diff --git a/pina/geometry/cartesian.py b/pina/geometry/cartesian.py
index ef1a6fe9..11354b62 100644
--- a/pina/geometry/cartesian.py
+++ b/pina/geometry/cartesian.py
@@ -232,16 +232,18 @@ def _single_points_sample(n, variables):
 
             return result
 
+        if variables == "all":
+            variables = self.variables
+        elif isinstance(variables, (list, tuple)):
+            variables = sorted(variables)
+
         if self.fixed_ and (not self.range_):
             return _single_points_sample(n, variables)
 
-        if variables == "all":
-            variables = list(self.range_.keys()) + list(self.fixed_.keys())
-
         if mode in ["grid", "chebyshev"]:
-            return _1d_sampler(n, mode, variables)
+            return _1d_sampler(n, mode, variables).extract(variables)
         elif mode in ["random", "lh", "latin"]:
-            return _Nd_sampler(n, mode, variables)
+            return _Nd_sampler(n, mode, variables).extract(variables)
         else:
             raise ValueError(f"mode={mode} is not valid.")
 
diff --git a/pina/geometry/ellipsoid.py b/pina/geometry/ellipsoid.py
index e809bf6c..2baea532 100644
--- a/pina/geometry/ellipsoid.py
+++ b/pina/geometry/ellipsoid.py
@@ -275,13 +275,18 @@ def _single_points_sample(n, variables):
 
             return result
 
+        if variables == "all":
+            variables = self.variables
+        elif isinstance(variables, (list, tuple)):
+            variables = sorted(variables)
+
         if self.fixed_ and (not self.range_):
-            return _single_points_sample(n, variables)
+            return _single_points_sample(n, variables).extract(variables)
 
         if variables == "all":
             variables = self.variables
 
         if mode in ["random"]:
-            return _Nd_sampler(n, mode, variables)
+            return _Nd_sampler(n, mode, variables).extract(variables)
         else:
             raise NotImplementedError(f"mode={mode} is not implemented.")
diff --git a/pina/geometry/simplex.py b/pina/geometry/simplex.py
index 8a604b79..4f2e3623 100644
--- a/pina/geometry/simplex.py
+++ b/pina/geometry/simplex.py
@@ -231,11 +231,17 @@ def sample(self, n, mode="random", variables="all"):
             in ``variables``.
         """
 
+        if variables == "all":
+            variables = self.variables
+        elif isinstance(variables, (list, tuple)):
+            variables = sorted(variables)
+
         if mode in ["random"]:
             if self._sample_surface:
                 sample_pts = self._sample_boundary_randomly(n)
             else:
-                sample_pts = self._sample_interior_randomly(n, variables)
+                sample_pts = self._sample_interior_randomly(n, variables
+                                                            )
 
         else:
             raise NotImplementedError(f"mode={mode} is not implemented.")