diff --git a/optuna_dashboard/ts/components/GraphRank.tsx b/optuna_dashboard/ts/components/GraphRank.tsx
index 17731101..6030a722 100644
--- a/optuna_dashboard/ts/components/GraphRank.tsx
+++ b/optuna_dashboard/ts/components/GraphRank.tsx
@@ -275,9 +275,7 @@ const getOrderWithSameOrderAveraging = (values: number[]): number[] => {
   values.forEach((value) => {
     const first_index = sorted_values.indexOf(value)
     const last_index = sorted_values.lastIndexOf(value)
-    const sum_of_the_value = sorted_values
-      .slice(first_index, last_index + 1)
-      .reduce((a, b) => a + b, 0)
+    const sum_of_the_value = (first_index + last_index) * (last_index - first_index + 1) / 2
     const rank = sum_of_the_value / (last_index - first_index + 1)
     ranks.push(rank)
   })