Adding ability to load model from string in R (#472)

* Update lgb.Booster.R

Added method to call LGBM_BoosterLoadModelFromString_R if model_str is provided for initialization, added option to load from model_str in lgb.load

* Update lightgbm_R.cpp

Adding LGBM_BoosterLoadModelFromString_R

* Update lightgbm_R.cpp

Added LGBM_BoosterSaveModelToString_R

* Update lightgbm_R.cpp

* Update lgb.Booster.R

Added save_model_to_string method

* Update lgb.Booster.R

Implemented @Laurae2 comments

* Update lgb.Booster.R

* Update lightgbm_R.h

Added load and save model from/to string exports

R-package/R/lgb.Booster.R

@@ -24,6 +24,7 @@ Booster <- R6Class(
     initialize = function(params = list(),
                           train_set = NULL,
                           modelfile = NULL,
+                          model_str = NULL,
                           ...) {
       
       # Create parameters and handle
@@ -73,10 +74,22 @@ Booster <- R6Class(
                            ret = handle,
                            lgb.c_str(modelfile))
         
+      } else if (!is.null(model_str)) {
+        
+        # Do we have a model_str as character?
+          if (!is.character(model_str)) {
+            stop("lgb.Booster: Can only use a string as model_str")
+          }
+          
+          # Create booster from model
+          handle <- lgb.call("LGBM_BoosterLoadModelFromString_R",
+                             ret = handle,
+                             lgb.c_str(model_str))
+        
       } else {
         
         # Booster non existent
-        stop("lgb.Booster: Need at least either training dataset or model file to create booster instance")
+        stop("lgb.Booster: Need at least either training dataset, model file, or model_str to create booster instance")
         
       }
       
@@ -343,6 +356,21 @@ Booster <- R6Class(
       return(self)
     },
     
+    # Save model to string
+    save_model_to_string = function(num_iteration = NULL) {
+      
+      # Check if number of iteration is non existent
+      if (is.null(num_iteration)) {
+        num_iteration <- self$best_iter
+      }
+      
+      # Return model string
+      return(lgb.call.return.str("LGBM_BoosterSaveModelToString_R",
+                          private$handle,
+                          as.integer(num_iteration)))
+      
+    },
+    
     # Dump model in memory
     dump_model = function(num_iteration = NULL) {
       
@@ -645,9 +673,12 @@ predict.lgb.Booster <- function(object, data,
 
 #' Load LightGBM model
 #'
-#' Load LightGBM model from saved model file
+#' Load LightGBM model from saved model file or string
+#' Load LightGBM takes in either a file path or model string
+#' If both are provided, Load will default to loading from file
 #'
 #' @param filename path of model file
+#' @param model_str a str containing the model
 #'
 #' @return booster
 #' 
@@ -671,19 +702,32 @@ predict.lgb.Booster <- function(object, data,
 #'                    early_stopping_rounds = 10)
 #' lgb.save(model, "model.txt")
 #' load_booster <- lgb.load("model.txt")
+#' load_booster_from_str <- lgb.load(model$raw)
 #' }
 #' 
 #' @rdname lgb.load
 #' @export
-lgb.load <- function(filename){
+lgb.load <- function(filename = NULL, model_str = NULL){
   
-  # Check if file name is character or not
-  if (!is.character(filename)) {
+  if (is.null(filename) && is.null(model_str)) {
+    stop("lgb.load: either filename or model_str must be given")
+  }
+  
+  # Load from filename
+  if (!is.null(filename) && !is.character(filename)) {
     stop("lgb.load: filename should be character")
   }
   
   # Return new booster
-  Booster$new(modelfile = filename)
+  if (!is.null(filename) && !file.exists(filename)) stop("lgb.load: file does not exist for supplied filename")
+  if (!is.null(filename)) return(Booster$new(modelfile = filename))
+  
+  # Load from model_str
+  if (!is.null(model_str) && !is.character(model_str)) {
+    stop("lgb.load: model_str should be character")
+  }    
+  # Return new booster
+  if (!is.null(model_str)) return(Booster$new(model_str = model_str))
   
 }
 

R-package/src/lightgbm_R.cpp

@@ -324,6 +324,18 @@ LGBM_SE LGBM_BoosterCreateFromModelfile_R(LGBM_SE filename,
   R_API_END();
 }
 
+LGBM_SE LGBM_BoosterLoadModelFromString_R(LGBM_SE model_str,
+  LGBM_SE out,
+  LGBM_SE call_state) {
+
+  R_API_BEGIN();
+  int out_num_iterations = 0;
+  BoosterHandle handle;
+  CHECK_CALL(LGBM_BoosterLoadModelFromString(R_CHAR_PTR(model_str), &out_num_iterations, &handle));
+  R_SET_PTR(out, handle);
+  R_API_END();
+}
+
 LGBM_SE LGBM_BoosterMerge_R(LGBM_SE handle,
   LGBM_SE other_handle,
   LGBM_SE call_state) {
@@ -579,6 +591,25 @@ LGBM_SE LGBM_BoosterSaveModel_R(LGBM_SE handle,
   R_API_END();
 }
 
+LGBM_SE LGBM_BoosterSaveModelToString_R(LGBM_SE handle,
+  LGBM_SE num_iteration,
+  LGBM_SE buffer_len,
+  LGBM_SE actual_len,
+  LGBM_SE out_str,
+  LGBM_SE call_state) {
+  R_API_BEGIN();
+  int out_len = 0;
+  std::vector<char> inner_char_buf(R_AS_INT(buffer_len));
+  CHECK_CALL(LGBM_BoosterSaveModelToString(R_GET_PTR(handle), R_AS_INT(num_iteration), R_AS_INT(buffer_len), &out_len, inner_char_buf.data()));
+  EncodeChar(out_str, inner_char_buf.data(), buffer_len, actual_len);
+  if (out_len < R_AS_INT(buffer_len)) {
+    EncodeChar(out_str, inner_char_buf.data(), buffer_len, actual_len);
+  } else {
+    R_INT_PTR(actual_len)[0] = static_cast<int>(out_len);
+  }
+  R_API_END();
+}
+
 LGBM_SE LGBM_BoosterDumpModel_R(LGBM_SE handle,
   LGBM_SE num_iteration,
   LGBM_SE buffer_len,

R-package/src/lightgbm_R.h

@@ -224,6 +224,16 @@ LIGHTGBM_C_EXPORT LGBM_SE LGBM_BoosterCreateFromModelfile_R(LGBM_SE filename,
   LGBM_SE out,
   LGBM_SE call_state);
 
+/*!
+* \brief load an existing boosting from model_str
+* \param model_str string containing the model
+* \param out handle of created Booster
+* \return 0 when succeed, -1 when failure happens
+*/
+LIGHTGBM_C_EXPORT LGBM_SE LGBM_BoosterLoadModelFromString_R(LGBM_SE model_str,
+  LGBM_SE out,
+  LGBM_SE call_state);
+  
 /*!
 * \brief Merge model in two boosters to first handle
 * \param handle handle, will merge other handle to this
@@ -468,6 +478,20 @@ LIGHTGBM_C_EXPORT LGBM_SE LGBM_BoosterSaveModel_R(LGBM_SE handle,
   LGBM_SE filename,
   LGBM_SE call_state);
 
+/*!
+* \brief create string containing model
+* \param handle handle
+* \param num_iteration, <= 0 means save all
+* \param out_str string of model
+* \return 0 when succeed, -1 when failure happens
+*/
+LIGHTGBM_C_EXPORT LGBM_SE LGBM_BoosterSaveModelToString_R(LGBM_SE handle,
+  LGBM_SE num_iteration,
+  LGBM_SE buffer_len,
+  LGBM_SE actual_len,
+  LGBM_SE out_str,
+  LGBM_SE call_state);
+
 /*!
 * \brief dump model to json
 * \param handle handle