fix: Using if() conditions comparing class() to string

Now using inherits()

R/var.relations.R

@@ -91,7 +91,7 @@ var.relations = function(x = NULL, y = NULL, num.trees = 500, type = "regression
         stop("Too much classes defined, classification might be the wrong choice")
       }
     }
-    if (type == "regression" && class(y) == "factor") {
+    if (type == "regression" && inherits(y, "factor")) {
       stop("use factor variable for y only for classification! ")
     }
 

R/var.relations.mfi.R

@@ -93,7 +93,7 @@ var.relations.mfi = function(x = NULL, y = NULL, num.trees = 500, type = "regres
         stop("Too much classes defined, classification might be the wrong choice")
       }
     }
-    if (type == "regression" && class(y) == "factor") {
+    if (type == "regression" && inherits(y, "factor")) {
       stop("use factor variable for y only for classification! ")
     }
 

R/variable_selection_mir.R

@@ -110,7 +110,7 @@ var.select.mir = function(x = NULL, y = NULL, num.trees = 500, type = "regressio
         stop("Too much classes defined, classification might be the wrong choice")
       }
     }
-    if (type == "regression" && class(y) == "factor") {
+    if (type == "regression" && inherits(y, "factor")) {
       stop("use factor variable for y only for classification! ")
     }
 

R/variable_selection_smd.R

@@ -112,7 +112,7 @@ var.select.smd = function(x = NULL, y = NULL, num.trees = 500, type = "regressio
       stop("Too much classes defined, classification might be the wrong choice")
     }
   }
-  if (type == "regression" && class(y) == "factor") {
+  if (type == "regression" && inherits(y, "factor")) {
     stop("use factor variable for y only for classification! ")
   }
   data = data.frame(y, x)