improved docs

pyterrier/apply.py

@@ -172,12 +172,12 @@ def generic(fn : Union[Callable[[pd.DataFrame], pd.DataFrame], Callable[[pt.mode
     """
         Create a transformer that changes the input dataframe to another dataframe in an unspecified way.
 
-        The supplied function is called once for an entire result set as a dataframe (which may contain one of more queries).
-        Each time it should return a new dataframe. The returned dataframe should abide by the general PyTerrier Data Model,
-        for instance updating the rank column if the scores are amended.
+        The supplied function is called once for an entire result set as a dataframe or iter-dict (which may contain one or 
+        more queries and one or more documents). Each time it should return a new dataframe. The returned dataframe (or yielded row) 
+        should abide by the general PyTerrier Data Model, for instance updating the rank column if the scores are amended.
 
         Arguments:
-            fn(Callable): the function to apply to each row
+            fn(Callable): the function to apply to each result set
             batch_size(int or None): whether to apply fn on batches of rows or all that are received
             verbose(bool): Whether to display a progress bar over batches (only used if batch_size is set, and iter is not set).
             iter(bool): Whether to use the iter-dict API - if-so, then ``fn`` receives an iterable, and returns an iterable.