From 5949f0d01163144b2e3dee0dff11894d879058ce Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Tue, 5 Aug 2025 09:27:27 -0700
Subject: [PATCH] REF: simplify mask_missing

---
 pandas/core/dtypes/common.py |  8 ++--
 pandas/core/missing.py       | 72 +++++++++++++-----------------------
 2 files changed, 30 insertions(+), 50 deletions(-)

diff --git a/pandas/core/dtypes/common.py b/pandas/core/dtypes/common.py
index 68d99937f728c..99415b6fc6ec8 100644
--- a/pandas/core/dtypes/common.py
+++ b/pandas/core/dtypes/common.py
@@ -1168,10 +1168,10 @@ def is_numeric_v_string_like(a: ArrayLike, b) -> bool:
     is_a_array = isinstance(a, np.ndarray)
     is_b_array = isinstance(b, np.ndarray)
 
-    is_a_numeric_array = is_a_array and a.dtype.kind in ("u", "i", "f", "c", "b")
-    is_b_numeric_array = is_b_array and b.dtype.kind in ("u", "i", "f", "c", "b")
-    is_a_string_array = is_a_array and a.dtype.kind in ("S", "U")
-    is_b_string_array = is_b_array and b.dtype.kind in ("S", "U")
+    is_a_numeric_array = is_a_array and a.dtype.kind in "uifcb"
+    is_b_numeric_array = is_b_array and b.dtype.kind in "uifcb"
+    is_a_string_array = is_a_array and a.dtype.kind in "SU"
+    is_b_string_array = is_b_array and b.dtype.kind in "SU"
 
     is_b_scalar_string_like = not is_b_array and isinstance(b, str)
 
diff --git a/pandas/core/missing.py b/pandas/core/missing.py
index 66609fa870f14..b443b22201e37 100644
--- a/pandas/core/missing.py
+++ b/pandas/core/missing.py
@@ -34,7 +34,6 @@
     is_array_like,
     is_bool_dtype,
     is_numeric_dtype,
-    is_numeric_v_string_like,
     is_object_dtype,
     needs_i8_conversion,
 )
@@ -64,75 +63,56 @@ def check_value_size(value, mask: npt.NDArray[np.bool_], length: int):
     return value
 
 
-def mask_missing(arr: ArrayLike, values_to_mask) -> npt.NDArray[np.bool_]:
+def mask_missing(arr: ArrayLike, value) -> npt.NDArray[np.bool_]:
     """
     Return a masking array of same size/shape as arr
-    with entries equaling any member of values_to_mask set to True
+    with entries equaling value set to True.
 
     Parameters
     ----------
     arr : ArrayLike
-    values_to_mask: list, tuple, or scalar
+    value : scalar-like
+        Caller has ensured `not is_list_like(value)` and that it can be held
+        by `arr`.
 
     Returns
     -------
     np.ndarray[bool]
     """
-    # When called from Block.replace/replace_list, values_to_mask is a scalar
-    #  known to be holdable by arr.
-    # When called from Series._single_replace, values_to_mask is tuple or list
-    dtype, values_to_mask = infer_dtype_from(values_to_mask)
+    dtype, value = infer_dtype_from(value)
 
-    if isinstance(dtype, np.dtype):
-        values_to_mask = np.array(values_to_mask, dtype=dtype)
-    else:
-        cls = dtype.construct_array_type()
-        if not lib.is_list_like(values_to_mask):
-            values_to_mask = [values_to_mask]
-        values_to_mask = cls._from_sequence(values_to_mask, dtype=dtype, copy=False)
-
-    potential_na = False
-    if is_object_dtype(arr.dtype):
-        # pre-compute mask to avoid comparison to NA
-        potential_na = True
-        arr_mask = ~isna(arr)
-
-    na_mask = isna(values_to_mask)
-    nonna = values_to_mask[~na_mask]
+    if isna(value):
+        return isna(arr)
 
     # GH 21977
     mask = np.zeros(arr.shape, dtype=bool)
     if (
         is_numeric_dtype(arr.dtype)
         and not is_bool_dtype(arr.dtype)
-        and is_bool_dtype(nonna.dtype)
+        and lib.is_bool(value)
     ):
+        # e.g. test_replace_ea_float_with_bool, see GH#62048
         pass
     elif (
-        is_bool_dtype(arr.dtype)
-        and is_numeric_dtype(nonna.dtype)
-        and not is_bool_dtype(nonna.dtype)
+        is_bool_dtype(arr.dtype) and is_numeric_dtype(dtype) and not lib.is_bool(value)
     ):
+        # e.g. test_replace_ea_float_with_bool, see GH#62048
         pass
+    elif is_numeric_dtype(arr.dtype) and isinstance(value, str):
+        # GH#29553 prevent numpy deprecation warnings
+        pass
+    elif is_object_dtype(arr.dtype):
+        # pre-compute mask to avoid comparison to NA
+        # e.g. test_replace_na_in_obj_column
+        arr_mask = ~isna(arr)
+        mask[arr_mask] = arr[arr_mask] == value
     else:
-        for x in nonna:
-            if is_numeric_v_string_like(arr, x):
-                # GH#29553 prevent numpy deprecation warnings
-                pass
-            else:
-                if potential_na:
-                    new_mask = np.zeros(arr.shape, dtype=np.bool_)
-                    new_mask[arr_mask] = arr[arr_mask] == x
-                else:
-                    new_mask = arr == x
-
-                    if not isinstance(new_mask, np.ndarray):
-                        # usually BooleanArray
-                        new_mask = new_mask.to_numpy(dtype=bool, na_value=False)
-                mask |= new_mask
-
-    if na_mask.any():
-        mask |= isna(arr)
+        new_mask = arr == value
+
+        if not isinstance(new_mask, np.ndarray):
+            # usually BooleanArray
+            new_mask = new_mask.to_numpy(dtype=bool, na_value=False)
+        mask = new_mask
 
     return mask