Fixed isnan reference issue on Windows

Author: WillAyd

pandas/_libs/groupby.pyx

@@ -13,7 +13,6 @@ from numpy cimport (ndarray,
                     int8_t, int16_t, int32_t, int64_t, uint8_t, uint16_t,
                     uint32_t, uint64_t, float32_t, float64_t)
 
-from libc.math cimport isnan
 from libc.stdlib cimport malloc, free
 
 from util cimport numeric, get_nat
@@ -26,6 +25,9 @@ cdef int64_t iNaT = get_nat()
 cdef double NaN = <double> np.NaN
 cdef double nan = NaN
 
+cdef extern from "numpy/npy_math.h" nogil:
+    bint npy_isnan(double x)
+
 import missing
 
 

pandas/_libs/groupby_helper.pxi.in

@@ -535,8 +535,8 @@ def group_rank_{{name}}(ndarray[float64_t, ndim=2] out,
             {{else}}
             if (i == N - 1 or (
                     (masked_vals[_as[i]] != masked_vals[_as[i+1]]) and not
-                    (isnan(masked_vals[_as[i]]) and
-                     isnan(masked_vals[_as[i+1]])
+                    (npy_isnan(masked_vals[_as[i]]) and
+                     npy_isnan(masked_vals[_as[i+1]])
                     ))):
             {{endif}}
                 dups = sum_ranks = 0