Updated docstrings

NEWS.md

@@ -3,6 +3,7 @@
 ## Documentation
 
 - More compact README.
+- Updated function description.
 
 # kernelshap 0.7.0
 

R/additive_shap.R

@@ -9,19 +9,20 @@
 #' - `gam::gam()`,
 #' - [survival::coxph()], and
 #' - [survival::survreg()].
-#' 
+#'
 #' The SHAP values are extracted via `predict(object, newdata = X, type = "terms")`,
-#' a logic heavily inspired by `fastshap:::explain.lm(..., exact = TRUE)`.
+#' a logic adopted from `fastshap:::explain.lm(..., exact = TRUE)`.
 #' Models with interactions (specified via `:` or `*`), or with terms of
 #' multiple features like `log(x1/x2)` are not supported.
-#' 
+#'
 #' Note that the SHAP values obtained by [additive_shap()] are expected to
 #' match those of [permshap()] and [kernelshap()] as long as their background
 #' data equals the full training data (which is typically not feasible).
 #'
-#' @inheritParams kernelshap
-#' @param X Dataframe with rows to be explained. Will be used like
+#' @param object Fitted additive model.
+#' @param X Dataframe with rows to be explained. Passed to
 #'   `predict(object, newdata = X, type = "terms")`.
+#' @param verbose Set to `FALSE` to suppress messages.
 #' @param ... Currently unused.
 #' @returns
 #'   An object of class "kernelshap" with the following components:
@@ -38,15 +39,15 @@
 #' fit <- lm(Sepal.Length ~ ., data = iris)
 #' s <- additive_shap(fit, head(iris))
 #' s
-#' 
+#'
 #' # MODEL TWO: More complicated (but not very clever) formula
 #' fit <- lm(
 #'   Sepal.Length ~ poly(Sepal.Width, 2) + log(Petal.Length) + log(Sepal.Width),
 #'   data = iris
 #' )
 #' s_add <- additive_shap(fit, head(iris))
 #' s_add
-#' 
+#'
 #' # Equals kernelshap()/permshap() when background data is full training data
 #' s_kernel <- kernelshap(
 #'  fit, head(iris[c("Sepal.Width", "Petal.Length")]), bg_X = iris
@@ -59,28 +60,28 @@ additive_shap <- function(object, X, verbose = TRUE, ...) {
   if (any(attr(stats::terms(object), "order") > 1)) {
     stop("Additive SHAP not appropriate for models with interactions.")
   }
-  
+
   txt <- "Exact additive SHAP via predict(..., type = 'terms')"
   if (verbose) {
     message(txt)
   }
-  
+
   S <- stats::predict(object, newdata = X, type = "terms")
   rownames(S) <- NULL
-  
+
   # Baseline value
   b <- as.vector(attr(S, "constant"))
   if (is.null(b)) {
     b <- 0
   }
-  
+
   # Which columns of X are used in each column of S?
   s_names <- colnames(S)
   cols_used <- lapply(s_names, function(z) all.vars(stats::reformulate(z)))
   if (any(lengths(cols_used) > 1L)) {
     stop("The formula contains terms with multiple features (not supported).")
   }
-  
+
   # Collapse all columns in S using the same column in X and rename accordingly
   mapping <- split(
     s_names, factor(unlist(cols_used), levels = colnames(X)), drop = TRUE
@@ -89,7 +90,7 @@ additive_shap <- function(object, X, verbose = TRUE, ...) {
     cbind,
     lapply(mapping, function(z) rowSums(S[, z, drop = FALSE], na.rm = TRUE))
   )
-  
+
   structure(
     list(
       S = S,

R/permshap.R

@@ -2,7 +2,7 @@
 #'
 #' Exact permutation SHAP algorithm with respect to a background dataset,
 #' see Strumbelj and Kononenko. The function works for up to 14 features.
-#' For eight or more features, we recomment to switch to [kernelshap()].
+#' For more than eight features, we recommend [kernelshap()] due to its higher speed.
 #'
 #' @inheritParams kernelshap
 #' @returns
@@ -16,12 +16,12 @@
 #'   - `bg_w`: The background case weights.
 #'   - `m_exact`: Integer providing the effective number of exact on-off vectors used.
 #'   - `exact`: Logical flag indicating whether calculations are exact or not
-#'     (currently `TRUE`).
+#'     (currently always `TRUE`).
 #'   - `txt`: Summary text.
 #'   - `predictions`: \eqn{(n \times K)} matrix with predictions of `X`.
 #'   - `algorithm`: "permshap".
 #' @references
-#'   1. Erik Strumbelj and Igor Kononenko. Explaining prediction models and individual 
+#'   1. Erik Strumbelj and Igor Kononenko. Explaining prediction models and individual
 #'     predictions with feature contributions. Knowledge and Information Systems 41, 2014.
 #' @export
 #' @examples
@@ -80,7 +80,7 @@ permshap.default <- function(
   if (verbose) {
     message(txt)
   }
-  
+
   basic_checks(X = X, feature_names = feature_names, pred_fun = pred_fun)
   prep_bg <- prepare_bg(X = X, bg_X = bg_X, bg_n = bg_n, bg_w = bg_w, verbose = verbose)
   bg_X <- prep_bg$bg_X
@@ -92,32 +92,32 @@ permshap.default <- function(
   bg_preds <- align_pred(pred_fun(object, bg_X, ...))
   v0 <- wcolMeans(bg_preds, w = bg_w)         # Average pred of bg data: 1 x K
   v1 <- align_pred(pred_fun(object, X, ...))  # Predictions on X:        n x K
-  
+
   # Drop unnecessary columns in bg_X. If X is matrix, also column order is relevant
   # Predictions will never be applied directly to bg_X anymore
   if (!identical(colnames(bg_X), feature_names)) {
     bg_X <- bg_X[, feature_names, drop = FALSE]
   }
-  
+
   # Precalculations that are identical for each row to be explained
   Z <- exact_Z(p, feature_names = feature_names, keep_extremes = TRUE)
   m_exact <- nrow(Z) - 2L  # We won't evaluate vz for first and last row
   precalc <- list(
     Z = Z,
-    Z_code = rowpaste(Z), 
+    Z_code = rowpaste(Z),
     bg_X_rep = rep_rows(bg_X, rep.int(seq_len(bg_n), m_exact))
   )
-  
+
   if (m_exact * bg_n > 2e5) {
     warning_burden(m_exact, bg_n = bg_n)
   }
-  
+
   # Apply permutation SHAP to each row of X
   if (isTRUE(parallel)) {
     parallel_args <- c(list(i = seq_len(n)), parallel_args)
     res <- do.call(foreach::foreach, parallel_args) %dopar% permshap_one(
       x = X[i, , drop = FALSE],
-      v1 = v1[i, , drop = FALSE], 
+      v1 = v1[i, , drop = FALSE],
       object = object,
       pred_fun = pred_fun,
       bg_w = bg_w,
@@ -133,7 +133,7 @@ permshap.default <- function(
     for (i in seq_len(n)) {
       res[[i]] <- permshap_one(
         x = X[i, , drop = FALSE],
-        v1 = v1[i, , drop = FALSE], 
+        v1 = v1[i, , drop = FALSE],
         object = object,
         pred_fun = pred_fun,
         bg_w = bg_w,

README.md

@@ -15,19 +15,18 @@
 
 The package contains three functions to crunch SHAP values:
 
-- `permshap()`: Exact permutation SHAP algorithm of [1]. Recommended for models with up to 8 features.
-- `kernelshap()`: Kernel SHAP algorithm of [2] and [3]. Recommended for models with more than 8 features.
-- `additive_shap()`: For *additive models* fitted via `lm()`, `glm()`, `mgcv::gam()`, `mgcv::bam()`, `gam::gam()`, `survival::coxph()`, or `survival::survreg()`. Exponentially faster than the model-agnostic options above, and recommended if possible.
+- **`permshap()`**: Exact permutation SHAP algorithm of [1]. Recommended for models with up to 8 features.
+- **`kernelshap()`**: Kernel SHAP algorithm of [2] and [3]. Recommended for models with more than 8 features.
+- **`additive_shap()`**: For *additive models* fitted via `lm()`, `glm()`, `mgcv::gam()`, `mgcv::bam()`, `gam::gam()`, `survival::coxph()`, or `survival::survreg()`. Exponentially faster than the model-agnostic options above, and recommended if possible.
 
-To explain your model, select an explanation dataset `X` (up to 1000 rows from the training data) and apply the recommended function. Use {shapviz} to visualize the resulting SHAP values. 
+To explain your model, select an explanation dataset `X` (up to 1000 rows from the training data, feature columns only) and apply the recommended function. Use {shapviz} to visualize the resulting SHAP values. 
 
-**Remarks for `permshap()` and `kernelshap()`**
+**Remarks to `permshap()` and `kernelshap()`**
 
-- `X` should only contain feature columns.
 - Both algorithms need a representative background data `bg_X` to calculate marginal means (up to 500 rows from the training data). In cases with a natural "off" value (like MNIST digits), this can also be a single row with all values set to the off value. If unspecified, 200 rows are randomly sampled from `X`.
-- By changing the defaults in `kernelshap()`, the iterative pure sampling approach of [3] can be enforced.
-- `permshap()` vs. `kernelshap()`: For models with interactions of order up to two, exact Kernel SHAP agrees with exact permutation SHAP.
-- `additive_shap()` vs. the model-agnostic explainers: The results would agree if the full training data would be used as background data.
+- Exact Kernel SHAP is an approximation to exact permutation SHAP. Since exact calculations are usually sufficiently fast for up to eight features, we recommend `permshap()` in this case. With more features, `kernelshap()` switches to a comparably fast, almost exact algorithm. That is why we recommend `kernelshap()` in this case.
+- For models with interactions of order up to two, SHAP values of exact permutation SHAP and exact Kernel SHAP agree.
+- `permshap()` and `kernelshap()` give the same results as `additive_shap` as long as the full training data would be used as background data.
 
 ## Installation