From 4ff71b2565b982efdcce92ccbdde81c6f71b73a4 Mon Sep 17 00:00:00 2001
From: Marco Gorelli <33491632+MarcoGorelli@users.noreply.github.com>
Date: Tue, 19 Mar 2024 21:44:39 +0000
Subject: [PATCH] modin can use fastpath too

---
 narwhals/pandas_like/utils.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/narwhals/pandas_like/utils.py b/narwhals/pandas_like/utils.py
index bdfbb5955..9486e94fb 100644
--- a/narwhals/pandas_like/utils.py
+++ b/narwhals/pandas_like/utils.py
@@ -234,7 +234,11 @@ def evaluate_simple_aggregation(expr: PandasExpr, grouped: Any, keys: list[str])
     if expr._depth == 0:
         # e.g. agg(pl.len())
         df = getattr(grouped, expr._function_name.replace("len", "size"))()
-        df = df.drop(columns=keys) if len(df.shape) > 1 else df.to_frame("size")
+        df = (
+            df.drop(columns=keys)
+            if len(df.shape) > 1
+            else df.reset_index(drop=True).to_frame("size")
+        )
         return df.rename(columns={"size": expr._output_names[0]})  # type: ignore[index]
     if expr._root_names is None or expr._output_names is None:
         msg = "Expected expr to have root_names and output_names set, but they are None. Please report a bug."