diff --git a/src/libraries/System.Linq/src/System/Linq/AggregateBy.cs b/src/libraries/System.Linq/src/System/Linq/AggregateBy.cs
index 054b1272db115a..53d81ae4faf536 100644
--- a/src/libraries/System.Linq/src/System/Linq/AggregateBy.cs
+++ b/src/libraries/System.Linq/src/System/Linq/AggregateBy.cs
@@ -49,7 +49,26 @@ public static IEnumerable<KeyValuePair<TKey, TAccumulate>> AggregateBy<TSource,
                 return [];
             }
 
-            return AggregateByIterator(source, keySelector, seed, func, keyComparer);
+            using IEnumerator<TSource> enumerator = source.GetEnumerator();
+
+            if (!enumerator.MoveNext())
+            {
+                return [];
+            }
+
+            Dictionary<TKey, TAccumulate> dict = new(keyComparer);
+
+            do
+            {
+                TSource value = enumerator.Current;
+                TKey key = keySelector(value);
+
+                ref TAccumulate? acc = ref CollectionsMarshal.GetValueRefOrAddDefault(dict, key, out bool exists);
+                acc = func(exists ? acc! : seed, value);
+            }
+            while (enumerator.MoveNext());
+
+            return dict;
         }
 
         /// <summary>
@@ -97,71 +116,26 @@ public static IEnumerable<KeyValuePair<TKey, TAccumulate>> AggregateBy<TSource,
                 return [];
             }
 
-            return AggregateByIterator(source, keySelector, seedSelector, func, keyComparer);
-        }
-
-        private static IEnumerable<KeyValuePair<TKey, TAccumulate>> AggregateByIterator<TSource, TKey, TAccumulate>(IEnumerable<TSource> source, Func<TSource, TKey> keySelector, TAccumulate seed, Func<TAccumulate, TSource, TAccumulate> func, IEqualityComparer<TKey>? keyComparer) where TKey : notnull
-        {
             using IEnumerator<TSource> enumerator = source.GetEnumerator();
 
             if (!enumerator.MoveNext())
             {
-                yield break;
-            }
-
-            foreach (KeyValuePair<TKey, TAccumulate> countBy in PopulateDictionary(enumerator, keySelector, seed, func, keyComparer))
-            {
-                yield return countBy;
-            }
-
-            static Dictionary<TKey, TAccumulate> PopulateDictionary(IEnumerator<TSource> enumerator, Func<TSource, TKey> keySelector, TAccumulate seed, Func<TAccumulate, TSource, TAccumulate> func, IEqualityComparer<TKey>? keyComparer)
-            {
-                Dictionary<TKey, TAccumulate> dict = new(keyComparer);
-
-                do
-                {
-                    TSource value = enumerator.Current;
-                    TKey key = keySelector(value);
-
-                    ref TAccumulate? acc = ref CollectionsMarshal.GetValueRefOrAddDefault(dict, key, out bool exists);
-                    acc = func(exists ? acc! : seed, value);
-                }
-                while (enumerator.MoveNext());
-
-                return dict;
+                return [];
             }
-        }
 
-        private static IEnumerable<KeyValuePair<TKey, TAccumulate>> AggregateByIterator<TSource, TKey, TAccumulate>(IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TKey, TAccumulate> seedSelector, Func<TAccumulate, TSource, TAccumulate> func, IEqualityComparer<TKey>? keyComparer) where TKey : notnull
-        {
-            using IEnumerator<TSource> enumerator = source.GetEnumerator();
+            Dictionary<TKey, TAccumulate> dict = new(keyComparer);
 
-            if (!enumerator.MoveNext())
+            do
             {
-                yield break;
-            }
+                TSource value = enumerator.Current;
+                TKey key = keySelector(value);
 
-            foreach (KeyValuePair<TKey, TAccumulate> countBy in PopulateDictionary(enumerator, keySelector, seedSelector, func, keyComparer))
-            {
-                yield return countBy;
+                ref TAccumulate? acc = ref CollectionsMarshal.GetValueRefOrAddDefault(dict, key, out bool exists);
+                acc = func(exists ? acc! : seedSelector(key), value);
             }
+            while (enumerator.MoveNext());
 
-            static Dictionary<TKey, TAccumulate> PopulateDictionary(IEnumerator<TSource> enumerator, Func<TSource, TKey> keySelector, Func<TKey, TAccumulate> seedSelector, Func<TAccumulate, TSource, TAccumulate> func, IEqualityComparer<TKey>? keyComparer)
-            {
-                Dictionary<TKey, TAccumulate> dict = new(keyComparer);
-
-                do
-                {
-                    TSource value = enumerator.Current;
-                    TKey key = keySelector(value);
-
-                    ref TAccumulate? acc = ref CollectionsMarshal.GetValueRefOrAddDefault(dict, key, out bool exists);
-                    acc = func(exists ? acc! : seedSelector(key), value);
-                }
-                while (enumerator.MoveNext());
-
-                return dict;
-            }
+            return dict;
         }
     }
 }
diff --git a/src/libraries/System.Linq/src/System/Linq/CountBy.cs b/src/libraries/System.Linq/src/System/Linq/CountBy.cs
index 43b450f309cda6..412d67caf3f5fe 100644
--- a/src/libraries/System.Linq/src/System/Linq/CountBy.cs
+++ b/src/libraries/System.Linq/src/System/Linq/CountBy.cs
@@ -33,26 +33,13 @@ public static IEnumerable<KeyValuePair<TKey, int>> CountBy<TSource, TKey>(this I
                 return [];
             }
 
-            return CountByIterator(source, keySelector, keyComparer);
-        }
-
-        private static IEnumerable<KeyValuePair<TKey, int>> CountByIterator<TSource, TKey>(IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey>? keyComparer) where TKey : notnull
-        {
             using IEnumerator<TSource> enumerator = source.GetEnumerator();
 
             if (!enumerator.MoveNext())
             {
-                yield break;
-            }
-
-            foreach (KeyValuePair<TKey, int> countBy in BuildCountDictionary(enumerator, keySelector, keyComparer))
-            {
-                yield return countBy;
+                return [];
             }
-        }
 
-        private static Dictionary<TKey, int> BuildCountDictionary<TSource, TKey>(IEnumerator<TSource> enumerator, Func<TSource, TKey> keySelector, IEqualityComparer<TKey>? keyComparer) where TKey : notnull
-        {
             Dictionary<TKey, int> countsBy = new(keyComparer);
 
             do