fix: restore numeric-vector-requires-y guard in cor/covDS

Server-side check preserves pre-refactor contract that was dropped
when client-side validation moved to server. Redocument levelsDS.

Author: timcadman

R/corDS.R

@@ -38,7 +38,11 @@ corDS <- function(x=NULL, y=NULL){
   else{
     y.val <- NULL
   }
-  
+
+  if (is.null(y.val) && any(class(x.val) %in% c("numeric", "integer"))) {
+    stop("If x is a numeric vector, y must also be a numeric vector.", call. = FALSE)
+  }
+
   # create a data frame for the variables
   if (is.null(y.val)){
     dataframe <- as.data.frame(x.val)

R/covDS.R

@@ -47,7 +47,11 @@ covDS <- function(x=NULL, y=NULL, use=NULL){
   else{
     y.val <- NULL
   }
-  
+
+  if (is.null(y.val) && any(class(x.val) %in% c("numeric", "integer"))) {
+    stop("If x is a numeric vector, y must also be a numeric vector.", call. = FALSE)
+  }
+
   # create a data frame for the variables
   if (is.null(y.val)){
     dataframe <- as.data.frame(x.val)