Fixed bug with First tiebreak across multiple groups

Author: WillAyd

pandas/_libs/groupby.pyx

@@ -18,7 +18,7 @@ from libc.stdlib cimport malloc, free
 
 from util cimport numeric, get_nat
 from algos cimport (swap, TIEBREAK_AVERAGE, TIEBREAK_MIN, TIEBREAK_MAX,
-                    TIEBREAK_FIRST, TIEBREAK_FIRST_DESCENDING, TIEBREAK_DENSE)
+                    TIEBREAK_FIRST, TIEBREAK_DENSE)
 from algos import take_2d_axis1_float64_float64, groupsort_indexer, tiebreakers
 
 cdef int64_t iNaT = get_nat()
@@ -189,9 +189,9 @@ def group_rank_object(ndarray[float64_t, ndim=2] out,
             elif tiebreak == TIEBREAK_FIRST:
                 for j in range(i - dups + 1, i + 1):
                     if ascending:
-                        out[_as[j], 0] = j + 1
+                        out[_as[j], 0] = j + 1 - grp_start
                     else:
-                        out[_as[j], 0] = 2 * i - j - dups + 2
+                        out[_as[j], 0] = 2 * i - j - dups + 2 - grp_start
             elif tiebreak == TIEBREAK_DENSE:
                 for j in range(i - dups + 1, i + 1):
                     out[_as[j], 0] = vals_seen

pandas/_libs/groupby_helper.pxi.in

@@ -520,9 +520,9 @@ def group_rank_{{name}}(ndarray[float64_t, ndim=2] out,
                 elif tiebreak == TIEBREAK_FIRST:
                     for j in range(i - dups + 1, i + 1):
                         if ascending:
-                            out[_as[j], 0] = j + 1
+                            out[_as[j], 0] = j + 1 - grp_start
                         else:
-                            out[_as[j], 0] = 2 * i - j - dups + 2
+                            out[_as[j], 0] = 2 * i - j - dups + 2 - grp_start
                 elif tiebreak == TIEBREAK_DENSE:
                     for j in range(i - dups + 1, i + 1):
                         out[_as[j], 0] = vals_seen