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Simplify Enumerable.AggregateBy #109110

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84 changes: 29 additions & 55 deletions src/libraries/System.Linq/src/System/Linq/AggregateBy.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -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>
Expand Down Expand Up @@ -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;
}
}
}
15 changes: 1 addition & 14 deletions src/libraries/System.Linq/src/System/Linq/CountBy.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down