/// <summary>Takes the top elements as if they were sorted.</summary>
/// <typeparam name="TSource">Specifies the type of the elements.</typeparam>
/// <typeparam name="TKey">Specifies the type of the keys used to compare elements.</typeparam>
/// <param name="source">The source elements.</param>
/// <param name="keySelector">A function used to extract a key from each element.</param>
/// <param name="count">The number of elements to take.</param>
/// <returns></returns>
public static IEnumerable <TSource> TakeTop <TSource, TKey>(this ParallelQuery <TSource> source,
Func <TSource, TKey> keySelector,
int count)
{
// We want to sort in descending order, so we need the opposite of the default comparer
var comparer = new DescendingDefaultComparer <TKey>();
// Aggregate, using a sorted list per thread to keep track of the best N elements,
// then merge those at the end.
return(source.Aggregate(
() => new SortedTopN <TKey, TSource>(count, comparer),
(accum, item) =>
{
accum.Add(keySelector(item), item);
return accum;
},
(accum1, accum2) =>
{
foreach (var item in accum2)
{
accum1.Add(item);
}
return accum1;
},
(accum) => accum.Values));
}
/// <summary>
/// 정렬이 되었다면, 지정된 갯수의 최상위 요소중 <paramref name="count"/> 수만큼 반환합니다.
/// </summary>
/// <typeparam name="TSource">요소의 수형</typeparam>
/// <typeparam name="TKey">요소 비교를 위한 Key의 수형</typeparam>
/// <param name="source">요소 집합</param>
/// <param name="keySelector">요소로부터 Key를 추출하는 Selector</param>
/// <param name="count">취할 요소의 수</param>
/// <returns></returns>
public static IEnumerable <TSource> TakeTop <TSource, TKey>(this ParallelQuery <TSource> source,
Func <TSource, TKey> keySelector,
int count = 1)
{
keySelector.ShouldNotBeNull("keySelector");
if (IsDebugEnabled)
{
log.Debug("최상의 요소 중 [{0}]만큼 열거합니다.", count);
}
var comparer = new DescendingDefaultComparer <TKey>();
return
(source.Aggregate(() => new SortedTopN <TKey, TSource>(count, comparer),
(accum, item) => {
accum.Add(keySelector(item), item);
return accum;
},
(accum1, accum2) => {
foreach (var item in accum2)
{
accum1.Add(item);
}
return accum1;
},
accum => accum.Values));
}
/// <summary>Takes the top elements as if they were sorted.</summary>
/// <typeparam name="TSource">Specifies the type of the elements.</typeparam>
/// <typeparam name="TKey">Specifies the type of the keys used to compare elements.</typeparam>
/// <param name="source">The source elements.</param>
/// <param name="keySelector">A function used to extract a key from each element.</param>
/// <param name="count">The number of elements to take.</param>
/// <returns></returns>
public static IEnumerable <TSource> TakeTop <TSource, TKey>(this ParallelQuery <TSource> source, Func <TSource, TKey> keySelector, int count)
{
DescendingDefaultComparer <TKey> comparer = new DescendingDefaultComparer <TKey>();
return(source.Aggregate <TSource, SortedTopN <TKey, TSource>, IEnumerable <TSource> >(() => new SortedTopN <TKey, TSource>(count, comparer), delegate(SortedTopN <TKey, TSource> accum, TSource item) {
accum.Add(keySelector(item), item);
return accum;
}, delegate(SortedTopN <TKey, TSource> accum1, SortedTopN <TKey, TSource> accum2) {
foreach (KeyValuePair <TKey, TSource> pair in accum2)
{
accum1.Add(pair);
}
return accum1;
}, accum => accum.Values));
}
