public IOrderedEnumerable <TElement> CreateOrderedEnumerable <TNewKey>(Func <TElement, TNewKey> keySelector, IComparer <TNewKey> comparer, bool descending)
{
comparer = comparer ?? Comparer <TNewKey> .Default;
if (descending)
{
comparer = comparer.Reverse();
}
var compoundComparer = new CustomComparer <(TKey, TNewKey)>(Compare);
return(new OrderedEnumerable <TElement, (TKey, TNewKey)>(_source, CompoundKeySelector, compoundComparer));
(TKey, TNewKey) CompoundKeySelector(TElement item)
{
return(_keySelector(item), keySelector(item));
}
int Compare((TKey, TNewKey) x, (TKey, TNewKey) y)
{
var check = _comparer.Compare(x.Item1, y.Item1);
if (check == 0)
{
return(comparer.Compare(x.Item2, y.Item2));
}
return(check);
}
}
/// <summary>
/// Sorts the elements of a sequence in descending order according to a key.
/// Unlike standard Linq NOT a stable sort.
/// </summary>
/// <param name="source">A sequence of values to order.</param>
/// <param name="keySelector">A function to extract a key from an element.</param>
/// <param name="comparer">A Comparer to compare keys.</param>
/// <returns>A sequence whose elements are ordered according to a key</returns>
public static TSource[] OrderByDescendingF <TSource, TKey>(this TSource[] source, Func <TSource, TKey> keySelector, IComparer <TKey> comparer = null)
{
if (source == null)
{
throw Error.ArgumentNull(nameof(source));
}
if (keySelector == null)
{
throw Error.ArgumentNull("keySelector");
}
if (comparer == null)
{
comparer = Comparer <TKey> .Default;
}
TKey[] keys = new TKey[source.Length];
for (int i = 0; i < keys.Length; i++)
{
keys[i] = keySelector(source[i]);
}
TSource[] result = (TSource[])source.Clone();
Array.Sort(keys, result, comparer.Reverse());
return(result);
}
public IOrderedEnumerable <TElement> CreateOrderedEnumerable <TNewKey>(Func <TElement, TNewKey> keySelector, IComparer <TNewKey> comparer, bool descending)
{
if (keySelector == null)
{
throw new ArgumentNullException(nameof(keySelector));
}
comparer = comparer ?? Comparer <TNewKey> .Default;
if (descending)
{
comparer = comparer.Reverse();
}
var compoundComparer = new CustomComparer <KeyValuePair <TKey, TNewKey> >(Compare);
return(new OrderedEnumerable <TElement, KeyValuePair <TKey, TNewKey> >(_source, CompoundKeySelector, compoundComparer));
KeyValuePair <TKey, TNewKey> CompoundKeySelector(TElement item)
{
return(new KeyValuePair <TKey, TNewKey>(_keySelector(item), keySelector(item)));
}
int Compare(KeyValuePair <TKey, TNewKey> x, KeyValuePair <TKey, TNewKey> y)
{
var check = _comparer.Compare(x.Key, y.Key);
return(check == 0 ? comparer.Compare(x.Value, y.Value) : check);
}
}
public IOrderedEnumerable <TElement> CreateOrderedEnumerable <TNewKey>(Func <TElement, TNewKey> keySelector, IComparer <TNewKey> comparer, bool descending)
{
comparer = comparer ?? Comparer <TNewKey> .Default;
if (descending)
{
comparer = comparer.Reverse();
}
return(new OrderedEnumerable <TElement, TNewKey>(_source, keySelector, comparer));
}
public OrderedEnumerable(IEnumerable <TElement> source, Func <TElement, TKey> keySelector, IComparer <TKey> comparer, bool descending)
{
_comparer = comparer ?? Comparer <TKey> .Default;
if (descending)
{
_comparer = _comparer.Reverse();
}
_source = source ?? throw new ArgumentNullException(nameof(source));
_keySelector = keySelector ?? throw new ArgumentNullException(nameof(keySelector));
}
public void SubstitutesCompareDefaultForNull()
{
IComparer <int> source = null;
var comparer = source.Reverse();
Assert.Equal(ComparerBuilder.For <int>().Default().Reverse().ToString(), comparer.ToString());
var list = Enumerable.Range(0, 5).ToList();
list.Sort(comparer);
Assert.Equal(new[] { 4, 3, 2, 1, 0 }, list);
}
public int ShouldExtendComparerByReverseMethod(IComparer <object> comparer)
{
// given
var obj1 = new object();
var obj2 = new object();
// when
var reverse = comparer.Reverse();
// then
return(reverse.Compare(obj1, obj2));
}
public void SubstitutesCompareDefaultForNull()
{
IComparer <int> source = null;
var comparer = source.Reverse();
Assert.AreSame(Compare <int> .Default(), (comparer as ReverseComparer <int>).Source);
var list = Enumerable.Range(0, 5).ToList();
list.Sort(comparer);
CollectionAssert.AreEqual(new[] { 4, 3, 2, 1, 0 }, list);
}
/// <summary> /// Returns a comparer that uses another comparer if the source comparer determines the objects are equal. /// </summary> /// <typeparam name="T">The type of objects being compared.</typeparam> /// <param name="source">The source comparer. If this is <c>null</c>, the default comparer is used.</param> /// <param name="thenBy">The comparer that is used if <paramref name="source"/> determines the objects are equal. If this is <c>null</c>, the default comparer is used.</param> /// <param name="descending">A value indicating whether the sorting is done in descending order. If <c>false</c> (the default), then the sort is in ascending order.</param> /// <returns>A comparer that uses another comparer if the source comparer determines the objects are equal.</returns> public static IFullComparer <T> ThenBy <T>(this IComparer <T> source, IComparer <T> thenBy, bool descending = false) => new CompoundComparer <T>(source, descending ? thenBy.Reverse() : thenBy);
/// <summary>
/// The implementaiton of SEARCH-LAYER(q, ep, ef, lc) algorithm.
/// Article: Section 4. Algorithm 2.
/// </summary>
/// <param name="entryPointId">The identifier of the entry point for the search.</param>
/// <param name="targetCosts">The traveling costs for the search target.</param>
/// <param name="resultList">The list of identifiers of the nearest neighbours at the level.</param>
/// <param name="layer">The layer to perform search at.</param>
/// <param name="k">The number of the nearest neighbours to get from the layer.</param>
internal void RunKnnAtLayer(int entryPointId, TravelingCosts <int, TDistance> targetCosts, IList <int> resultList, int layer, int k)
{
/*
* v ← ep // set of visited elements
* C ← ep // set of candidates
* W ← ep // dynamic list of found nearest neighbors
* while │C│ > 0
* c ← extract nearest element from C to q
* f ← get furthest element from W to q
* if distance(c, q) > distance(f, q)
* break // all elements in W are evaluated
* for each e ∈ neighbourhood(c) at layer lc // update C and W
* if e ∉ v
* v ← v ⋃ e
* f ← get furthest element from W to q
* if distance(e, q) < distance(f, q) or │W│ < ef
* C ← C ⋃ e
* W ← W ⋃ e
* if │W│ > ef
* remove furthest element from W to q
* return W
*/
// prepare tools
IComparer <int> fartherIsOnTop = targetCosts;
IComparer <int> closerIsOnTop = fartherIsOnTop.Reverse();
// prepare collections
// TODO: Optimize by providing buffers
var resultHeap = new BinaryHeap <int>(resultList, fartherIsOnTop);
var expansionHeap = new BinaryHeap <int>(this.expansionBuffer, closerIsOnTop);
resultHeap.Push(entryPointId);
expansionHeap.Push(entryPointId);
this.visitedSet.Add(entryPointId);
// run bfs
while (expansionHeap.Buffer.Count > 0)
{
// get next candidate to check and expand
var toExpandId = expansionHeap.Pop();
var farthestResultId = resultHeap.Buffer[0];
if (DistanceUtils.Gt(targetCosts.From(toExpandId), targetCosts.From(farthestResultId)))
{
// the closest candidate is farther than farthest result
break;
}
// expand candidate
var neighboursIds = this.core.Nodes[toExpandId][layer];
for (int i = 0; i < neighboursIds.Count; ++i)
{
int neighbourId = neighboursIds[i];
if (!this.visitedSet.Contains(neighbourId))
{
// enque perspective neighbours to expansion list
farthestResultId = resultHeap.Buffer[0];
if (resultHeap.Buffer.Count < k ||
DistanceUtils.Lt(targetCosts.From(neighbourId), targetCosts.From(farthestResultId)))
{
expansionHeap.Push(neighbourId);
resultHeap.Push(neighbourId);
if (resultHeap.Buffer.Count > k)
{
resultHeap.Pop();
}
}
// update visited list
this.visitedSet.Add(neighbourId);
}
}
}
this.expansionBuffer.Clear();
this.visitedSet.Clear();
}
/// <summary>
/// Returns a comparer that uses another comparer if the source comparer determines the objects are equal.
/// </summary>
/// <typeparam name="T">The type of objects being compared.</typeparam>
/// <param name="source">The source comparer. If this is <c>null</c>, the default comparer is used.</param>
/// <param name="thenBy">The comparer that is used if <paramref name="source"/> determines the objects are equal. If this is <c>null</c>, the default comparer is used.</param>
/// <param name="descending">A value indicating whether the sorting is done in descending order. If <c>false</c> (the default), then the sort is in ascending order.</param>
/// <returns>A comparer that uses another comparer if the source comparer determines the objects are equal.</returns>
public static IFullComparer <T> ThenBy <T>(this IComparer <T> source, IComparer <T> thenBy, bool descending = false)
{
Contract.Ensures(Contract.Result <IFullComparer <T> >() != null);
return(new CompoundComparer <T>(source, descending ? thenBy.Reverse() : thenBy));
}
/// <summary>
/// The implementaiton of SEARCH-LAYER(q, ep, ef, lc) algorithm.
/// Article: Section 4. Algorithm 2.
/// </summary>
/// <param name="entryPoint">The entry point for the search.</param>
/// <param name="destination">The search target.</param>
/// <param name="k">The number of the nearest neighbours to get from the layer.</param>
/// <param name="level">Level of the layer.</param>
/// <returns>The list of the nearest neighbours at the level.</returns>
private static IList <Node> KNearestAtLevel(Node entryPoint, Node destination, int k, int level)
{
/*
* v ← ep // set of visited elements
* C ← ep // set of candidates
* W ← ep // dynamic list of found nearest neighbors
* while │C│ > 0
* c ← extract nearest element from C to q
* f ← get furthest element from W to q
* if distance(c, q) > distance(f, q)
* break // all elements in W are evaluated
* for each e ∈ neighbourhood(c) at layer lc // update C and W
* if e ∉ v
* v ← v ⋃ e
* f ← get furthest element from W to q
* if distance(e, q) < distance(f, q) or │W│ < ef
* C ← C ⋃ e
* W ← W ⋃ e
* if │W│ > ef
* remove furthest element from W to q
* return W
*/
// prepare tools
IComparer <Node> closerIsLess = destination.TravelingCosts;
IComparer <Node> fartherIsLess = closerIsLess.Reverse();
// prepare heaps
var resultHeap = new BinaryHeap <Node>(new List <Node>(k + 1)
{
entryPoint
}, closerIsLess);
var expansionHeap = new BinaryHeap <Node>(new List <Node>()
{
entryPoint
}, fartherIsLess);
// run bfs
var visited = new HashSet <int>()
{
entryPoint.Id
};
while (expansionHeap.Buffer.Any())
{
// get next candidate to check and expand
var toExpand = expansionHeap.Pop();
var farthestResult = resultHeap.Buffer.First();
if (DGt(destination.TravelingCosts.From(toExpand), destination.TravelingCosts.From(farthestResult)))
{
// the closest candidate is farther than farthest result
break;
}
// expand candidate
foreach (var neighbour in toExpand.GetConnections(level))
{
if (!visited.Contains(neighbour.Id))
{
// enque perspective neighbours to expansion list
farthestResult = resultHeap.Buffer.First();
if (resultHeap.Buffer.Count < k ||
DLt(destination.TravelingCosts.From(neighbour), destination.TravelingCosts.From(farthestResult)))
{
expansionHeap.Push(neighbour);
resultHeap.Push(neighbour);
if (resultHeap.Buffer.Count > k)
{
resultHeap.Pop();
}
}
// update visited list
visited.Add(neighbour.Id);
}
}
}
return(resultHeap.Buffer);
}
/// <inheritdoc />
public override IList <Node> SelectBestForConnecting(IList <Node> candidates)
{
/*
* q ← this
* R ← ∅ // result
* W ← C // working queue for the candidates
* if expandCandidates // expand candidates
* for each e ∈ C
* for each eadj ∈ neighbourhood(e) at layer lc
* if eadj ∉ W
* W ← W ⋃ eadj
*
* Wd ← ∅ // queue for the discarded candidates
* while │W│ gt 0 and │R│ lt M
* e ← extract nearest element from W to q
* if e is closer to q compared to any element from R
* R ← R ⋃ e
* else
* Wd ← Wd ⋃ e
*
* if keepPrunedConnections // add some of the discarded connections from Wd
* while │Wd│ gt 0 and │R│ lt M
* R ← R ⋃ extract nearest element from Wd to q
*
* return R
*/
IComparer <Node> closerIsLess = this.TravelingCosts;
IComparer <Node> fartherIsLess = closerIsLess.Reverse();
var resultHeap = new BinaryHeap <Node>(new List <Node>(GetM(this.Parameters.M, this.MaxLevel) + 1), closerIsLess);
var candidatesHeap = new BinaryHeap <Node>(candidates, fartherIsLess);
// expand candidates option is enabled
if (this.Parameters.ExpandBestSelection)
{
var candidatesIds = new HashSet <int>(candidates.Select(c => c.Id));
foreach (var neighbour in this.GetConnections(this.MaxLevel))
{
if (!candidatesIds.Contains(neighbour.Id))
{
candidatesHeap.Push(neighbour);
candidatesIds.Add(neighbour.Id);
}
}
}
// main stage of moving candidates to result
var discardedHeap = new BinaryHeap <Node>(new List <Node>(candidatesHeap.Buffer.Count), fartherIsLess);
while (candidatesHeap.Buffer.Any() && resultHeap.Buffer.Count < GetM(this.Parameters.M, this.MaxLevel))
{
var candidate = candidatesHeap.Pop();
var farestResult = resultHeap.Buffer.FirstOrDefault();
if (farestResult == null ||
DLt(this.TravelingCosts.From(candidate), this.TravelingCosts.From(farestResult)))
{
resultHeap.Push(candidate);
}
else if (this.Parameters.KeepPrunedConnections)
{
discardedHeap.Push(candidate);
}
}
// keep pruned option is enabled
if (this.Parameters.KeepPrunedConnections)
{
while (discardedHeap.Buffer.Any() && resultHeap.Buffer.Count < GetM(this.Parameters.M, this.MaxLevel))
{
resultHeap.Push(discardedHeap.Pop());
}
}
return(resultHeap.Buffer);
}
/// <inheritdoc/>
internal override List <int> SelectBestForConnecting(List <int> candidatesIds, TravelingCosts <int, TDistance> travelingCosts, int layer)
{
/*
* q ← this
* R ← ∅ // result
* W ← C // working queue for the candidates
* if expandCandidates // expand candidates
* for each e ∈ C
* for each eadj ∈ neighbourhood(e) at layer lc
* if eadj ∉ W
* W ← W ⋃ eadj
*
* Wd ← ∅ // queue for the discarded candidates
* while │W│ gt 0 and │R│ lt M
* e ← extract nearest element from W to q
* if e is closer to q compared to any element from R
* R ← R ⋃ e
* else
* Wd ← Wd ⋃ e
*
* if keepPrunedConnections // add some of the discarded connections from Wd
* while │Wd│ gt 0 and │R│ lt M
* R ← R ⋃ extract nearest element from Wd to q
*
* return R
*/
IComparer <int> fartherIsOnTop = travelingCosts;
IComparer <int> closerIsOnTop = fartherIsOnTop.Reverse();
var layerM = GetM(layer);
var resultHeap = new BinaryHeap <int>(new List <int>(layerM + 1), fartherIsOnTop);
var candidatesHeap = new BinaryHeap <int>(candidatesIds, closerIsOnTop);
// expand candidates option is enabled
if (GraphCore.Parameters.ExpandBestSelection)
{
var visited = new HashSet <int>(candidatesHeap.Buffer);
var toAdd = new HashSet <int>();
foreach (var candidateId in candidatesHeap.Buffer)
{
var candidateNeighborsIDs = GraphCore.Nodes[candidateId][layer];
foreach (var candidateNeighbourId in candidateNeighborsIDs)
{
if (!visited.Contains(candidateNeighbourId))
{
toAdd.Add(candidateNeighbourId);
visited.Add(candidateNeighbourId);
}
}
}
foreach (var id in toAdd)
{
candidatesHeap.Push(id);
}
}
// main stage of moving candidates to result
var discardedHeap = new BinaryHeap <int>(new List <int>(candidatesHeap.Buffer.Count), closerIsOnTop);
while (candidatesHeap.Buffer.Any() && resultHeap.Buffer.Count < layerM)
{
var candidateId = candidatesHeap.Pop();
var farestResultId = resultHeap.Buffer.FirstOrDefault();
if (!resultHeap.Buffer.Any() || DistanceUtils.LowerThan(travelingCosts.From(candidateId), travelingCosts.From(farestResultId)))
{
resultHeap.Push(candidateId);
}
else if (GraphCore.Parameters.KeepPrunedConnections)
{
discardedHeap.Push(candidateId);
}
}
// keep pruned option is enabled
if (GraphCore.Parameters.KeepPrunedConnections)
{
while (discardedHeap.Buffer.Any() && resultHeap.Buffer.Count < layerM)
{
resultHeap.Push(discardedHeap.Pop());
}
}
return(resultHeap.Buffer);
}
/// <summary>
/// Creates a descending key comparer.
/// </summary>
/// <typeparam name="TKey">The type of key objects being compared.</typeparam>
/// <param name="selector">The key selector. May not be <c>null</c>.</param>
/// <param name="keyComparer">The key comparer. The returned comparer applies this key comparer in reverse. Defaults to <c>null</c>. If this is <c>null</c>, the default comparer is used.</param>
/// <param name="allowNulls">A value indicating whether <c>null</c> values are passed to <paramref name="selector"/>. If <c>false</c>, then <c>null</c> values are considered less than any non-<c>null</c> values and are not passed to <paramref name="selector"/>.</param>
/// <returns>A key comparer.</returns>
public static IFullComparer <T> OrderByDescending <TKey>(Func <T, TKey> selector, IComparer <TKey> keyComparer = null, bool allowNulls = false)
{
Contract.Requires(selector != null);
Contract.Ensures(Contract.Result <IFullComparer <T> >() != null);
return(OrderBy <TKey>(selector, keyComparer.Reverse(), allowNulls));
}
