new nrow function for xgb.DMatrix

R-package/R/nrow.xgb.DMatrix.R

@@ -0,0 +1,18 @@
+setGeneric("nrow")
+
+#' @param x Object of class \code{xgb.DMatrix}
+#' @title \code{nrow} return the number of rows present in x.
+#' @rdname nrow
+#' @examples
+#' data(agaricus.train, package='xgboost')
+#' train <- agaricus.train
+#' dtrain <- xgb.DMatrix(train$data, label=train$label)
+#' stopifnot(nrow(dtrain) == nrow(train$data))
+#' 
+#' @export
+setMethod("nrow",
+          signature = "xgb.DMatrix",
+          definition = function(x) {
+            xgb.numrow(x)
+          }
+)