[R] fix uses of 1:length(x) and other small things (#5992)

R-package/R/xgb.DMatrix.R

@@ -357,7 +357,7 @@ slice.xgb.DMatrix <- function(object, idxset, ...) {
 #' @export
 print.xgb.DMatrix <- function(x, verbose = FALSE, ...) {
   cat('xgb.DMatrix  dim:', nrow(x), 'x', ncol(x), ' info: ')
-  infos <- c()
+  infos <- character(0)
   if (length(getinfo(x, 'label')) > 0) infos <- 'label'
   if (length(getinfo(x, 'weight')) > 0) infos <- c(infos, 'weight')
   if (length(getinfo(x, 'base_margin')) > 0) infos <- c(infos, 'base_margin')

R-package/R/xgb.plot.importance.R

@@ -106,12 +106,12 @@ xgb.plot.importance <- function(importance_matrix = NULL, top_n = NULL, measure
     par(mar = mar)
 
     # reverse the order of rows to have the highest ranked at the top
-    importance_matrix[nrow(importance_matrix):1,
+    importance_matrix[rev(seq_len(nrow(importance_matrix))),
                       barplot(Importance, horiz = TRUE, border = NA, cex.names = cex,
                               names.arg = Feature, las = 1, ...)]
     grid(NULL, NA)
     # redraw over the grid
-    importance_matrix[nrow(importance_matrix):1,
+    importance_matrix[rev(seq_len(nrow(importance_matrix))),
                       barplot(Importance, horiz = TRUE, border = NA, add = TRUE)]
     par(op)
   }

R-package/R/xgb.plot.shap.R

@@ -124,7 +124,7 @@ xgb.plot.shap <- function(data, shap_contrib = NULL, features = NULL, top_n = 1,
     stop("shap_contrib is not compatible with the provided data")
 
   nsample <- if (is.null(subsample)) min(100000, nrow(data)) else as.integer(subsample * nrow(data))
-  idx <- sample(1:nrow(data), nsample)
+  idx <- sample(seq_len(nrow(data)), nsample)
   data <- data[idx, ]
 
   if (is.null(shap_contrib)) {
@@ -162,7 +162,7 @@ xgb.plot.shap <- function(data, shap_contrib = NULL, features = NULL, top_n = 1,
   data <- data[, features, drop = FALSE]
   cols <- colnames(data)
   if (is.null(cols)) cols <- colnames(shap_contrib)
-  if (is.null(cols)) cols <- paste0('X', 1:ncol(data))
+  if (is.null(cols)) cols <- paste0('X', seq_len(ncol(data)))
   colnames(data) <- cols
   colnames(shap_contrib) <- cols