docs: Clarify the join pre-condition of join_asof (#20509)

pola-rs · Dec 31, 2024 · a569b7d · a569b7d
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diff --git a/py-polars/polars/dataframe/frame.py b/py-polars/polars/dataframe/frame.py
@@ -6940,7 +6940,8 @@ def join_asof(
         This is similar to a left-join except that we match on nearest key rather than
         equal keys.
 
-        Both DataFrames must be sorted by the asof_join key.
+        Both DataFrames must be sorted by the `on` key (within each `by` group, if
+        specified).
 
         For each row in the left DataFrame:
 

diff --git a/py-polars/polars/lazyframe/frame.py b/py-polars/polars/lazyframe/frame.py
@@ -4274,7 +4274,8 @@ def join_asof(
         This is similar to a left-join except that we match on nearest key rather than
         equal keys.
 
-        Both DataFrames must be sorted by the join_asof key.
+        Both DataFrames must be sorted by the `on` key (within each `by` group, if
+        specified).
 
         For each row in the left DataFrame: