place start and end mark

src/components/ChartView.vue

@@ -39,9 +39,12 @@ export default {
         for (let i = 0; i < this.data.length; i++) {
           const data = this.data[i];
           const val = resolve_data (data, y.field);
+          const next = this.data.length - 1 === i
+            ? val
+            : resolve_data (this.data[i + 1], y.field);
           if (
             !this.remove_duplicates
-            || last !== val
+            || last !== val || next !== val
             || this.data.length - 1 === i
           )
             res.data.push (val);