ex6

library(tidyverse)

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library(tidymodels)

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library(ISLR)
library(glmnet)

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## Loaded glmnet 4.1-8

data(Hitters)
Hitters <- Hitters %>% drop_na()

set.seed(123)
data_split <- initial_split(Hitters, prop = 0.75)
train_data <- training(data_split)
test_data <- testing(data_split)

hitters_recipe <- recipe(Salary ~ ., data = train_data) %>%
  step_dummy(all_nominal_predictors()) %>%
  step_zv(all_predictors()) %>%
  step_normalize(all_predictors())
ridge_spec <- linear_reg(penalty = tune(), mixture = 0) %>%
  set_engine("glmnet")

ridge_workflow <- workflow() %>%
  add_model(ridge_spec) %>%
  add_recipe(hitters_recipe)

set.seed(234)
folds <- vfold_cv(train_data, v = 10)
lambda_grid <- grid_regular(penalty(), levels = 50)

ridge_results <- tune_grid(
  ridge_workflow,
  resamples = folds,
  grid = lambda_grid
)

autoplot(ridge_results) + ggtitle("Ridge Regression - RMSE vs Penalty")

best_ridge <- select_best(x = ridge_results, metric = "rmse")
final_ridge <- finalize_workflow(ridge_workflow, best_ridge)
ridge_fit <- fit(final_ridge, data = train_data)
ridge_fit %>% 
  pull_workflow_fit() %>% 
  tidy() %>% 
  filter(term != "(Intercept)") %>%
  ggplot(aes(x = reorder(term, estimate), y = estimate)) +
  geom_col() +
  coord_flip() +
  ggtitle("Ridge Coefficients")

## Warning: `pull_workflow_fit()` was deprecated in workflows 0.2.3.
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lasso_spec <- linear_reg(penalty = tune(), mixture = 1) %>%
  set_engine("glmnet")

lasso_workflow <- workflow() %>%
  add_model(lasso_spec) %>%
  add_recipe(hitters_recipe)

lasso_results <- tune_grid(
  lasso_workflow,
  resamples = folds,
  grid = lambda_grid
)

autoplot(lasso_results) + ggtitle("Lasso Regression - RMSE vs Penalty")

best_lasso <- select_best(x = lasso_results, metric = "rmse")
final_lasso <- finalize_workflow(lasso_workflow, best_lasso)
lasso_fit <- fit(final_lasso, data = train_data)
lasso_fit %>% 
  pull_workflow_fit() %>% 
  tidy() %>% 
  filter(term != "(Intercept)") %>%
  ggplot(aes(x = reorder(term, estimate), y = estimate)) +
  geom_col() +
  coord_flip() +
  ggtitle("Lasso Coefficients")