factorized a unique_multi helper function

it computes unique values across multiple iterables

Author: gdementen

larray/core/array.py

@@ -8469,10 +8469,7 @@ def stack(elements=None, axis=None, title=None, meta=None, dtype=None, **kwargs)
         if not all(isinstance(s, Session) for s in sessions):
             raise TypeError("stack() only supports stacking Session with other Session objects")
 
-        seen = set()
-        all_keys = []
-        for s in sessions:
-            unique_list(s.keys(), all_keys, seen)
+        all_keys = unique_multi(s.keys() for s in sessions)
         res = []
         for name in all_keys:
             try:

larray/core/axis.py

@@ -16,7 +16,7 @@
                                _range_to_slice, _seq_group_to_name, _translate_group_key_hdf, remove_nested_groups)
 from larray.util.oset import *
 from larray.util.misc import (basestring, PY2, unicode, long, duplicates, array_lookup2, ReprString, index_by_id,
-                              renamed_to, common_type, LHDFStore, lazy_attribute, _isnoneslice)
+                              renamed_to, common_type, LHDFStore, lazy_attribute, _isnoneslice, unique_multi)
 
 
 class Axis(ABCAxis):
@@ -1163,11 +1163,7 @@ def union(self, other):
             other = _to_ticks(other, parse_single_int=True) if '..' in other or ',' in other else [other]
         if isinstance(other, Axis):
             other = other.labels
-        unique_labels = []
-        seen = set()
-        unique_list(self.labels, unique_labels, seen)
-        unique_list(other, unique_labels, seen)
-        return Axis(unique_labels, self.name)
+        return Axis(unique_multi((self.labels, other)), self.name)
 
     def intersection(self, other):
         """Returns axis with the (set) intersection of this axis labels and other labels.

larray/util/misc.py

@@ -236,6 +236,17 @@ def unique_list(iterable, res=None, seen=None):
     return res
 
 
+def unique_multi(iterable_of_iterables):
+    """
+    Returns a list of all unique elements across multiple iterables. Elements of earlier iterables will come first.
+    """
+    seen = set()
+    res = []
+    for iterable in iterable_of_iterables:
+        unique_list(iterable, res, seen)
+    return res
+
+
 def duplicates(iterable):
     """
     List duplicated elements once, preserving order. Remember all elements ever seen.