add slice document

R-package/NAMESPACE

@@ -1,6 +1,7 @@
 # Generated by roxygen2 (4.0.1): do not edit by hand
 
 export(getinfo)
+export(slice)
 export(xgb.DMatrix)
 export(xgb.DMatrix.save)
 export(xgb.dump)

R-package/R/slice.xgb.DMatrix.R

@@ -0,0 +1,30 @@
+setClass('xgb.DMatrix')
+
+#' Get a new DMatrix containing the specified rows of
+#' orginal xgb.DMatrix object
+#'
+#' Get a new DMatrix containing the specified rows of
+#' orginal xgb.DMatrix object
+#' 
+#' @param object Object of class "xgb.DMatrix"
+#' @param idxset a integer vector of indices of rows needed
+#' 
+#' @examples
+#' data(iris)
+#' iris[,5] <- as.numeric(iris[,5])
+#' dtrain <- xgb.DMatrix(as.matrix(iris[,1:4]), label=iris[,5])
+#' dsub <- slice(dtrain, c(1,2,3))
+#' @export
+#' 
+slice <- function(object, ...){
+    UseMethod("slice")
+}
+
+setMethod("slice", signature = "xgb.DMatrix", 
+          definition = function(object, idxset) {
+              if (class(object) != "xgb.DMatrix") {
+                  stop("slice: first argument dtrain must be xgb.DMatrix")
+              }
+              ret <- .Call("XGDMatrixSliceDMatrix_R", object, idxset, PACKAGE = "xgboost")
+              return(structure(ret, class = "xgb.DMatrix"))
+          })

R-package/man/slice.Rd

@@ -0,0 +1,24 @@
+% Generated by roxygen2 (4.0.1): do not edit by hand
+\name{slice}
+\alias{slice}
+\title{Get a new DMatrix containing the specified rows of
+orginal xgb.DMatrix object}
+\usage{
+slice(object, ...)
+}
+\arguments{
+\item{object}{Object of class "xgb.DMatrix"}
+
+\item{idxset}{a integer vector of indices of rows needed}
+}
+\description{
+Get a new DMatrix containing the specified rows of
+orginal xgb.DMatrix object
+}
+\examples{
+data(iris)
+iris[,5] <- as.numeric(iris[,5])
+dtrain <- xgb.DMatrix(as.matrix(iris[,1:4]), label=iris[,5])
+dsub <- slice(dtrain, c(1,2,3))
+}
+

R-package/src/xgboost_R.cpp

@@ -91,6 +91,18 @@ extern "C" {
     UNPROTECT(1);
     return ret;
   }
+  SEXP XGDMatrixSliceDMatrix_R(SEXP handle, SEXP idxset) {
+    int len = length(idxset);
+    std::vector<int> idxvec(len);
+    for (int i = 0; i < len; ++i) {
+      idxvec[i] = INTEGER(idxset)[i] - 1;
+    }
+    void *res = XGDMatrixSliceDMatrix(R_ExternalPtrAddr(handle),  &idxvec[0], len);
+    SEXP ret = PROTECT(R_MakeExternalPtr(res, R_NilValue, R_NilValue));
+    R_RegisterCFinalizerEx(ret, _DMatrixFinalizer, TRUE);
+    UNPROTECT(1);
+    return ret;        
+  }
   void XGDMatrixSaveBinary_R(SEXP handle, SEXP fname, SEXP silent) {
     XGDMatrixSaveBinary(R_ExternalPtrAddr(handle),
                         CHAR(asChar(fname)), asInteger(silent));

R-package/src/xgboost_R.h

@@ -36,6 +36,13 @@ extern "C" {
   SEXP XGDMatrixCreateFromCSC_R(SEXP indptr,
                                 SEXP indices,
                                 SEXP data);
+  /*!
+   * \brief create a new dmatrix from sliced content of existing matrix
+   * \param handle instance of data matrix to be sliced
+   * \param idxset index set
+   * \return a sliced new matrix
+   */
+  SEXP XGDMatrixSliceDMatrix_R(SEXP handle, SEXP idxset);
   /*!
    * \brief load a data matrix into binary file
    * \param handle a instance of data matrix