CLN: remove unused min_count argument in libgroupby.group_nth (#37747)

Author: arw2019

pandas/_libs/groupby.pyx

@@ -986,8 +986,8 @@ def group_last(rank_t[:, :] out,
 def group_nth(rank_t[:, :] out,
               int64_t[:] counts,
               ndarray[rank_t, ndim=2] values,
-              const int64_t[:] labels, int64_t rank=1,
-              Py_ssize_t min_count=-1):
+              const int64_t[:] labels, int64_t rank=1
+              ):
     """
     Only aggregates on axis=0
     """
@@ -998,8 +998,6 @@ def group_nth(rank_t[:, :] out,
         ndarray[int64_t, ndim=2] nobs
         bint runtime_error = False
 
-    assert min_count == -1, "'min_count' only used in add and prod"
-
     # TODO(cython 3.0):
     # Instead of `labels.shape[0]` use `len(labels)`
     if not len(values) == labels.shape[0]:

pandas/core/groupby/ops.py

@@ -603,8 +603,7 @@ def _aggregate(
     ):
         if agg_func is libgroupby.group_nth:
             # different signature from the others
-            # TODO: should we be using min_count instead of hard-coding it?
-            agg_func(result, counts, values, comp_ids, rank=1, min_count=-1)
+            agg_func(result, counts, values, comp_ids, rank=1)
         else:
             agg_func(result, counts, values, comp_ids, min_count)