Unnecessary outer loop in CountBy #106110
Description
The implementation of the new CountBy adds an unnecessary outer loop through the dictionary elements.
runtime/src/libraries/System.Linq/src/System/Linq/CountBy.cs
Lines 39 to 42 in 019d758
I think we can return created Dictionary enumerator:
public static IEnumerable<KeyValuePair<TKey, int>> CountBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey>? keyComparer = null) where TKey : notnull
{
// Same code
return new CountByEnumerable<TSource, TKey>(source, keySelector, keyComparer);
}
private sealed class CountByEnumerable<TSource, TKey>(IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey>? keyComparer) : IEnumerable<KeyValuePair<TKey, int>> where TKey : notnull
{
public IEnumerator<KeyValuePair<TKey, int>> GetEnumerator()
{
using IEnumerator<TSource> enumerator = source.GetEnumerator();
if (!enumerator.MoveNext())
{
return Empty<KeyValuePair<TKey, int>>().GetEnumerator();
}
return BuildCountDictionary(enumerator, keySelector, keyComparer).GetEnumerator();
}
}