[R-package] Add print() and summary() methods for Booster

R-package/NAMESPACE

@@ -6,9 +6,11 @@ S3method(dimnames,lgb.Dataset)
 S3method(get_field,lgb.Dataset)
 S3method(getinfo,lgb.Dataset)
 S3method(predict,lgb.Booster)
+S3method(print,lgb.Booster)
 S3method(set_field,lgb.Dataset)
 S3method(setinfo,lgb.Dataset)
 S3method(slice,lgb.Dataset)
+S3method(summary,lgb.Booster)
 export(get_field)
 export(getinfo)
 export(lgb.Dataset)

R-package/R/lgb.Booster.R

@@ -810,6 +810,54 @@ predict.lgb.Booster <- function(object,
   )
 }
 
+#' @name print.lgb.Booster
+#' @title Print method for LightGBM model
+#' @description Show summary information about a LightGBM model object (same as \code{summary}).
+#' @param x Object of class \code{lgb.Booster}
+#' @param ... Not used
+#' @return The same input `x`, returned as invisible.
+#' @export
+print.lgb.Booster <- function(x, ...) {
+  handle <- x$.__enclos_env__$private$handle
+  handle_is_null <- lgb.is.null.handle(handle)
+
+  if (!handle_is_null) {
+    cat(sprintf("LightGBM Model (%d trees)\n", x$current_iter()))
+  } else {
+    cat("LightGBM Model\n")
+  }
+
+  if (!handle_is_null) {
+    if (x$.__enclos_env__$private$num_class == 1L) {
+      cat(sprintf("Objective: %s\n", x$params$objective))
+    } else {
+      cat(sprintf("Objective: %s (%d classes)\n"
+          , x$params$objective
+          , x$.__enclos_env__$private$num_class == 1L))
+    }
+  } else {
+    cat("(Booster handle is invalid)\n")
+  }
+
+  if (!handle_is_null) {
+    ncols <- .Call(LGBM_BoosterGetNumFeatures_R, handle)
+    cat(sprintf("Fitted to dataset with %d columns\n", ncols))
+  }
+
+  return(invisible(x))
+}
+
+#' @name summary.lgb.Booster
+#' @title Summary method for LightGBM model
+#' @description Show summary information about a LightGBM model object (same as \code{print}).
+#' @param object Object of class \code{lgb.Booster}
+#' @param ... Not used
+#' @return The same input `object`, returned as invisible.
+#' @export
+summary.lgb.Booster <- function(object, ...) {
+  print(object)
+}
+
 #' @name lgb.load
 #' @title Load LightGBM model
 #' @description Load LightGBM takes in either a file path or model string.

R-package/src/lightgbm_R.cpp

@@ -525,6 +525,15 @@ SEXP LGBM_BoosterGetNumClasses_R(SEXP handle,
   R_API_END();
 }
 
+SEXP LGBM_BoosterGetNumFeatures_R(SEXP handle) {
+  R_API_BEGIN();
+  _AssertBoosterHandleNotNull(handle);
+  int out = 0;
+  CHECK_CALL(LGBM_BoosterGetNumFeatures(R_ExternalPtrAddr(handle), &out));
+  return Rf_ScalarInteger(out);
+  R_API_END();
+}
+
 SEXP LGBM_BoosterUpdateOneIter_R(SEXP handle) {
   R_API_BEGIN();
   _AssertBoosterHandleNotNull(handle);
@@ -889,6 +898,7 @@ static const R_CallMethodDef CallEntries[] = {
   {"LGBM_BoosterResetTrainingData_R"  , (DL_FUNC) &LGBM_BoosterResetTrainingData_R  , 2},
   {"LGBM_BoosterResetParameter_R"     , (DL_FUNC) &LGBM_BoosterResetParameter_R     , 2},
   {"LGBM_BoosterGetNumClasses_R"      , (DL_FUNC) &LGBM_BoosterGetNumClasses_R      , 2},
+  {"LGBM_BoosterGetNumFeatures_R"     , (DL_FUNC) &LGBM_BoosterGetNumFeatures_R     , 1},
   {"LGBM_BoosterUpdateOneIter_R"      , (DL_FUNC) &LGBM_BoosterUpdateOneIter_R      , 1},
   {"LGBM_BoosterUpdateOneIterCustom_R", (DL_FUNC) &LGBM_BoosterUpdateOneIterCustom_R, 4},
   {"LGBM_BoosterRollbackOneIter_R"    , (DL_FUNC) &LGBM_BoosterRollbackOneIter_R    , 1},

R-package/src/lightgbm_R.h

@@ -302,6 +302,15 @@ LIGHTGBM_C_EXPORT SEXP LGBM_BoosterGetNumClasses_R(
   SEXP out
 );
 
+/*!
+* \brief Get number of features
+* \param handle Booster handle
+* \return R integer
+*/
+LIGHTGBM_C_EXPORT SEXP LGBM_BoosterGetNumFeatures_R(
+  SEXP handle
+);
+
 /*!
 * \brief update the model in one round
 * \param handle Booster handle

include/LightGBM/c_api.h

@@ -1263,6 +1263,15 @@ LIGHTGBM_C_EXPORT int LGBM_BoosterSetLeafValue(BoosterHandle handle,
                                                int leaf_idx,
                                                double val);
 
+/*!
+ * \brief Get number of features (columns) to which a booster was fit.
+ * \param handle Handle of booster
+ * \param[out] out_val Output result from the specified leaf
+ * \return 0 when succeed, -1 when failure happens
+ */
+LIGHTGBM_C_EXPORT int LGBM_BoosterGetNumFeatures(BoosterHandle handle,
+                                                 int *out_val);
+
 /*!
  * \brief Get model feature importance.
  * \param handle Handle of booster

src/c_api.cpp

@@ -2308,6 +2308,13 @@ int LGBM_BoosterSetLeafValue(BoosterHandle handle,
   API_END();
 }
 
+int LGBM_BoosterGetNumFeatures(BoosterHandle handle, int *out_val) {
+  API_BEGIN();
+  Booster* ref_booster = reinterpret_cast<Booster*>(handle);
+  *out_val = ref_booster->GetBoosting()->MaxFeatureIdx() + 1;
+  API_END();
+}
+
 int LGBM_BoosterFeatureImportance(BoosterHandle handle,
                                   int num_iteration,
                                   int importance_type,