Compile Keras Models Over a Grid of Hyperparameters — compile_keras

Pre-compiles Keras models for each hyperparameter combination in a grid.

This function is a powerful debugging tool to use before running a full tune::tune_grid(). It allows you to quickly validate multiple model architectures, ensuring they can be successfully built and compiled without the time-consuming process of actually fitting them. It helps catch common errors like incompatible layer shapes or invalid argument values early.

Usage

compile_keras_grid(spec, grid, x, y)

Arguments

spec: A parsnip model specification created by create_keras_sequential_spec() or create_keras_functional_spec().
grid: A tibble or data.frame containing the grid of hyperparameters to evaluate. Each row represents a unique model architecture to be compiled.
x: A data frame or matrix of predictors. This is used to infer the input_shape for the Keras model.
y: A vector or factor of outcomes. This is used to infer the output shape and the default loss function for the Keras model.

Value

A tibble with the following columns:

Columns from the input grid.
compiled_model: A list-column containing the compiled Keras model objects. If compilation failed, the element will be NULL.
error: A list-column containing NA for successes or a character string with the error message for failures.

Details

Compile and Validate Keras Model Architectures

The function iterates through each row of the provided grid. For each hyperparameter combination, it attempts to build and compile the Keras model defined by the spec. The process is wrapped in a try-catch block to gracefully handle and report any errors that occur during model instantiation or compilation.

The output is a tibble that mirrors the input grid, with additional columns containing the compiled model object or the error message, making it easy to inspect which architectures are valid.

Examples

# \donttest{
if (requireNamespace("keras3", quietly = TRUE)) {
library(keras3)
library(parsnip)
library(dials)

# 1. Define layer blocks
input_block <- function(model, input_shape) {
  keras_model_sequential(input_shape = input_shape)
}
hidden_block <- function(model, units = 32) {
  model |> layer_dense(units = units, activation = "relu")
}
output_block <- function(model, num_classes) {
  model |> layer_dense(units = num_classes, activation = "softmax")
}

# 2. Define a kerasnip model specification
create_keras_sequential_spec(
  model_name = "my_mlp_grid",
  layer_blocks = list(
    input = input_block,
    hidden = hidden_block,
    output = output_block
  ),
  mode = "classification"
)

mlp_spec <- my_mlp_grid(
  hidden_units = tune(),
  compile_loss = "categorical_crossentropy",
  compile_optimizer = "adam"
)

# 3. Create a hyperparameter grid
# Include an invalid value (-10) to demonstrate error handling
param_grid <- tibble::tibble(
  hidden_units = c(32, 64, -10)
)

# 4. Prepare dummy data
x_train <- matrix(rnorm(100 * 10), ncol = 10)
y_train <- factor(sample(0:1, 100, replace = TRUE))

# 5. Compile models over the grid
compiled_grid <- compile_keras_grid(
  spec = mlp_spec,
  grid = param_grid,
  x = x_train,
  y = y_train
)

print(compiled_grid)
remove_keras_spec("my_mlp_grid")

# 6. Inspect the results
# The row with `hidden_units = -10` will show an error.
}
#> 
#> Attaching package: ‘parsnip’
#> The following object is masked from ‘package:kerasnip’:
#> 
#>     get_model_env
#> Loading required package: scales
#> # A tibble: 3 × 3
#>   hidden_units compiled_model                           error                   
#>          <dbl> <list>                                   <chr>                   
#> 1           32 <keras.src.models.sequential.Sequential>  NA                     
#> 2           64 <keras.src.models.sequential.Sequential>  NA                     
#> 3          -10 <NULL>                                   "ValueError: Cannot con…
#> Removed from parsnip registry objects: my_mlp_grid, my_mlp_grid_args, my_mlp_grid_encoding, my_mlp_grid_fit, my_mlp_grid_modes, my_mlp_grid_pkgs, my_mlp_grid_predict
#> Removed 'my_mlp_grid' from parsnip:::get_model_env()$models
# }