sort: add reverse argument

rxsci/data/sort.py

@@ -4,27 +4,30 @@
 import rxsci as rs
 
 
-def sort(key=lambda i: i):
+def sort(key=lambda i: i, reverse=False):
     '''sort items according to key
 
-    Items are sorted in ascending order.
+    Items are sorted in ascending order by default. When reverse is set to
+    True, they are sorted by descending order.
 
     Impementation note: This operator caches all the items of the source
-    observable before sorting them. It can be used ONLY on BATCH source, and
-    consumes a lot of memory.
+    observable before sorting them. Si, it can be used only on a batch source,
+    and can lead to high memory usage.
 
     The source must be an Observable.
 
     Args:
         key: [Optional] function used to extract the sorting key on each item.
+        reverse: [Optional] Set to True for descendig sorting.
+
 
     Returns:
         An observable emitting the sorted items of the source observable.
     '''
     def _sort(source):
         return source.pipe(
             rs.data.to_list(),
-            rs.ops.map(lambda i: sorted(i, key=key)),
+            rs.ops.map(lambda i: sorted(i, key=key, reverse=reverse)),
             rs.data.to_deque(extend=True),
         )
 

rxsci/operators/pandas.py

@@ -49,7 +49,7 @@ def to_pandas(columns=None):
         The source must be an Observable.
 
         Args:
-            columns: [Optional]
+            columns: [Optional] The name of the columns of the dataframe
 
         Returns:
             An observable the emits a single item. This item is a pandas

tests/data/test_sort.py

@@ -15,6 +15,18 @@ def test_sort():
     assert actual_result == expected_result
 
 
+def test_sort_reverse():
+    source = [2, 3, 10, 4, 1, 5, 6, 7, 5, 9, 8, 9, 11, 11]
+    expected_result = [11, 11, 10, 9, 9, 8, 7, 6, 5, 5, 4, 3, 2, 1]
+    actual_result = []
+
+    rx.from_(source).pipe(
+        rs.data.sort(reverse=True)
+    ).subscribe(on_next=actual_result.append)
+
+    assert actual_result == expected_result
+
+
 def test_sort_key():
     source = [2, 3, 10, 4, 1, 5, 6, 7, 5, 9, 8, 9, 11, 11]
     expected_result = [11, 11, 10, 9, 9, 8, 7, 6, 5, 5, 4, 3, 2, 1]