From fa2215eec48f371bd192c1d04bb05a302fe990dc Mon Sep 17 00:00:00 2001
From: David Cortes <david.cortes.rivera@gmail.com>
Date: Thu, 14 Oct 2021 23:35:17 -0300
Subject: [PATCH 01/17] add print and summary S3 method

---
 R-package/NAMESPACE                  |  2 ++
 R-package/R/lgb.Booster.R            | 47 ++++++++++++++++++++++++++++
 R-package/man/print.lgb.Booster.Rd   | 17 ++++++++++
 R-package/man/summary.lgb.Booster.Rd | 19 +++++++++++
 R-package/src/lightgbm_R.cpp         | 10 ++++++
 R-package/src/lightgbm_R.h           |  9 ++++++
 include/LightGBM/c_api.h             |  9 ++++++
 src/c_api.cpp                        |  7 +++++
 8 files changed, 120 insertions(+)
 create mode 100644 R-package/man/print.lgb.Booster.Rd
 create mode 100644 R-package/man/summary.lgb.Booster.Rd

diff --git a/R-package/NAMESPACE b/R-package/NAMESPACE
index 8df060d28605..99139fe99276 100644
--- a/R-package/NAMESPACE
+++ b/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)
diff --git a/R-package/R/lgb.Booster.R b/R-package/R/lgb.Booster.R
index 586f3a38899d..995fee6e1103 100644
--- a/R-package/R/lgb.Booster.R
+++ b/R-package/R/lgb.Booster.R
@@ -810,6 +810,53 @@ 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}
+#' @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.
diff --git a/R-package/man/print.lgb.Booster.Rd b/R-package/man/print.lgb.Booster.Rd
new file mode 100644
index 000000000000..2e0c3f97ba95
--- /dev/null
+++ b/R-package/man/print.lgb.Booster.Rd
@@ -0,0 +1,17 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/lgb.Booster.R
+\name{print.lgb.Booster}
+\alias{print.lgb.Booster}
+\title{Print method for LightGBM model}
+\usage{
+\method{print}{lgb.Booster}(x)
+}
+\arguments{
+\item{x}{Object of class \code{lgb.Booster}}
+}
+\value{
+The same input `x`, returned as invisible.
+}
+\description{
+Show summary information about a LightGBM model object (same as \code{summary}).
+}
diff --git a/R-package/man/summary.lgb.Booster.Rd b/R-package/man/summary.lgb.Booster.Rd
new file mode 100644
index 000000000000..8af5158feb15
--- /dev/null
+++ b/R-package/man/summary.lgb.Booster.Rd
@@ -0,0 +1,19 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/lgb.Booster.R
+\name{summary.lgb.Booster}
+\alias{summary.lgb.Booster}
+\title{Summary method for LightGBM model}
+\usage{
+\method{summary}{lgb.Booster}(object, ...)
+}
+\arguments{
+\item{object}{Object of class \code{lgb.Booster}}
+
+\item{...}{Not used}
+}
+\value{
+The same input `object`, returned as invisible.
+}
+\description{
+Show summary information about a LightGBM model object (same as \code{print}).
+}
diff --git a/R-package/src/lightgbm_R.cpp b/R-package/src/lightgbm_R.cpp
index 99dd666dbf9e..43eb40db5a38 100644
--- a/R-package/src/lightgbm_R.cpp
+++ b/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},
diff --git a/R-package/src/lightgbm_R.h b/R-package/src/lightgbm_R.h
index 16a87c3a611f..070e107a8a4f 100644
--- a/R-package/src/lightgbm_R.h
+++ b/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
diff --git a/include/LightGBM/c_api.h b/include/LightGBM/c_api.h
index b5542891b063..bdeb245ae1be 100644
--- a/include/LightGBM/c_api.h
+++ b/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
diff --git a/src/c_api.cpp b/src/c_api.cpp
index bc3bfc3b2434..be5ccc400e43 100644
--- a/src/c_api.cpp
+++ b/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,

From fa9e8e92ed6ccc6d0686fe8b17c036d178ad264b Mon Sep 17 00:00:00 2001
From: David Cortes <david.cortes.rivera@gmail.com>
Date: Thu, 14 Oct 2021 23:53:12 -0300
Subject: [PATCH 02/17] correct wrong signature

---
 R-package/R/lgb.Booster.R          | 3 ++-
 R-package/man/print.lgb.Booster.Rd | 4 +++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/R-package/R/lgb.Booster.R b/R-package/R/lgb.Booster.R
index 995fee6e1103..3accedd404d8 100644
--- a/R-package/R/lgb.Booster.R
+++ b/R-package/R/lgb.Booster.R
@@ -814,9 +814,10 @@ predict.lgb.Booster <- function(object,
 #' @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) {
+print.lgb.Booster <- function(x, ...) {
   handle <- x$.__enclos_env__$private$handle
   handle_is_null <- lgb.is.null.handle(handle)
 
diff --git a/R-package/man/print.lgb.Booster.Rd b/R-package/man/print.lgb.Booster.Rd
index 2e0c3f97ba95..47ae13189891 100644
--- a/R-package/man/print.lgb.Booster.Rd
+++ b/R-package/man/print.lgb.Booster.Rd
@@ -4,10 +4,12 @@
 \alias{print.lgb.Booster}
 \title{Print method for LightGBM model}
 \usage{
-\method{print}{lgb.Booster}(x)
+\method{print}{lgb.Booster}(x, ...)
 }
 \arguments{
 \item{x}{Object of class \code{lgb.Booster}}
+
+\item{...}{Not used}
 }
 \value{
 The same input `x`, returned as invisible.

From 1c5dd263464abacd0fc9e002bd423db3ca3606cd Mon Sep 17 00:00:00 2001
From: David Cortes <david.cortes.rivera@gmail.com>
Date: Fri, 15 Oct 2021 00:12:37 -0300
Subject: [PATCH 03/17] attempt at bypassing linter

---
 R-package/R/lgb.Booster.R | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/R-package/R/lgb.Booster.R b/R-package/R/lgb.Booster.R
index 3accedd404d8..29bcd4b4050e 100644
--- a/R-package/R/lgb.Booster.R
+++ b/R-package/R/lgb.Booster.R
@@ -818,6 +818,7 @@ predict.lgb.Booster <- function(object,
 #' @return The same input `x`, returned as invisible.
 #' @export
 print.lgb.Booster <- function(x, ...) {
+  # nolint start
   handle <- x$.__enclos_env__$private$handle
   handle_is_null <- lgb.is.null.handle(handle)
 
@@ -843,6 +844,7 @@ print.lgb.Booster <- function(x, ...) {
     ncols <- .Call(LGBM_BoosterGetNumFeatures_R, handle)
     cat(sprintf("Fitted to dataset with %d columns\n", ncols))
   }
+  # nolint end
 
   return(invisible(x))
 }

From 38d5db6b92693109c458602bf77b00f32e4c8c68 Mon Sep 17 00:00:00 2001
From: david-cortes <david.cortes.rivera@gmail.com>
Date: Fri, 15 Oct 2021 06:43:55 +0300
Subject: [PATCH 04/17] Update R-package/R/lgb.Booster.R

Co-authored-by: James Lamb <jaylamb20@gmail.com>
---
 R-package/R/lgb.Booster.R | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/R-package/R/lgb.Booster.R b/R-package/R/lgb.Booster.R
index 29bcd4b4050e..2d72a0bdd84a 100644
--- a/R-package/R/lgb.Booster.R
+++ b/R-package/R/lgb.Booster.R
@@ -834,7 +834,7 @@ print.lgb.Booster <- function(x, ...) {
     } else {
       cat(sprintf("Objective: %s (%d classes)\n"
           , x$params$objective
-          , x$.__enclos_env__$private$num_class == 1L))
+          , x$.__enclos_env__$private$num_class))
     }
   } else {
     cat("(Booster handle is invalid)\n")

From 4746829ff3b2004b9b28833d81f573011b93f257 Mon Sep 17 00:00:00 2001
From: david-cortes <david.cortes.rivera@gmail.com>
Date: Fri, 15 Oct 2021 06:44:07 +0300
Subject: [PATCH 05/17] Update R-package/src/lightgbm_R.h

Co-authored-by: James Lamb <jaylamb20@gmail.com>
---
 R-package/src/lightgbm_R.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/R-package/src/lightgbm_R.h b/R-package/src/lightgbm_R.h
index 070e107a8a4f..9883b0477d19 100644
--- a/R-package/src/lightgbm_R.h
+++ b/R-package/src/lightgbm_R.h
@@ -303,7 +303,7 @@ LIGHTGBM_C_EXPORT SEXP LGBM_BoosterGetNumClasses_R(
 );
 
 /*!
-* \brief Get number of features
+* \brief  Get number of features in the training data used when fitting this Booster.
 * \param handle Booster handle
 * \return R integer
 */

From 2f96422332a55d745ec0b242065b858fed19e4ef Mon Sep 17 00:00:00 2001
From: david-cortes <david.cortes.rivera@gmail.com>
Date: Fri, 15 Oct 2021 06:44:32 +0300
Subject: [PATCH 06/17] Update include/LightGBM/c_api.h

Co-authored-by: James Lamb <jaylamb20@gmail.com>
---
 include/LightGBM/c_api.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/LightGBM/c_api.h b/include/LightGBM/c_api.h
index bdeb245ae1be..6c76278439f5 100644
--- a/include/LightGBM/c_api.h
+++ b/include/LightGBM/c_api.h
@@ -1264,9 +1264,9 @@ LIGHTGBM_C_EXPORT int LGBM_BoosterSetLeafValue(BoosterHandle handle,
                                                double val);
 
 /*!
- * \brief Get number of features (columns) to which a booster was fit.
+ * \brief Get number of features in the training data used when fitting this Booster.
  * \param handle Handle of booster
- * \param[out] out_val Output result from the specified leaf
+ * \param[out] out_val Number of features in the training data used when fitting this Booster.
  * \return 0 when succeed, -1 when failure happens
  */
 LIGHTGBM_C_EXPORT int LGBM_BoosterGetNumFeatures(BoosterHandle handle,

From 8b40215ee924ca8ef828ea2a38a3cd1e11c7e788 Mon Sep 17 00:00:00 2001
From: David Cortes <david.cortes.rivera@gmail.com>
Date: Fri, 15 Oct 2021 13:35:08 -0300
Subject: [PATCH 07/17] add more tests

---
 R-package/tests/testthat/test_lgb.Booster.R | 62 +++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/R-package/tests/testthat/test_lgb.Booster.R b/R-package/tests/testthat/test_lgb.Booster.R
index b76acd9d9d09..cd6d9a66e202 100644
--- a/R-package/tests/testthat/test_lgb.Booster.R
+++ b/R-package/tests/testthat/test_lgb.Booster.R
@@ -1035,3 +1035,65 @@ test_that("boosters with linear models at leaves can be written to RDS and re-lo
     preds2 <- predict(bst2, X)
     expect_identical(preds, preds2)
 })
+
+test_that("Booster's print, show, and summary work correctly", {
+    check_methods_work <- function(model) {
+        expect_error(print(model), NA)
+        expect_error(show(model), NA)
+        expect_error(summary(model), NA)
+        model$finalize()
+        expect_error(print(model), NA)
+        expect_error(show(model), NA)
+        expect_error(summary(model), NA)
+    }
+
+    data("mtcars")
+    model <- lgb.train(
+        params = list(objective = "regression")
+        , data = lgb.Dataset(
+            as.matrix(mtcars[, -1])
+            , label = mtcars$mpg)
+        , verbose = 0
+        , nrounds = 5L
+    )
+    check_methods_work(model)
+
+    data("iris")
+    model <- lgb.train(
+        params = list(objective = "multiclass", num_class = 3L)
+        , data = lgb.Dataset(
+            as.matrix(iris[, -5])
+            , label = as.numeric(factor(iris$Species)) - 1
+        )
+        , verbose = 0
+        , nrounds = 5L
+    )
+    check_methods_work(model)
+})
+
+test_that("LGBM_BoosterGetNumFeatures_R returns correct outputs", {
+    data("mtcars")
+    model <- lgb.train(
+        params = list(objective = "regression")
+        , data = lgb.Dataset(
+            as.matrix(mtcars[, -1])
+            , label = mtcars$mpg)
+        , verbose = 0
+        , nrounds = 5L
+    )
+    ncols <- .Call(LGBM_BoosterGetNumFeatures_R, model$.__enclos_env__$private$handle)
+    expect_equal(ncols, ncol(mtcars) - 1L)
+
+    data("iris")
+    model <- lgb.train(
+        params = list(objective = "multiclass", num_class = 3L)
+        , data = lgb.Dataset(
+            as.matrix(iris[, -5])
+            , label = as.numeric(factor(iris$Species)) - 1
+        )
+        , verbose = 0
+        , nrounds = 5L
+    )
+    ncols <- .Call(LGBM_BoosterGetNumFeatures_R, model$.__enclos_env__$private$handle)
+    expect_equal(ncols, ncol(iris) - 1L)
+})

From 560cbeb80a4b0e3a7a2dee90e70bcba1ef0f17a1 Mon Sep 17 00:00:00 2001
From: David Cortes <david.cortes.rivera@gmail.com>
Date: Fri, 15 Oct 2021 13:46:23 -0300
Subject: [PATCH 08/17] linter

---
 R-package/tests/testthat/test_lgb.Booster.R | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/R-package/tests/testthat/test_lgb.Booster.R b/R-package/tests/testthat/test_lgb.Booster.R
index cd6d9a66e202..1d368be57af4 100644
--- a/R-package/tests/testthat/test_lgb.Booster.R
+++ b/R-package/tests/testthat/test_lgb.Booster.R
@@ -1051,9 +1051,9 @@ test_that("Booster's print, show, and summary work correctly", {
     model <- lgb.train(
         params = list(objective = "regression")
         , data = lgb.Dataset(
-            as.matrix(mtcars[, -1])
+            as.matrix(mtcars[, -1L])
             , label = mtcars$mpg)
-        , verbose = 0
+        , verbose = 0L
         , nrounds = 5L
     )
     check_methods_work(model)
@@ -1062,10 +1062,10 @@ test_that("Booster's print, show, and summary work correctly", {
     model <- lgb.train(
         params = list(objective = "multiclass", num_class = 3L)
         , data = lgb.Dataset(
-            as.matrix(iris[, -5])
-            , label = as.numeric(factor(iris$Species)) - 1
+            as.matrix(iris[, -5L])
+            , label = as.numeric(factor(iris$Species)) - 1.0
         )
-        , verbose = 0
+        , verbose = 0L
         , nrounds = 5L
     )
     check_methods_work(model)
@@ -1076,9 +1076,9 @@ test_that("LGBM_BoosterGetNumFeatures_R returns correct outputs", {
     model <- lgb.train(
         params = list(objective = "regression")
         , data = lgb.Dataset(
-            as.matrix(mtcars[, -1])
+            as.matrix(mtcars[, -1L])
             , label = mtcars$mpg)
-        , verbose = 0
+        , verbose = 0L
         , nrounds = 5L
     )
     ncols <- .Call(LGBM_BoosterGetNumFeatures_R, model$.__enclos_env__$private$handle)
@@ -1088,10 +1088,10 @@ test_that("LGBM_BoosterGetNumFeatures_R returns correct outputs", {
     model <- lgb.train(
         params = list(objective = "multiclass", num_class = 3L)
         , data = lgb.Dataset(
-            as.matrix(iris[, -5])
-            , label = as.numeric(factor(iris$Species)) - 1
+            as.matrix(iris[, -5L])
+            , label = as.numeric(factor(iris$Species)) - 1.0
         )
-        , verbose = 0
+        , verbose = 0L
         , nrounds = 5L
     )
     ncols <- .Call(LGBM_BoosterGetNumFeatures_R, model$.__enclos_env__$private$handle)

From b3e14e60329ca96d1a02433b42282c7d0da363fa Mon Sep 17 00:00:00 2001
From: David Cortes <david.cortes.rivera@gmail.com>
Date: Fri, 15 Oct 2021 13:59:50 -0300
Subject: [PATCH 09/17] don't pluralize single tree

---
 R-package/R/lgb.Booster.R | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/R-package/R/lgb.Booster.R b/R-package/R/lgb.Booster.R
index 2d72a0bdd84a..fbfb6e342ab4 100644
--- a/R-package/R/lgb.Booster.R
+++ b/R-package/R/lgb.Booster.R
@@ -823,7 +823,12 @@ print.lgb.Booster <- function(x, ...) {
   handle_is_null <- lgb.is.null.handle(handle)
 
   if (!handle_is_null) {
-    cat(sprintf("LightGBM Model (%d trees)\n", x$current_iter()))
+    ntrees <- x$current_iter()
+    if (ntrees == 1L) {
+      cat("LightGBM Model (1 tree)\n")
+    } else {
+      cat(sprintf("LightGBM Model (%d trees)\n", ntrees))
+    }
   } else {
     cat("LightGBM Model\n")
   }

From b1b2ab90afefe72ff85581156237734041388764 Mon Sep 17 00:00:00 2001
From: David Cortes <david.cortes.rivera@gmail.com>
Date: Sat, 16 Oct 2021 13:54:11 -0300
Subject: [PATCH 10/17] remove duplicated function

---
 R-package/R/lgb.Booster.R    | 2 +-
 R-package/src/lightgbm_R.cpp | 6 +++---
 include/LightGBM/c_api.h     | 9 ---------
 src/c_api.cpp                | 7 -------
 4 files changed, 4 insertions(+), 20 deletions(-)

diff --git a/R-package/R/lgb.Booster.R b/R-package/R/lgb.Booster.R
index fbfb6e342ab4..912769360d36 100644
--- a/R-package/R/lgb.Booster.R
+++ b/R-package/R/lgb.Booster.R
@@ -846,7 +846,7 @@ print.lgb.Booster <- function(x, ...) {
   }
 
   if (!handle_is_null) {
-    ncols <- .Call(LGBM_BoosterGetNumFeatures_R, handle)
+    ncols <- .Call(LGBM_BoosterGetNumFeature_R, handle)
     cat(sprintf("Fitted to dataset with %d columns\n", ncols))
   }
   # nolint end
diff --git a/R-package/src/lightgbm_R.cpp b/R-package/src/lightgbm_R.cpp
index 43eb40db5a38..2150e652841f 100644
--- a/R-package/src/lightgbm_R.cpp
+++ b/R-package/src/lightgbm_R.cpp
@@ -525,11 +525,11 @@ SEXP LGBM_BoosterGetNumClasses_R(SEXP handle,
   R_API_END();
 }
 
-SEXP LGBM_BoosterGetNumFeatures_R(SEXP handle) {
+SEXP LGBM_BoosterGetNumFeature_R(SEXP handle) {
   R_API_BEGIN();
   _AssertBoosterHandleNotNull(handle);
   int out = 0;
-  CHECK_CALL(LGBM_BoosterGetNumFeatures(R_ExternalPtrAddr(handle), &out));
+  CHECK_CALL(LGBM_BoosterGetNumFeature(R_ExternalPtrAddr(handle), &out));
   return Rf_ScalarInteger(out);
   R_API_END();
 }
@@ -898,7 +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_BoosterGetNumFeature_R"      , (DL_FUNC) &LGBM_BoosterGetNumFeature_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},
diff --git a/include/LightGBM/c_api.h b/include/LightGBM/c_api.h
index 6c76278439f5..b5542891b063 100644
--- a/include/LightGBM/c_api.h
+++ b/include/LightGBM/c_api.h
@@ -1263,15 +1263,6 @@ LIGHTGBM_C_EXPORT int LGBM_BoosterSetLeafValue(BoosterHandle handle,
                                                int leaf_idx,
                                                double val);
 
-/*!
- * \brief Get number of features in the training data used when fitting this Booster.
- * \param handle Handle of booster
- * \param[out] out_val Number of features in the training data used when fitting this Booster.
- * \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
diff --git a/src/c_api.cpp b/src/c_api.cpp
index be5ccc400e43..bc3bfc3b2434 100644
--- a/src/c_api.cpp
+++ b/src/c_api.cpp
@@ -2308,13 +2308,6 @@ 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,

From e7d37c0082c6cec21cb8c81854eba011ebb57d12 Mon Sep 17 00:00:00 2001
From: David Cortes <david.cortes.rivera@gmail.com>
Date: Sat, 16 Oct 2021 14:54:08 -0300
Subject: [PATCH 11/17] update changed function name

---
 R-package/src/lightgbm_R.h                  | 9 ---------
 R-package/tests/testthat/test_lgb.Booster.R | 6 +++---
 2 files changed, 3 insertions(+), 12 deletions(-)

diff --git a/R-package/src/lightgbm_R.h b/R-package/src/lightgbm_R.h
index 9883b0477d19..16a87c3a611f 100644
--- a/R-package/src/lightgbm_R.h
+++ b/R-package/src/lightgbm_R.h
@@ -302,15 +302,6 @@ LIGHTGBM_C_EXPORT SEXP LGBM_BoosterGetNumClasses_R(
   SEXP out
 );
 
-/*!
-* \brief  Get number of features in the training data used when fitting this Booster.
-* \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
diff --git a/R-package/tests/testthat/test_lgb.Booster.R b/R-package/tests/testthat/test_lgb.Booster.R
index 1d368be57af4..a4eef52418bd 100644
--- a/R-package/tests/testthat/test_lgb.Booster.R
+++ b/R-package/tests/testthat/test_lgb.Booster.R
@@ -1071,7 +1071,7 @@ test_that("Booster's print, show, and summary work correctly", {
     check_methods_work(model)
 })
 
-test_that("LGBM_BoosterGetNumFeatures_R returns correct outputs", {
+test_that("LGBM_BoosterGetNumFeature_R returns correct outputs", {
     data("mtcars")
     model <- lgb.train(
         params = list(objective = "regression")
@@ -1081,7 +1081,7 @@ test_that("LGBM_BoosterGetNumFeatures_R returns correct outputs", {
         , verbose = 0L
         , nrounds = 5L
     )
-    ncols <- .Call(LGBM_BoosterGetNumFeatures_R, model$.__enclos_env__$private$handle)
+    ncols <- .Call(LGBM_BoosterGetNumFeature_R, model$.__enclos_env__$private$handle)
     expect_equal(ncols, ncol(mtcars) - 1L)
 
     data("iris")
@@ -1094,6 +1094,6 @@ test_that("LGBM_BoosterGetNumFeatures_R returns correct outputs", {
         , verbose = 0L
         , nrounds = 5L
     )
-    ncols <- .Call(LGBM_BoosterGetNumFeatures_R, model$.__enclos_env__$private$handle)
+    ncols <- .Call(LGBM_BoosterGetNumFeature_R, model$.__enclos_env__$private$handle)
     expect_equal(ncols, ncol(iris) - 1L)
 })

From 0e06c97e88172acd2e3f383e5db545c0c83de68b Mon Sep 17 00:00:00 2001
From: David Cortes <david.cortes.rivera@gmail.com>
Date: Sat, 16 Oct 2021 15:16:57 -0300
Subject: [PATCH 12/17] missing declaration

---
 R-package/src/lightgbm_R.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/R-package/src/lightgbm_R.h b/R-package/src/lightgbm_R.h
index 16a87c3a611f..d9fe51b32f96 100644
--- a/R-package/src/lightgbm_R.h
+++ b/R-package/src/lightgbm_R.h
@@ -302,6 +302,16 @@ LIGHTGBM_C_EXPORT SEXP LGBM_BoosterGetNumClasses_R(
   SEXP out
 );
 
+/*!
+* \brief Get number of features.
+* \param handle Booster handle
+* \param out Total number of features
+* \return R NULL value
+*/
+LIGHTGBM_C_EXPORT SEXP LGBM_BoosterGetNumFeature_R(
+  SEXP handle
+);
+
 /*!
 * \brief update the model in one round
 * \param handle Booster handle

From b44f5d20f82f5943c40f24a03707e8939aa49b6a Mon Sep 17 00:00:00 2001
From: david-cortes <david.cortes.rivera@gmail.com>
Date: Sun, 17 Oct 2021 04:35:06 +0300
Subject: [PATCH 13/17] Update lightgbm_R.h

---
 R-package/src/lightgbm_R.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/R-package/src/lightgbm_R.h b/R-package/src/lightgbm_R.h
index d9fe51b32f96..41e2fbab13db 100644
--- a/R-package/src/lightgbm_R.h
+++ b/R-package/src/lightgbm_R.h
@@ -305,8 +305,7 @@ LIGHTGBM_C_EXPORT SEXP LGBM_BoosterGetNumClasses_R(
 /*!
 * \brief Get number of features.
 * \param handle Booster handle
-* \param out Total number of features
-* \return R NULL value
+* \return Total number of features, as R integer
 */
 LIGHTGBM_C_EXPORT SEXP LGBM_BoosterGetNumFeature_R(
   SEXP handle

From 44f21bec58be03e099d92b3f987e48958d08d2fd Mon Sep 17 00:00:00 2001
From: david-cortes <david.cortes.rivera@gmail.com>
Date: Tue, 26 Oct 2021 18:41:29 +0300
Subject: [PATCH 14/17] Update R-package/tests/testthat/test_lgb.Booster.R

Co-authored-by: James Lamb <jaylamb20@gmail.com>
---
 R-package/tests/testthat/test_lgb.Booster.R | 35 +++++++++++++++------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/R-package/tests/testthat/test_lgb.Booster.R b/R-package/tests/testthat/test_lgb.Booster.R
index a4eef52418bd..51cacfa81eab 100644
--- a/R-package/tests/testthat/test_lgb.Booster.R
+++ b/R-package/tests/testthat/test_lgb.Booster.R
@@ -1037,14 +1037,31 @@ test_that("boosters with linear models at leaves can be written to RDS and re-lo
 })
 
 test_that("Booster's print, show, and summary work correctly", {
-    check_methods_work <- function(model) {
-        expect_error(print(model), NA)
-        expect_error(show(model), NA)
-        expect_error(summary(model), NA)
+    .have_same_handle <- function(model, other_model){
+       expect_equal(
+         model$.__enclos_env__$private$handle
+         , other_model$.__enclos_env__$private$handle
+       )
+    }
+
+    .check_methods_work <- function(model) {
+      
+        # should work for fitted models
+        ret <- print(model)
+        .have_same_handle(ret, model)
+        ret <- show(model)
+        expect_null(ret)
+        ret <- summary(model)
+        .have_same_handle(ret, model)
+
+        # should not fail for finalized models
         model$finalize()
-        expect_error(print(model), NA)
-        expect_error(show(model), NA)
-        expect_error(summary(model), NA)
+        ret <- print(model)
+        .have_same_handle(ret, model)
+        ret <- show(model)
+        expect_null(ret)
+        ret <- summary(model)
+        .have_same_handle(ret, model)
     }
 
     data("mtcars")
@@ -1056,7 +1073,7 @@ test_that("Booster's print, show, and summary work correctly", {
         , verbose = 0L
         , nrounds = 5L
     )
-    check_methods_work(model)
+    .check_methods_work(model)
 
     data("iris")
     model <- lgb.train(
@@ -1068,7 +1085,7 @@ test_that("Booster's print, show, and summary work correctly", {
         , verbose = 0L
         , nrounds = 5L
     )
-    check_methods_work(model)
+    .check_methods_work(model)
 })
 
 test_that("LGBM_BoosterGetNumFeature_R returns correct outputs", {

From a2a125b33f5ccbca10a52ac9cd4486277b55dfa7 Mon Sep 17 00:00:00 2001
From: David Cortes <david.cortes.rivera@gmail.com>
Date: Tue, 26 Oct 2021 12:50:29 -0300
Subject: [PATCH 15/17] accommodate custom objectives in print

---
 R-package/R/lgb.Booster.R                   |  8 +++--
 R-package/tests/testthat/test_lgb.Booster.R | 34 +++++++++++++++++++++
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/R-package/R/lgb.Booster.R b/R-package/R/lgb.Booster.R
index 912769360d36..f4f5aaa4313a 100644
--- a/R-package/R/lgb.Booster.R
+++ b/R-package/R/lgb.Booster.R
@@ -834,11 +834,15 @@ print.lgb.Booster <- function(x, ...) {
   }
 
   if (!handle_is_null) {
+    obj <- x$params$objective
+    if (obj == "none") {
+      obj <- "custom"
+    }
     if (x$.__enclos_env__$private$num_class == 1L) {
-      cat(sprintf("Objective: %s\n", x$params$objective))
+      cat(sprintf("Objective: %s\n", obj))
     } else {
       cat(sprintf("Objective: %s (%d classes)\n"
-          , x$params$objective
+          , obj
           , x$.__enclos_env__$private$num_class))
     }
   } else {
diff --git a/R-package/tests/testthat/test_lgb.Booster.R b/R-package/tests/testthat/test_lgb.Booster.R
index 51cacfa81eab..c5b328c82973 100644
--- a/R-package/tests/testthat/test_lgb.Booster.R
+++ b/R-package/tests/testthat/test_lgb.Booster.R
@@ -1086,6 +1086,40 @@ test_that("Booster's print, show, and summary work correctly", {
         , nrounds = 5L
     )
     .check_methods_work(model)
+
+
+    # with custom objective
+    .logregobj <- function(preds, dtrain) {
+        labels <- get_field(dtrain, "label")
+        preds <- 1.0 / (1.0 + exp(-preds))
+        grad <- preds - labels
+        hess <- preds * (1.0 - preds)
+        return(list(grad = grad, hess = hess))
+    }
+
+    .evalerror <- function(preds, dtrain) {
+        labels <- get_field(dtrain, "label")
+        preds <- 1.0 / (1.0 + exp(-preds))
+        err <- as.numeric(sum(labels != (preds > 0.5))) / length(labels)
+        return(list(
+            name = "error"
+            , value = err
+            , higher_better = FALSE
+        ))
+    }
+
+    model <- lgb.train(
+        data = lgb.Dataset(
+            as.matrix(iris[, -5L])
+            , label = as.numeric(iris$Species == "virginica")
+        )
+        , obj = .logregobj
+        , eval = .evalerror
+        , verbose = 0L
+        , nrounds = 5L
+    )
+
+    .check_methods_work(model)
 })
 
 test_that("LGBM_BoosterGetNumFeature_R returns correct outputs", {

From f4334010a69dc9275f1e2efd07e0c1badd114bd4 Mon Sep 17 00:00:00 2001
From: David Cortes <david.cortes.rivera@gmail.com>
Date: Tue, 26 Oct 2021 12:55:15 -0300
Subject: [PATCH 16/17] linter

---
 R-package/tests/testthat/test_lgb.Booster.R | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/R-package/tests/testthat/test_lgb.Booster.R b/R-package/tests/testthat/test_lgb.Booster.R
index c5b328c82973..f42d3ff8cf1e 100644
--- a/R-package/tests/testthat/test_lgb.Booster.R
+++ b/R-package/tests/testthat/test_lgb.Booster.R
@@ -1037,7 +1037,7 @@ test_that("boosters with linear models at leaves can be written to RDS and re-lo
 })
 
 test_that("Booster's print, show, and summary work correctly", {
-    .have_same_handle <- function(model, other_model){
+    .have_same_handle <- function(model, other_model) {
        expect_equal(
          model$.__enclos_env__$private$handle
          , other_model$.__enclos_env__$private$handle

From c749482bea08c651c7bfaacb4641832448001c72 Mon Sep 17 00:00:00 2001
From: David Cortes <david.cortes.rivera@gmail.com>
Date: Tue, 26 Oct 2021 14:30:10 -0300
Subject: [PATCH 17/17] linter

---
 R-package/tests/testthat/test_lgb.Booster.R | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/R-package/tests/testthat/test_lgb.Booster.R b/R-package/tests/testthat/test_lgb.Booster.R
index f42d3ff8cf1e..8e4b417a035f 100644
--- a/R-package/tests/testthat/test_lgb.Booster.R
+++ b/R-package/tests/testthat/test_lgb.Booster.R
@@ -1045,7 +1045,7 @@ test_that("Booster's print, show, and summary work correctly", {
     }
 
     .check_methods_work <- function(model) {
-      
+
         # should work for fitted models
         ret <- print(model)
         .have_same_handle(ret, model)