasnip::get_model_env()
    #> ✖ dplyr::lag()             masks stats::lag()
    #> ✖ recipes::step()          masks stats::step()
    library(keras3)
    #>
    #> Attaching package: 'keras3'
    #> The following object is masked from 'package:yardstick':
    #>
    #>     get_weights
    #> The following object is masked from 'package:infer':
    #>
    #>     generate
    library(dplyr) # For data manipulation
    library(ggplot2) # For plotting
    library(future) # For parallel processing
    #>
    #> Attaching package: 'future'
    #> The following object is masked from 'package:keras3':
    #>
    #>     %<-%
    library(finetune) # For racing

## Data Preparation

We’ll use the Ames Housing dataset, which is available in the `modeldata` package. We will then split the data into training and testing sets.

    # Select relevant columns and remove rows with missing values
    ames_df <- ames |>
      select(
        Sale_Price,
        Gr_Liv_Area,
        Year_Built,
        Neighborhood,
        Bldg_Type,
        Overall_Cond,
        Total_Bsmt_SF,
        contains("SF")
      ) |>
      na.omit()

    # Split data into training and testing sets
    set.seed(123)
    ames_split <- initial_split(ames_df, prop = 0.8, strata = Sale_Price)
    ames_train <- training(ames_split)
    ames_test <- testing(ames_split)

    # Create cross-validation folds for tuning
    ames_folds <- vfold_cv(ames_train, v = 5, strata = Sale_Price)

## Recipe for Preprocessing

We will create a `recipes` object to preprocess our data. This recipe will: * Predict `Sale_Price` using all other variables. * Normalize all numerical predictors. * Create dummy variables for categorical predictors. * Collapse each group of predictors into a single matrix column using `step_collapse()`.

This final step is crucial for the multi-input Keras model, as the `kerasnip` functional API expects a list of matrices for multiple inputs, where each matrix corresponds to a distinct input layer.

    ames_recipe <- recipe(Sale_Price ~ ., data = ames_train) |>
      step_normalize(all_numeric_predictors()) |>
      step_collapse(all_numeric_predictors(), new_col = "numerical_input") |>
      step_dummy(Neighborhood) |>
      step_collapse(starts_with("Neighborhood"), new_col = "neighborhood_input") |>
      step_dummy(Bldg_Type) |>
      step_collapse(starts_with("Bldg_Type"), new_col = "bldg_input") |>
      step_dummy(Overall_Cond) |>
      step_collapse(starts_with("Overall_Cond"), new_col = "condition_input")

## Define Keras Functional Model with `kerasnip`

Now, we define our Keras functional model using `kerasnip`’s layer blocks. This model will have four distinct input layers: one for numerical features and three for categorical features. These branches will be processed separately and then concatenated before the final output layer.

    # Define layer blocks for multi-input functional model

    # Input blocks for numerical and categorical features
    input_numerical <- function(input_shape) {
      layer_input(shape = input_shape, name = "numerical_input")
    }

    input_neighborhood <- function(input_shape) {
      layer_input(shape = input_shape, name = "neighborhood_input")
    }

    input_bldg <- function(input_shape) {
      layer_input(shape = input_shape, name = "bldg_input")
    }

    input_condition <- function(input_shape) {
      layer_input(shape = input_shape, name = "condition_input")
    }

    # Processing blocks for each input type
    dense_numerical <- function(tensor, units = 32, activation = "relu") {
      tensor |>
        layer_dense(units = units, activation = activation)
    }

    dense_categorical <- function(tensor, units = 16, activation = "relu") {
      tensor |>
        layer_dense(units = units, activation = activation)
    }

    # Concatenation block
    concatenate_features <- function(numeric, neighborhood, bldg, condition) {
      layer_concatenate(list(numeric, neighborhood, bldg, condition))
    }

    # Output block for regression
    output_regression <- function(tensor) {
      layer_dense(tensor, units = 1, name = "output")
    }

    # Create the kerasnip model specification function
    create_keras_functional_spec(
      model_name = "ames_functional_mlp",
      layer_blocks = list(
        numerical_input = input_numerical,
        neighborhood_input = input_neighborhood,
        bldg_input = input_bldg,
        condition_input = input_condition,
        processed_numerical = inp_spec(dense_numerical, "numerical_input"),
        processed_neighborhood = inp_spec(dense_categorical, "neighborhood_input"),
        processed_bldg = inp_spec(dense_categorical, "bldg_input"),
        processed_condition = inp_spec(dense_categorical, "condition_input"),
        combined_features = inp_spec(
          concatenate_features,
          c(
            numeric = "processed_numerical",
            neighborhood = "processed_neighborhood",
            bldg = "processed_bldg",
            condition = "processed_condition"
          )
        ),
        output = inp_spec(output_regression, "combined_features")
      ),
      mode = "regression"
    )

## Model Specification

We’ll define our `ames_functional_mlp` model specification and set some hyperparameters to `tune()`. Note how the arguments are prefixed with their corresponding block names (e.g., `processed_numerical_units`).

    # Define the tunable model specification
    functional_mlp_spec <- ames_functional_mlp(
      # Tunable parameters for numerical branch
      processed_numerical_units = tune(),
      # Tunable parameters for categorical branch
      processed_neighborhood_units = tune(),
      processed_bldg_units = tune(),
      processed_condition_units = tune(),
      # Fixed compilation and fitting parameters
      compile_loss = "mean_squared_error",
      compile_optimizer = "adam",
      compile_metrics = c("mean_absolute_error"),
      fit_epochs = 50,
      fit_batch_size = 32,
      fit_validation_split = 0.2,
      fit_callbacks = list(
        callback_early_stopping(monitor = "val_loss", patience = 5)
      )
    ) |>
      set_engine("keras")

    print(functional_mlp_spec)
    #> ames functional mlp Model Specification (regression)
    #>
    #> Main Arguments:
    #>   num_numerical_input = structure(list(), class = "rlang_zap")
    #>   num_neighborhood_input = structure(list(), class = "rlang_zap")
    #>   num_bldg_input = structure(list(), class = "rlang_zap")
    #>   num_condition_input = structure(list(), class = "rlang_zap")
    #>   num_processed_numerical = structure(list(), class = "rlang_zap")
    #>   num_processed_neighborhood = structure(list(), class = "rlang_zap")
    #>   num_processed_bldg = structure(list(), class = "rlang_zap")
    #>   num_processed_condition = structure(list(), class = "rlang_zap")
    #>   num_combined_features = structure(list(), class = "rlang_zap")
    #>   num_output = structure(list(), class = "rlang_zap")
    #>   processed_numerical_units = tune()
    #>   processed_numerical_activation = structure(list(), class = "rlang_zap")
    #>   processed_neighborhood_units = tune()
    #>   processed_neighborhood_activation = structure(list(), class = "rlang_zap")
    #>   processed_bldg_units = tune()
    #>   processed_bldg_activation = structure(list(), class = "rlang_zap")
    #>   processed_condition_units = tune()
    #>   processed_condition_activation = structure(list(), class = "rlang_zap")
    #>   learn_rate = structure(list(), class = "rlang_zap")
    #>   fit_batch_size = 32
    #>   fit_epochs = 50
    #>   fit_callbacks = list(callback_early_stopping(monitor = "val_loss", patience = 5))
    #>   fit_validation_split = 0.2
    #>   fit_validation_data = structure(list(), class = "rlang_zap")
    #>   fit_shuffle = structure(list(), class = "rlang_zap")
    #>   fit_class_weight = structure(list(), class = "rlang_zap")
    #>   fit_sample_weight = structure(list(), class = "rlang_zap")
    #>   fit_initial_epoch = structure(list(), class = "rlang_zap")
    #>   fit_steps_per_epoch = structure(list(), class = "rlang_zap")
    #>   fit_validation_steps = structure(list(), class = "rlang_zap")
    #>   fit_validation_batch_size = structure(list(), class = "rlang_zap")
    #>   fit_validation_freq = structure(list(), class = "rlang_zap")
    #>   fit_verbose = structure(list(), class = "rlang_zap")
    #>   fit_view_metrics = structure(list(), class = "rlang_zap")
    #>   compile_optimizer = adam
    #>   compile_loss = mean_squared_error
    #>   compile_metrics = c("mean_absolute_error")
    #>   compile_loss_weights = structure(list(), class = "rlang_zap")
    #>   compile_weighted_metrics = structure(list(), class = "rlang_zap")
    #>   compile_run_eagerly = structure(list(), class = "rlang_zap")
    #>   compile_steps_per_execution = structure(list(), class = "rlang_zap")
    #>   compile_jit_compile = structure(list(), class = "rlang_zap")
    #>   compile_auto_scale_loss = structure(list(), class = "rlang_zap")
    #>
    #> Computational engine: keras

## Create Workflow

A `workflow` combines the recipe and the model specification.

    ames_wf <- workflow() |>
      add_recipe(ames_recipe) |>
      add_model(functional_mlp_spec)

    print(ames_wf)
    #> ══ Workflow ═══════════════════════════════════════════════
    #> Preprocessor: Recipe
    #> Model: ames_functional_mlp()
    #>
    #> ── Preprocessor ───────────────────────────────────────────
    #> 8 Recipe Steps
    #>
    #> • step_normalize()
    #> • step_collapse()
    #> • step_dummy()
    #> • step_collapse()
    #> • step_dummy()
    #> • step_collapse()
    #> • step_dummy()
    #> • step_collapse()
    #>
    #> ── Model ──────────────────────────────────────────────────
    #> ames functional mlp Model Specification (regression)
    #>
    #> Main Arguments:
    #>   num_numerical_input = structure(list(), class = "rlang_zap")
    #>   num_neighborhood_input = structure(list(), class = "rlang_zap")
    #>   num_bldg_input = structure(list(), class = "rlang_zap")
    #>   num_condition_input = structure(list(), class = "rlang_zap")
    #>   num_processed_numerical = structure(list(), class = "rlang_zap")
    #>   num_processed_neighborhood = structure(list(), class = "rlang_zap")
    #>   num_processed_bldg = structure(list(), class = "rlang_zap")
    #>   num_processed_condition = structure(list(), class = "rlang_zap")
    #>   num_combined_features = structure(list(), class = "rlang_zap")
    #>   num_output = structure(list(), class = "rlang_zap")
    #>   processed_numerical_units = tune()
    #>   processed_numerical_activation = structure(list(), class = "rlang_zap")
    #>   processed_neighborhood_units = tune()
    #>   processed_neighborhood_activation = structure(list(), class = "rlang_zap")
    #>   processed_bldg_units = tune()
    #>   processed_bldg_activation = structure(list(), class = "rlang_zap")
    #>   processed_condition_units = tune()
    #>   processed_condition_activation = structure(list(), class = "rlang_zap")
    #>   learn_rate = structure(list(), class = "rlang_zap")
    #>   fit_batch_size = 32
    #>   fit_epochs = 50
    #>   fit_callbacks = list(callback_early_stopping(monitor = "val_loss", patience = 5))
    #>   fit_validation_split = 0.2
    #>   fit_validation_data = structure(list(), class = "rlang_zap")
    #>   fit_shuffle = structure(list(), class = "rlang_zap")
    #>   fit_class_weight = structure(list(), class = "rlang_zap")
    #>   fit_sample_weight = structure(list(), class = "rlang_zap")
    #>   fit_initial_epoch = structure(list(), class = "rlang_zap")
    #>   fit_steps_per_epoch = structure(list(), class = "rlang_zap")
    #>   fit_validation_steps = structure(list(), class = "rlang_zap")
    #>   fit_validation_batch_size = structure(list(), class = "rlang_zap")
    #>   fit_validation_freq = structure(list(), class = "rlang_zap")
    #>   fit_verbose = structure(list(), class = "rlang_zap")
    #>   fit_view_metrics = structure(list(), class = "rlang_zap")
    #>   compile_optimizer = adam
    #>   compile_loss = mean_squared_error
    #>   compile_metrics = c("mean_absolute_error")
    #>   compile_loss_weights = structure(list(), class = "rlang_zap")
    #>   compile_weighted_metrics = structure(list(), class = "rlang_zap")
    #>   compile_run_eagerly = structure(list(), class = "rlang_zap")
    #>   compile_steps_per_execution = structure(list(), class = "rlang_zap")
    #>   compile_jit_compile = structure(list(), class = "rlang_zap")
    #>   compile_auto_scale_loss = structure(list(), class = "rlang_zap")
    #>
    #> Computational engine: keras

## Define Tuning Grid

We will create a regular grid for our hyperparameters.

    # Define the tuning grid
    params <- extract_parameter_set_dials(ames_wf) |>
      update(
        processed_numerical_units = hidden_units(range = c(32, 128)),
        processed_neighborhood_units = hidden_units(range = c(16, 64)),
        processed_bldg_units = hidden_units(range = c(16, 64)),
        processed_condition_units = hidden_units(range = c(16, 64))
      )
    functional_mlp_grid <- grid_regular(params, levels = 3)

    print(functional_mlp_grid)
    #> # A tibble: 81 × 4
    #>    processed_numerical_units processed_neighborhood_units processed_bldg_units processed_condition_units
    #>                        <int>                        <int>                <int>                     <int>
    #>  1                        32                           16                   16                        16
    #>  2                        80                           16                   16                        16
    #>  3                       128                           16                   16                        16
    #>  4                        32                           40                   16                        16
    #>  5                        80                           40                   16                        16
    #>  6                       128                           40                   16                        16
    #>  7                        32                           64                   16                        16
    #>  8                        80                           64                   16                        16
    #>  9                       128                           64                   16                        16
    #> 10                        32                           16                   40                        16
    #> # ℹ 71 more rows

## Tune Model

Now, we’ll use `tune_race_anova()` to perform cross-validation and find the best hyperparameters.

    # Note: Parallel processing with `plan(multisession)` is currently not working
    # with Keras models due to backend conflicts

    set.seed(123)
    ames_tune_results <- tune_race_anova(
      ames_wf,
      resamples = ames_folds,
      grid = functional_mlp_grid,
      metrics = metric_set(rmse, mae, rsq),
      control = control_race(save_pred = TRUE, save_workflow = TRUE)
    )

## Inspect Tuning Results

We can inspect the tuning results to see which hyperparameter combinations performed best.

    # Show the best performing models based on RMSE
    show_best(ames_tune_results, metric = "rmse", n = 5)
    #> # A tibble: 3 × 10
    #>   processed_numerical_units processed_neighborho…¹ processed_bldg_units processed_condition_…² .metric .estimator   mean
    #>                       <int>                  <int>                <int>                  <int> <chr>   <chr>       <dbl>
    #> 1                       128                     64                   40                     64 rmse    standard   54047.
    #> 2                       128                     64                   64                     64 rmse    standard   54150.
    #> 3                       128                     64                   16                     64 rmse    standard   54889.
    #> # ℹ abbreviated names: ¹​processed_neighborhood_units, ²​processed_condition_units
    #> # ℹ 3 more variables: n <int>, std_err <dbl>, .config <chr>

    # Autoplot the results
    # Currently does not work due to a label issue: autoplot(ames_tune_results)

    # Select the best hyperparameters
    best_functional_mlp_params <- select_best(ames_tune_results, metric = "rmse")
    print(best_functional_mlp_params)
    #> # A tibble: 1 × 5
    #>   processed_numerical_units processed_neighborhood_units processed_bldg_units processed_condition_units .config
    #>                       <int>                        <int>                <int>                     <int> <chr>
    #> 1                       128                           64                   40                        64 pre0_mod78_post0

## Finalize Workflow and Fit Model

Once we have the best hyperparameters, we finalize the workflow and fit the model on the entire training dataset.

    # Finalize the workflow with the best hyperparameters
    final_ames_wf <- finalize_workflow(ames_wf, best_functional_mlp_params)

    # Fit the final model on the full training data
    final_ames_fit <- fit(final_ames_wf, data = ames_train)
    #> 74/74 - 0s - 4ms/step

    print(final_ames_fit)
    #> ══ Workflow [trained] ═════════════════════════════════════
    #> Preprocessor: Recipe
    #> Model: ames_functional_mlp()
    #>
    #> ── Preprocessor ───────────────────────────────────────────
    #> 8 Recipe Steps
    #>
    #> • step_normalize()
    #> • step_collapse()
    #> • step_dummy()
    #> • step_collapse()
    #> • step_dummy()
    #> • step_collapse()
    #> • step_dummy()
    #> • step_collapse()
    #>
    #> ── Model ──────────────────────────────────────────────────
    #> $fit
    #> Model: "functional_517"
    #> ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
    #> ┃ Layer (type)                      ┃ Output Shape                 ┃           Param # ┃ Connected to                  ┃
    #> ┡━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┩
    #> │ numerical_input (InputLayer)      │ (None, 1, 10)                │                 0 │ -                             │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ neighborhood_input (InputLayer)   │ (None, 1, 28)                │                 0 │ -                             │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ bldg_input (InputLayer)           │ (None, 1, 4)                 │                 0 │ -                             │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ condition_input (InputLayer)      │ (None, 1, 9)                 │                 0 │ -                             │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ dense_1026 (Dense)                │ (None, 1, 128)               │             1,408 │ numerical_input[0][0]         │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ dense_1027 (Dense)                │ (None, 1, 64)                │             1,856 │ neighborhood_input[0][0]      │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ dense_1028 (Dense)                │ (None, 1, 40)                │               200 │ bldg_input[0][0]              │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ dense_1029 (Dense)                │ (None, 1, 64)                │               640 │ condition_input[0][0]         │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ concatenate_258 (Concatenate)     │ (None, 1, 296)               │                 0 │ dense_1026[0][0],             │
    #> │                                   │                              │                   │ dense_1027[0][0],             │
    #> │                                   │                              │                   │ dense_1028[0][0],             │
    #> │                                   │                              │                   │ dense_1029[0][0]              │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ output (Dense)                    │ (None, 1, 1)                 │               297 │ concatenate_258[0][0]         │
    #> └───────────────────────────────────┴──────────────────────────────┴───────────────────┴───────────────────────────────┘
    #>  Total params: 13,205 (51.59 KB)
    #>  Trainable params: 4,401 (17.19 KB)
    #>  Non-trainable params: 0 (0.00 B)
    #>  Optimizer params: 8,804 (34.39 KB)
    #>
    #> $keras_bytes
    #>     [1] 50 4b 03 04 14 00 00 00 00 00 00 00 21 00 8f d4 c0 4e 40 00 00 00 40 00 00 00 0d 00 00 00 6d 65 74 61 64 61 74
    #>    [38] 61 2e 6a 73 6f 6e 7b 22 6b 65 72 61 73 5f 76 65 72 73 69 6f 6e 22 3a 20 22 33 2e 31 35 2e 31 22 2c 20 22 64 61
    #>    [75] 74 65 5f 73 61 76 65 64 22 3a 20 22 32 30 32 36 2d 30 39 2d 30 33 40 31 38 3a 31 35 3a 31 30 22 7d 50 4b 03 04
    #>   [112] 14 00 00 00 00 00 00 00 21 00 70 ca d5 1d 1c 21 00 00 1c 21 00 00 0b 00 00 00 63 6f 6e 66 69 67 2e 6a 73 6f 6e
    #>   [149] 7b 22 6d 6f 64 75 6c 65 22 3a 20 22 6b 65 72 61 73 2e 73 72 63 2e 6d 6f 64 65 6c 73 2e 66 75 6e 63 74 69 6f 6e
    #>   [186] 61 6c 22 2c 20 22 63 6c 61 73 73 5f 6e 61 6d 65 22 3a 20 22 46 75 6e 63 74 69 6f 6e 61 6c 22 2c 20 22 63 6f 6e
    #>   [223] 66 69 67 22 3a 20 7b 22 6e 61 6d 65 22 3a 20 22 66 75 6e 63 74 69 6f 6e 61 6c 5f 35 31 37 22 2c 20 22 74 72 61
    #>   [260] 69 6e 61 62 6c 65 22 3a 20 74 72 75 65 2c 20 22 6c 61 79 65 72 73 22 3a 20 5b 7b 22 6d 6f 64 75 6c 65 22 3a 20
    #>   [297] 22 6b 65 72 61 73 2e 6c 61 79 65 72 73 22 2c 20 22 63 6c 61 73 73 5f 6e 61 6d 65 22 3a 20 22 49 6e 70 75 74 4c
    #>   [334] 61 79 65 72 22 2c 20 22 63 6f 6e 66 69 67 22 3a 20 7b 22 62 61 74 63 68 5f 73 68 61 70 65 22 3a 20 5b 6e 75 6c
    #>   [371] 6c 2c 20 31 2c 20 31 30 5d 2c 20 22 64 74 79 70 65 22 3a 20 22 66 6c 6f 61 74 33 32 22 2c 20 22 73 70 61 72 73
    #>   [408] 65 22 3a 20 66 61 6c 73 65 2c 20 22 72 61 67 67 65 64 22 3a 20 66 61 6c 73 65 2c 20 22 6e 61 6d 65 22 3a 20 22
    #>   [445] 6e 75 6d 65 72 69 63 61 6c 5f 69 6e 70 75 74 22 2c 20 22 6f 70 74 69 6f 6e 61 6c 22 3a 20 66 61 6c 73 65 7d 2c
    #>   [482] 20 22 72 65 67 69 73 74 65 72 65 64 5f 6e 61 6d 65 22 3a 20 6e 75 6c 6c 2c 20 22 6e 61 6d 65 22 3a 20 22 6e 75
    #>   [519] 6d 65 72 69 63 61 6c 5f 69 6e 70 75 74 22 2c 20 22 69 6e 62 6f 75 6e 64 5f 6e 6f 64 65 73 22 3a 20 5b 5d 7d 2c
    #>   [556] 20 7b 22 6d 6f 64 75 6c 65 22 3a 20 22 6b 65 72 61 73 2e 6c 61 79 65 72 73 22 2c 20 22 63 6c 61 73 73 5f 6e 61
    #>
    #> ...
    #> and 4359 more lines.

### Inspect Final Model

You can extract the underlying Keras model and its training history for further inspection.

    # Extract the Keras model summary
    final_ames_fit |>
      extract_fit_parsnip() |>
      extract_keras_model() |>
      summary()
    #> Model: "functional_517"
    #> ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
    #> ┃ Layer (type)                      ┃ Output Shape                 ┃           Param # ┃ Connected to                  ┃
    #> ┡━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┩
    #> │ numerical_input (InputLayer)      │ (None, 1, 10)                │                 0 │ -                             │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ neighborhood_input (InputLayer)   │ (None, 1, 28)                │                 0 │ -                             │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ bldg_input (InputLayer)           │ (None, 1, 4)                 │                 0 │ -                             │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ condition_input (InputLayer)      │ (None, 1, 9)                 │                 0 │ -                             │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ dense_1026 (Dense)                │ (None, 1, 128)               │             1,408 │ numerical_input[0][0]         │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ dense_1027 (Dense)                │ (None, 1, 64)                │             1,856 │ neighborhood_input[0][0]      │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ dense_1028 (Dense)                │ (None, 1, 40)                │               200 │ bldg_input[0][0]              │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ dense_1029 (Dense)                │ (None, 1, 64)                │               640 │ condition_input[0][0]         │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ concatenate_258 (Concatenate)     │ (None, 1, 296)               │                 0 │ dense_1026[0][0],             │
    #> │                                   │                              │                   │ dense_1027[0][0],             │
    #> │                                   │                              │                   │ dense_1028[0][0],             │
    #> │                                   │                              │                   │ dense_1029[0][0]              │
    #> ├───────────────────────────────────┼──────────────────────────────┼───────────────────┼───────────────────────────────┤
    #> │ output (Dense)                    │ (None, 1, 1)                 │               297 │ concatenate_258[0][0]         │
    #> └───────────────────────────────────┴──────────────────────────────┴───────────────────┴───────────────────────────────┘
    #>  Total params: 13,205 (51.59 KB)
    #>  Trainable params: 4,401 (17.19 KB)
    #>  Non-trainable params: 0 (0.00 B)
    #>  Optimizer params: 8,804 (34.39 KB)

    # Plot the Keras model
    final_ames_fit |>
      extract_fit_parsnip() |>
      extract_keras_model() |>
      plot(show_shapes = TRUE)

Model

    # Plot the training history
    final_ames_fit |>
      extract_fit_parsnip() |>
      extract_keras_history() |>
      plot()

plot of chunk inspect-final-keras-model-history

## Make Predictions and Evaluate

Finally, we will make predictions on the test set and evaluate the model’s performance.

    # Make predictions on the test set
    ames_test_pred <- predict(final_ames_fit, new_data = ames_test)
    #> 19/19 - 0s - 11ms/step

    # Combine predictions with actuals
    ames_results <- tibble::tibble(
      Sale_Price = ames_test$Sale_Price,
      .pred = ames_test_pred$.pred
    )

    print(head(ames_results))
    #> # A tibble: 6 × 2
    #>   Sale_Price   .pred
    #>        <int>   <dbl>
    #> 1     189900 193897.
    #> 2     195500 195599.
    #> 3     236500 234444.
    #> 4     212000 223605.
    #> 5     210000 244144.
    #> 6     142000 125377.

    # Evaluate performance using yardstick metrics
    metrics_results <- metric_set(
      rmse,
      mae,
      rsq
    )(
      ames_results,
      truth = Sale_Price,
      estimate = .pred
    )

    print(metrics_results)
    #> # A tibble: 3 × 3
    #>   .metric .estimator .estimate
    #>   <chr>   <chr>          <dbl>
    #> 1 rmse    standard   44555.
    #> 2 mae     standard   28009.
    #> 3 rsq     standard       0.766

## Saving and Reloading Your Model

`kerasnip` serializes the Keras model weights to bytes at fit time and stores them alongside the workflow object. This means plain `saveRDS()` / `readRDS()` works out of the box — the underlying Keras model is restored automatically the first time `predict()` is called on the reloaded object.

    # Save the FINAL fitted workflow
    saveRDS(final_ames_fit, "ames_model.rds")

    # Reload — no extra steps needed
    final_ames_fit_loaded <- readRDS("ames_model.rds")

    # Make predictions again to prove it works
    predict(final_ames_fit_loaded, new_data = ames_test) |> head()
    #> 19/19 - 0s - 10ms/step
    #> # A tibble: 6 × 1
    #>     .pred
    #>     <dbl>
    #> 1 193897.
    #> 2 195599.
    #> 3 234444.
    #> 4 223605.
    #> 5 244144.
    #> 6 125377.

If you need a fully self-contained bundle suitable for deployment with `vetiver` or other MLOps tools, use `bundle::bundle()` instead:

    library(bundle)

    # Save as a portable bundle
    bundled <- bundle(final_ames_fit)
    saveRDS(bundled, "ames_model_bundle.rds")

    # Reload in any R session
    library(kerasnip)
    library(bundle)
    final_ames_fit_loaded <- unbundle(readRDS("ames_model_bundle.rds"))

    predict(final_ames_fit_loaded, new_data = ames_test) |> head()
    #> 19/19 - 0s - 11ms/step
    #> # A tibble: 6 × 1
    #>     .pred
    #>     <dbl>
    #> 1 193897.
    #> 2 195599.
    #> 3 234444.
    #> 4 223605.
    #> 5 244144.
    #> 6 125377.

See `vignette("saving_and_reloading")` for a detailed comparison of both approaches.