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using System.Collections.Generic;
using System;
namespace Langexplr.Experiments
{
public class MyTuple<T,K>
{
public T Item1 { get; set; }
public K Item2 { get; set; }
public static MyTuple<T1,K1> Create<T1,K1>(T1 first, K1 second)
{
return new MyTuple<T1,K1>() {Item1 = first, Item2 = second};
}
}
public static class GroupByTests
{
public static IEnumerable<MyTuple<T,IEnumerable<T>>> MyGroupBy<T>(this IEnumerable<T> en)
{
return MyGroupBy(en,x => x);
}
public static IEnumerable<MyTuple<K,IEnumerable<T>>> MyGroupBy<T,K>(this IEnumerable<T> en,Func<T,K> keyExtraction)
{
K currentGroupKey = default(K);
bool firstTime = true;
bool hasMoreElements = false;
bool yieldNewValue = false;
IEnumerator<T> enumerator = en.GetEnumerator();
hasMoreElements = enumerator.MoveNext();
while (hasMoreElements)
{
if (firstTime)
{
firstTime = false;
yieldNewValue = true;
currentGroupKey = keyExtraction(enumerator.Current);
}
else
{
K lastKey;
while((lastKey = keyExtraction(enumerator.Current)).Equals( currentGroupKey) &&
(hasMoreElements = enumerator.MoveNext()))
{
}
if(hasMoreElements &&
!lastKey.Equals(currentGroupKey))
{
currentGroupKey = lastKey;
yieldNewValue = true;
}
else
{
yieldNewValue = false;
}
}
if (yieldNewValue) {
yield return MyTuple<K,IEnumerable<T>>.Create(
currentGroupKey,
ReturnSubSequence((x) => {
hasMoreElements = enumerator.MoveNext();
return hasMoreElements &&
x.Equals(keyExtraction(enumerator.Current)); },enumerator,
currentGroupKey,
enumerator.Current));
}
}
}
static IEnumerable<T> ReturnSubSequence<T,K>(Predicate<K> pred, IEnumerator<T> seq,K currentElement,T first)
{
yield return first;
while( pred(currentElement))
{
yield return seq.Current;
}
}
public static IEnumerable<MyTuple<T,IList<T>>> MyGroupByWithLists<T>(this IEnumerable<T> enumerable)
{
return MyGroupByWithLists(enumerable, x => x);
}
public static IEnumerable<MyTuple<K,IList<T>>> MyGroupByWithLists<T,K>(this IEnumerable<T> en,Func<T,K> keyExtraction)
{
K currentKey = default(K);
bool firstTime = true;
IList<T> currentGroup = new List<T>();
foreach(var aValue in en)
{
if (firstTime)
{
currentKey = keyExtraction(aValue);
firstTime = false;
}
else
{
K tmpKey = keyExtraction(aValue);
if (!tmpKey.Equals(currentKey))
{
yield return MyTuple<K,IList<T>>.Create(currentKey, currentGroup);
currentGroup = new List<T>();
currentKey = tmpKey;
}
}
currentGroup.Add(aValue);
}
if (currentGroup.Count > 0)
{
yield return MyTuple<K,IList<T>>.Create(currentKey, currentGroup);
}
}
}
}
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