DEPR: DataFrame.lookup

doc/source/whatsnew/v1.1.0.rst

@@ -824,6 +824,7 @@ Deprecations
   precision through the ``rtol``, and ``atol`` parameters, thus deprecating the
   ``check_less_precise`` parameter. (:issue:`13357`).
 - :func:`DataFrame.melt` accepting a value_name that already exists is deprecated, and will be removed in a future version (:issue:`34731`)
+- :meth:`DataFrame.lookup` is deprecated and will be removed in a future version, use :meth:`DataFrame.melt` and :meth:`DataFrame.loc` instead (:issue:`18682`)
 
 .. ---------------------------------------------------------------------------
 

pandas/core/frame.py

@@ -3772,6 +3772,11 @@ def lookup(self, row_labels, col_labels) -> np.ndarray:
         Given equal-length arrays of row and column labels, return an
         array of the values corresponding to each (row, col) pair.
 
+        .. deprecated:: 1.1.0
+
+        DataFrame.lookup is deprecated,
+        use DataFrame.melt and DataFrame.loc instead.
+
         Parameters
         ----------
         row_labels : sequence
@@ -3784,6 +3789,12 @@ def lookup(self, row_labels, col_labels) -> np.ndarray:
         numpy.ndarray
             The found values.
         """
+        msg = (
+            "The 'lookup' method is deprecated and will be"
+            "removed in a future version."
+        )
+        warnings.warn(msg, FutureWarning, stacklevel=2)
+
         n = len(row_labels)
         if n != len(col_labels):
             raise ValueError("Row labels must have same size as column labels")

pandas/tests/frame/indexing/test_indexing.py

@@ -2229,3 +2229,12 @@ def test_object_casting_indexing_wraps_datetimelike():
     assert blk.dtype == "m8[ns]"  # we got the right block
     val = blk.iget((0, 0))
     assert isinstance(val, pd.Timedelta)
+
+
+def test_lookup_deprecated():
+    # GH18262
+    df = pd.DataFrame(
+        {"col": ["A", "A", "B", "B"], "A": [80, 23, np.nan, 22], "B": [80, 55, 76, 67]}
+    )
+    with tm.assert_produces_warning(FutureWarning):
+        df.lookup(df.index, df["col"])