Ticket #13236: trac_13236-iterator_of_homogeneous_component_of_ranked_poset-nu.patch

sage/combinat/posets/posets.py

@@ -1919 +1919 @@
         """
         return [x for x in self.lower_covers_iterator(y)]
 
+    def elements_of_the_rank_iterator(self,k):
+        r"""
+        Rertuns an iterator of the elements of rank k.
+        
+        INPUT: ``k``: an integer
+    
+        OUTPUT: an iterator of the elements of rank k.
+
+        Examples::
+
+            sage: type(Poset(([0,1,2],[(0,1),(0,2)])).elements_of_the_rank_iterator(1))
+            <type 'generator'>
+        
+            sage: list(Poset(([0,1,2,3,4],[(0,1),(1,4),(0,2),(2,3),(3,4)])).elements_of_the_rank_iterator(1))
+            Traceback (most recent call last):
+            ...
+            ValueError: Poset is not ranked
+
+        """
+        p = self
+        r = p.rank_function()
+        if p.is_ranked():
+            for a in p:
+                if r(a) == k:
+                    yield a
+        else:
+            raise ValueError, "Poset is not ranked"
+
+    def elements_of_the_rank(self,k):
+        r"""
+        Rertuns the list of the elements of rank k.
+        
+        INPUT: ``k``: an integer
+    
+        OUTPUT: a list of the elements of rank k.
+
+        Examples::
+
+            sage: Poset(([0,1,2],[(0,1),(0,2)])).elements_of_the_rank(1)
+            [1, 2]
+        
+            sage: Poset(([0,1,2,3,4],[(0,1),(1,4),(0,2),(2,3),(3,4)])).elements_of_the_rank(1)
+            Traceback (most recent call last):
+            ...
+            ValueError: Poset is not ranked
+
+        """
+        return [ a for a in self.elements_of_the_rank_iterator(k) ]
+
     def cardinality(self):
         """
         Returns the number of elements in the poset.