add header to match keystyle

Author: Mukulyadav2004

R/print.data.table.R

@@ -63,14 +63,23 @@ print.data.table = function(x, topn=getOption("datatable.print.topn"),
     return(invisible(x))
   }
   if (show.indices) {
-    if (is.null(indices(x))) {
-      show.indices = FALSE
-    } else {
-      index_dt <- as.data.table(attributes(attr(x, 'index')))
-      print_names <- paste0("index", if (ncol(index_dt) > 1L) seq_len(ncol(index_dt)) else "", ":", sub("^__", "", names(index_dt)))
-      setnames(index_dt, print_names)
+   indices <- names(attr(x, "index", exact = TRUE))  # Get actual index names
+    if (length(indices)) {
+      # Clean index formatting
+      cleaned_indices <- gsub("^__|_", ", ", indices)
+      cleaned_indices <- sub(", $", "", cleaned_indices)  
+      # Create header string (matches key display style)
+      header <- paste0("Indices: ", paste(cleaned_indices, collapse = ", "))
+
+    # Add to existing header metadata instead of toprint
+    if (exists("header", envir = parent.frame(), inherits = FALSE)) {
+      assign("header", c(get("header", envir = parent.frame()), header), 
+             envir = parent.frame())
     }
   }
+  else {
+    show.indices <- FALSE  
+}
   n_x = nrow(x)
   if ((topn*2L+1L)<n_x && (n_x>nrows || !topnmiss)) {
     toprint = rbindlist(list(head(x, topn), tail(x, topn)), use.names=FALSE)  # no need to match names because head and tail of same x, and #3306