From 982ab6dad08e55c3ed36ddc5d934ad47033f0544 Mon Sep 17 00:00:00 2001
From: Daniel Saxton <dsaxton@pm.me>
Date: Sat, 11 Apr 2020 20:50:06 -0500
Subject: [PATCH] Implement pd.NA checking function

---
 pandas/_libs/missing.pyx            | 27 +++++++++++++++++++++++++++
 pandas/tests/dtypes/test_missing.py |  6 ++++++
 2 files changed, 33 insertions(+)

diff --git a/pandas/_libs/missing.pyx b/pandas/_libs/missing.pyx
index dacf454824190..d18dad343c7c0 100644
--- a/pandas/_libs/missing.pyx
+++ b/pandas/_libs/missing.pyx
@@ -129,6 +129,33 @@ cpdef ndarray[uint8_t] isnaobj(ndarray arr):
     return result.view(np.bool_)
 
 
+cpdef ndarray[uint8_t] ispdna(ndarray arr):
+    """
+    Return boolean mask denoting which elements of a 1-D array are pd.NA.
+
+    Parameters
+    ----------
+    arr : ndarray
+
+    Returns
+    -------
+    result : ndarray (dtype=np.bool_)
+    """
+
+    cdef:
+        Py_ssize_t i, n
+        ndarray[uint8_t] result
+
+    assert arr.ndim == 1, "'arr' must be 1-D."
+
+    n = len(arr)
+    result = np.empty(n, dtype=np.uint8)
+    for i in range(n):
+        result[i] = arr[i] is C_NA
+
+    return result.view(np.bool_)
+
+
 @cython.wraparound(False)
 @cython.boundscheck(False)
 def isnaobj_old(arr: ndarray) -> ndarray:
diff --git a/pandas/tests/dtypes/test_missing.py b/pandas/tests/dtypes/test_missing.py
index cad46d0a23967..99c86756e9552 100644
--- a/pandas/tests/dtypes/test_missing.py
+++ b/pandas/tests/dtypes/test_missing.py
@@ -599,3 +599,9 @@ def test_is_null_datetimelike(self):
 
         for value in never_na_vals:
             assert not is_null_datetimelike(value)
+
+    def test_ispdna(self):
+        values = np.array([0, np.nan, None, pd.NaT, pd.NA])
+        result = libmissing.ispdna(values)
+        expected = np.array([False, False, False, False, True], dtype=np.bool_)
+        tm.assert_numpy_array_equal(result, expected)