Reference

Package description, glossary, and included data sets
loo-package	Efficient LOO-CV and WAIC for Bayesian models
loo-glossary	LOO package glossary
loo-datasets	Datasets for loo examples and vignettes
Approximate LOO-CV Approximate LOO-CV, Pareto smoothed importance sampling (PSIS), and diagnostics.
loo() loo_i() is.loo() is.psis_loo()	Efficient approximate leave-one-out cross-validation (LOO)
loo_subsample()	Efficient approximate leave-one-out cross-validation (LOO) using subsampling
loo_approximate_posterior()	Efficient approximate leave-one-out cross-validation (LOO) for posterior approximations
E_loo()	Compute weighted expectations
weights(<importance_sampling>) psis() is.psis() is.sis() is.tis()	Pareto smoothed importance sampling (PSIS)
pareto_k_table() pareto_k_ids() pareto_k_values() psis_n_eff_values() mcse_loo() plot(<psis_loo>) plot(<psis>)	Diagnostics for Pareto smoothed importance sampling (PSIS)
Model comparison and weighting/averaging Functions for comparing models and computing model weights via stacking of predictive distributions or pseudo-BMA weighting.
loo_compare() print(<compare.loo>) print(<compare.loo_ss>)	Model comparison
loo_model_weights() stacking_weights() pseudobma_weights()	Model averaging/weighting via stacking or pseudo-BMA weighting
Helper functions for K-fold CV
kfold_split_random() kfold_split_stratified() kfold_split_grouped()	Helper functions for K-fold cross-validation
kfold() is.kfold()	Generic function for K-fold cross-validation for developers
Other functions
waic() is.waic()	Widely applicable information criterion (WAIC)
extract_log_lik()	Extract pointwise log-likelihood from a Stan model
relative_eff()	Convenience function for computing relative efficiencies
gpdfit()	Estimate parameters of the Generalized Pareto distribution
example_loglik_array() example_loglik_matrix()	Objects to use in examples and tests
print(<loo>) print(<waic>) print(<psis_loo>) print(<importance_sampling_loo>) print(<psis_loo_ap>) print(<psis>) print(<importance_sampling>)	Print methods
Deprecated functions
compare()	Model comparison (deprecated, old version)
psislw()	Pareto smoothed importance sampling (deprecated, old version)