/// <summary>Returns the minimum value in a generic sequence according to a specified key selector function.</summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source" />.</typeparam>
/// <typeparam name="TKey">The type of key to compare elements by.</typeparam>
/// <param name="source">A sequence of values to determine the minimum value of.</param>
/// <param name="keySelector">A function to extract the key for each element.</param>
/// <param name="comparer">The <see cref="IComparer{TKey}" /> to compare keys.</param>
/// <returns>The value with the minimum key in the sequence.</returns>
/// <exception cref="ArgumentNullException"><paramref name="source" /> is <see langword="null" />.</exception>
/// <exception cref="ArgumentException">No key extracted from <paramref name="source" /> implements the <see cref="IComparable" /> or <see cref="IComparable{TKey}" /> interface.</exception>
/// <remarks>
/// <para>If <typeparamref name="TKey" /> is a reference type and the source sequence is empty or contains only values that are <see langword="null" />, this method returns <see langword="null" />.</para>
/// </remarks>
public static TSource?MinBy <TSource, TKey>(this IEnumerable <TSource> source, Func <TSource, TKey> keySelector, IComparer <TKey>?comparer)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
if (keySelector == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.keySelector);
}
comparer ??= Comparer <TKey> .Default;
using IEnumerator <TSource> e = source.GetEnumerator();
if (!e.MoveNext())
{
if (default(TSource) is null)
{
return(default);
public static long?Min(this IEnumerable <long?> source)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
long?value = null;
using (IEnumerator <long?> e = source.GetEnumerator())
{
do
{
if (!e.MoveNext())
{
return(value);
}
value = e.Current;
}while (!value.HasValue);
long valueVal = value.GetValueOrDefault();
while (e.MoveNext())
{
long?cur = e.Current;
long x = cur.GetValueOrDefault();
// Do not replace & with &&. The branch prediction cost outweighs the extra operation
// unless nulls either never happen or always happen.
if (cur.HasValue & x < valueVal)
{
valueVal = x;
value = cur;
}
}
}
return(value);
}
public static long LongCount <TSource>(this IEnumerable <TSource> source)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
long count = 0;
using (IEnumerator <TSource> e = source.GetEnumerator())
{
checked
{
while (e.MoveNext())
{
count++;
}
}
}
return(count);
}
public static Dictionary <TKey, TElement> ToDictionary <TSource, TKey, TElement>(IEnumerable <TSource> source, Func <TSource, TKey> keySelector, Func <TSource, TElement> elementSelector, IEqualityComparer <TKey> comparer)
{
if (source == null)
{
throw ThrowHelper.ArgumentNull("source");
}
if (keySelector == null)
{
throw ThrowHelper.ArgumentNull("keySelector");
}
if (elementSelector == null)
{
throw ThrowHelper.ArgumentNull("elementSelector");
}
Dictionary <TKey, TElement> tKeys = new Dictionary <TKey, TElement>(comparer);
foreach (TSource tSource in source)
{
tKeys.Add(keySelector(tSource), elementSelector(tSource));
}
return(tKeys);
}
public static TSource Single <TSource>(this IEnumerable <TSource> source)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
if (source is IList <TSource> list)
{
switch (list.Count)
{
case 0:
ThrowHelper.ThrowNoElementsException();
return(default);
case 1:
return(list[0]);
}
}
else
{
using (IEnumerator <TSource> e = source.GetEnumerator())
{
if (!e.MoveNext())
{
ThrowHelper.ThrowNoElementsException();
}
TSource result = e.Current;
if (!e.MoveNext())
{
return(result);
}
}
}
ThrowHelper.ThrowMoreThanOneElementException();
return(default);
public static double Min(this IEnumerable <double> source)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
double value;
using (IEnumerator <double> e = source.GetEnumerator())
{
if (!e.MoveNext())
{
ThrowHelper.ThrowNoElementsException();
}
value = e.Current;
if (double.IsNaN(value))
{
return(value);
}
while (e.MoveNext())
{
double x = e.Current;
if (x < value)
{
value = x;
}
else if (double.IsNaN(x))
{
return(x);
}
}
}
return(value);
}
public static int Count <TSource>(this IEnumerable <TSource> source)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
if (source is ICollection <TSource> collectionoft)
{
return(collectionoft.Count);
}
if (source is IIListProvider <TSource> listProv)
{
return(listProv.GetCount(onlyIfCheap: false));
}
if (source is ICollection collection)
{
return(collection.Count);
}
int count = 0;
using (IEnumerator <TSource> e = source.GetEnumerator())
{
checked
{
while (e.MoveNext())
{
count++;
}
}
}
return(count);
}
public static decimal?Min(this IEnumerable <decimal?> source)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
decimal?value = null;
using (IEnumerator <decimal?> e = source.GetEnumerator())
{
do
{
if (!e.MoveNext())
{
return(value);
}
value = e.Current;
}while (!value.HasValue);
decimal valueVal = value.GetValueOrDefault();
while (e.MoveNext())
{
decimal?cur = e.Current;
decimal x = cur.GetValueOrDefault();
if (cur.HasValue && x < valueVal)
{
valueVal = x;
value = cur;
}
}
}
return(value);
}
/// <summary>Returns the minimum value in a generic sequence.</summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source" />.</typeparam>
/// <param name="source">A sequence of values to determine the minimum value of.</param>
/// <param name="comparer">The <see cref="IComparer{T}" /> to compare values.</param>
/// <returns>The minimum value in the sequence.</returns>
/// <exception cref="ArgumentNullException"><paramref name="source" /> is <see langword="null" />.</exception>
/// <exception cref="ArgumentException">No object in <paramref name="source" /> implements the <see cref="System.IComparable" /> or <see cref="System.IComparable{T}" /> interface.</exception>
/// <remarks>
/// <para>If type <typeparamref name="TSource" /> implements <see cref="System.IComparable{T}" />, the <see cref="Max{T}(IEnumerable{T})" /> method uses that implementation to compare values. Otherwise, if type <typeparamref name="TSource" /> implements <see cref="System.IComparable" />, that implementation is used to compare values.</para>
/// <para>If <typeparamref name="TSource" /> is a reference type and the source sequence is empty or contains only values that are <see langword="null" />, this method returns <see langword="null" />.</para>
/// <para>In Visual Basic query expression syntax, an `Aggregate Into Max()` clause translates to an invocation of <see cref="O:Enumerable.Max" />.</para>
/// </remarks>
public static TSource?Min <TSource>(this IEnumerable <TSource> source, IComparer <TSource>?comparer)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
comparer ??= Comparer <TSource> .Default;
TSource?value = default;
using (IEnumerator <TSource> e = source.GetEnumerator())
{
if (value == null)
{
do
{
if (!e.MoveNext())
{
return(value);
}
value = e.Current;
}while (value == null);
while (e.MoveNext())
{
TSource next = e.Current;
if (next != null && comparer.Compare(next, value) < 0)
{
value = next;
}
}
}
else
{
if (!e.MoveNext())
{
ThrowHelper.ThrowNoElementsException();
}
value = e.Current;
if (comparer == Comparer <TSource> .Default)
{
while (e.MoveNext())
{
TSource next = e.Current;
if (Comparer <TSource> .Default.Compare(next, value) < 0)
{
value = next;
}
}
}
else
{
while (e.MoveNext())
{
TSource next = e.Current;
if (comparer.Compare(next, value) < 0)
{
value = next;
}
}
}
}
}
return(value);
}
void IList <TElement> .RemoveAt(int index) => ThrowHelper.ThrowNotSupportedException();
void IList <TElement> .Insert(int index, TElement item) => ThrowHelper.ThrowNotSupportedException();
bool ICollection <TElement> .Remove(TElement item)
{
ThrowHelper.ThrowNotSupportedException();
return(false);
}
void ICollection <TElement> .Clear() => ThrowHelper.ThrowNotSupportedException();
void ICollection <TElement> .Add(TElement item) => ThrowHelper.ThrowNotSupportedException();
private static IEnumerable <TSource> ElementsInIterator <TSource>(IEnumerable <TSource> source, Range range)
{
Index start = range.Start;
Index end = range.End;
if (source is IList <TSource> list)
{
int count = list.Count;
if (count == 0 && range.Equals(System.Range.All))
{
yield break;
}
int firstIndex = start.IsFromEnd ? count - start.Value : start.Value;
int lastIndex = (end.IsFromEnd ? count - end.Value : end.Value) - 1;
if (lastIndex < firstIndex - 1)
{
ThrowHelper.ThrowOverflowException(); // Following the behavior of array with range.
}
if (firstIndex < 0 || lastIndex < 0)
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.range); // Following the behavior of array with range.
}
if (firstIndex >= count || lastIndex >= count)
{
ThrowHelper.ThrowArgumentException(ExceptionArgument.range); // Following the behavior of array with range.
}
for (int currentIndex = firstIndex; currentIndex <= lastIndex; currentIndex++)
{
yield return(list[currentIndex]);
}
yield break;
}
using (IEnumerator <TSource> e = source.GetEnumerator())
{
int currentIndex = -1;
if (start.IsFromEnd)
{
if (!e.MoveNext())
{
const int count = 0;
int firstIndex = count - start.Value;
int lastIndex = (end.IsFromEnd ? count - end.Value : end.Value) - 1;
if (lastIndex < firstIndex - 1)
{
ThrowHelper.ThrowOverflowException(); // Following the behavior of array with range.
}
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.range); // Following the behavior of array with range.
}
else
{
Queue <TSource> queue = new Queue <TSource>();
queue.Enqueue(e.Current);
currentIndex++;
int takeLastCount = start.Value;
while (e.MoveNext())
{
if (queue.Count == takeLastCount)
{
queue.Dequeue();
}
queue.Enqueue(e.Current);
currentIndex++;
}
if (queue.Count < takeLastCount)
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.range); // Following the behavior of array with range.
}
int firstIndex = currentIndex + 1 - takeLastCount;
int lastIndex = end.IsFromEnd ? currentIndex - end.Value : end.Value - 1;
if (lastIndex < firstIndex - 1)
{
ThrowHelper.ThrowOverflowException(); // Following the behavior of array with range.
}
for (int index = firstIndex; index <= lastIndex; index++)
{
yield return(queue.Dequeue());
}
}
}
else
{
int firstIndex = start.Value;
if (!e.MoveNext())
{
if (range.Equals(System.Range.All))
{
yield break;
}
const int count = 0;
int lastIndex = (end.IsFromEnd ? count - end.Value : end.Value) - 1;
if (lastIndex < firstIndex - 1)
{
ThrowHelper.ThrowOverflowException(); // Following the behavior of array with range.
}
ThrowHelper.ThrowArgumentException(ExceptionArgument.range); // Following the behavior of array with range.
}
currentIndex++;
while (currentIndex < firstIndex && e.MoveNext())
{
currentIndex++;
}
if (currentIndex != firstIndex)
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.range); // Following the behavior of array with range.
}
if (end.IsFromEnd)
{
int skipLastCount = end.Value;
if (skipLastCount > 0)
{
Queue <TSource> queue = new Queue <TSource>();
do
{
if (queue.Count == skipLastCount)
{
yield return(queue.Dequeue());
}
queue.Enqueue(e.Current);
currentIndex++;
}while (e.MoveNext());
}
else
{
do
{
yield return(e.Current);
currentIndex++;
}while (e.MoveNext());
}
if (firstIndex + skipLastCount > currentIndex)
{
ThrowHelper.ThrowOverflowException(); // Following the behavior of array with range.
}
}
else
{
int lastIndex = end.Value - 1;
if (lastIndex < firstIndex - 1)
{
ThrowHelper.ThrowOverflowException(); // Following the behavior of array with range.
}
if (lastIndex == firstIndex - 1)
{
yield break;
}
yield return(e.Current);
while (currentIndex < lastIndex && e.MoveNext())
{
currentIndex++;
yield return(e.Current);
}
if (currentIndex != lastIndex)
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.range); // Following the behavior of array with range.
}
}
}
}
}
