add slice document

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"))
+          })