_iterator_weight should not sort objects

Author: jdemeyer

src/sage/combinat/multiset_partition_into_sets_ordered.py

@@ -2769,6 +2769,7 @@ def _base_iterator(constraints):
     # else
     return None
 
+
 def _iterator_weight(weight):
     """
     An iterator for the ordered multiset partitions into sets with weight given by
@@ -2807,33 +2808,28 @@ def _iterator_weight(weight):
          (frozenset({1}), frozenset({3}), frozenset({1})),
          (frozenset({1, 3}), frozenset({1})),
          (frozenset({3}), frozenset({1}), frozenset({1}))]
+        sage: list(_iterator_weight([]))
+        [()]
     """
+    # "weight" should be a dict mapping keys to weights
     if isinstance(weight, (list, tuple)):
-        weight = {k+1: val for k,val in enumerate(weight) if val > 0}
-    if isinstance(weight, dict):
-        multiset = tuple([k for k in sorted(weight) for _ in range(weight[k])])
+        weight = {k+1: val for k, val in enumerate(weight) if val}
+
+    # We first map the arbitrary keys to integers to combat unreliable
+    # sorting behavior.
+    keys = tuple(set(weight))
+    multiset = []
+    for i, key in enumerate(keys):
+        multiset += [i] * weight[key]
+
+    # We build ordered multiset partitions into sets of `X` by
+    # permutation + deconcatenation
+    for alpha in Permutations_mset(multiset):
+        co = _break_at_descents(alpha, weak=True)
+        for A in OrderedMultisetPartitionIntoSets(co).finer(strong=True):
+            B = tuple([frozenset([keys[i] for i in block]) for block in A])
+            yield B
 
-    if not multiset:
-        yield ()
-    else:
-        # We build ordered multiset partitions into sets of `X` by permutation + deconcatenation
-        # We first standardize the multiset to combat unreliable sorting behavior.
-        em = enumerate(set(multiset))
-        key_to_indx = {}
-        indx_to_key = {}
-        for (i,key) in em:
-            key_to_indx[key] = i
-            indx_to_key[i] = key
-        std_multiset = []
-        for a in multiset:
-            std_multiset.append(key_to_indx[a])
-        std_multiset = sorted(std_multiset)
-
-        for alpha in Permutations_mset(std_multiset):
-            co = _break_at_descents(alpha, weak=True)
-            for A in OrderedMultisetPartitionIntoSets(co).finer(strong=True):
-                B = tuple([frozenset([indx_to_key[i] for i in block]) for block in A])
-                yield B
 
 def _iterator_size(size, length=None, alphabet=None):
     r"""