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I have Two lists of type list<int> and i know we can find the common elements between two lists. But is there any way to get common elements and corresponding indexes of common elements in Intersected list or i need to go across each elements find the indexes.
LINQ has operations to project a sequence using indexes, but this isn't built into the query expression syntax, so you have to use "regular" extension method calls to start with. After that it's fairly easy, although probably just as simple not using LINQ, to be honest:
var pairs1 = list1.Select((value, index) => new { value, index });
var pairs2 = list2.Select((value, index) => new { value, index });
var matches = from pair1 in pairs1
join pair2 in pairs2 on pair1.value equals pair2.value
select new
{
Value = pair1.value,
Index1 = pair1.index,
Index2 = pair2.index
};
(You could use from pair2 in pairs2 where pair1.value == pair2.value if you'd prefer...)
Or non-LINQ (using Tuple<,,> for simplicity; other options are feasible):
var results = new List<Tuple<int, int, int>>();
for (int index1 = 0; index1 < list1.Count; index1++)
{
for (int index2 = 0; index2 < list2.Count; index2++)
{
if (list1[index1] == list2[index2])
{
results.Add(Tuple.Of(list1[index1], index1, index2);
}
}
}
Note that unlike a regular intersection operation, both of these can give you multiple results for the same value - because there can be multiple index pairs. For example, with lists of { 1, 2 } and {2, 2, 0}, you'd have tuples of (value=2,index1=1,index2=0), (value=2,index1=1,index2=1).
try below code
List<int> lstA = new List<int>() { 10, 2, 7, 9, 13, 21, 17 };
List<int> lstB = new List<int>() { 2, 10, 7, 21, 13, 9, 17 };
var lstA_Temp = lstA.Select((value, index) => new { index, value }).ToList();
var lstB_Temp = lstB.Select((value, index) => new { index, value }).ToList();
List<int> result = (from A in lstA_Temp from B in lstB_Temp
where A.index == B.index where A.value == B.value
select A.value).ToList();
you can also do this thing without linq see below logic
List<int> lstA = new List<int>() { 10, 2, 7, 9, 13, 21, 17 };
List<int> lstB = new List<int>() { 2, 10, 7, 21, 13, 9, 17 };
List<int> lstResult = new List<int>();
for (int i = 0; i < lstA.Count; i++)
{
if (lstA[i] == lstB[i])
lstResult.Add(lstA[i]);
}
The current problem is that the code works, but it gets exponentially slower as more combinations are passed in. (The calculation takes > 5 seconds after 15 combinations are passed in.) I need to be able to pass in up to 100 combinations and still get a result back that takes less than 2 seconds.
I'm betting that a Linq query could solve this?
What I want to achieve:
{1, 2, 3} + {1, 5, 26, 40} = 12 combinations:
[1,1]
[1,5]
[1,26]
[1,40]
[2,1]
[2,5]
[2,26]
[2,40]
[3,1]
[3,5]
[3,26]
[3,40]
However, this example above only includes 2 combination sets. I should be able to pass in any number of combination sets.
The closest thing that looks like it is similar to what I want as an end result, due to being fast and efficient, is a linq query that handles most or all of the logic within it. Example: Getting all possible combinations from a list of numbers
public IEnumerable<IEnumerable<T>> GetPowerSet<T>(List<T> list)
{
return from m in Enumerable.Range(0, 1 << list.Count)
select
from i in Enumerable.Range(0, list.Count)
where (m & (1 << i)) != 0
select list[i];
}
Example of working code:
[Test]
public void StackOverflowExample_Simple()
{
var list1 = new List<int>() { 1, 2, 3 };
var list2 = new List<int>() { 1, 5, 26, 40 };
var myListsOfNumberCombinations = new List<List<int>>() { list1, list2 };
var results = GetAllPossibleCombinations(myListsOfNumberCombinations);
Assert.AreEqual(12, results.Count());
StringBuilder sb = new StringBuilder();
foreach (var result in results)
{
foreach (var number in result.OrderBy(x => x))
{
sb.Append(number + ",");
}
sb.Append("|");
}
string finalResult = sb.ToString().Replace(",|", "|");
Assert.AreEqual(finalResult, "1,1|1,5|1,26|1,40|1,2|2,5|2,26|2,40|1,3|3,5|3,26|3,40|");
}
[Test]
public void StackOverflowExample_TakesALongTime()
{
var list1 = new List<int>() { 1, 2, 3 };
var list2 = new List<int>() { 4, 5 };
var list3 = new List<int>() { 1, 6 };
var list4 = new List<int>() { 2, 5 };
var list5 = new List<int>() { 1, 3, 55, 56 };
var list6 = new List<int>() { 3, 4, 7, 8, 9 };
var myListsOfNumberCombinations = new List<List<int>>() { list1, list2, list3, list4, list5, list1, list1, list1, list3, list4, list4, list5, list6, list6, list2 };
DateTime startTime = DateTime.Now;
var results = GetAllPossibleCombinations(myListsOfNumberCombinations);
Assert.AreEqual(4147200, results.Count());
var duration = DateTime.Now.Subtract(startTime).TotalSeconds;
//duration = about 4 or 5 seconds
Assert.Less(duration, 10); //easy place to put a breakpoint
}
public IEnumerable<IEnumerable<int>> GetAllPossibleCombinations(List<List<int>> combinationSets)
{
List<List<int>> returnList = new List<List<int>>();
_RecursiveGetMoreCombinations(
ref returnList,
new List<int>(),
combinationSets,
0);
return returnList;
}
private void _RecursiveGetMoreCombinations(
ref List<List<int>> returnList,
List<int> appendedList,
List<List<int>> combinationSets,
int index)
{
var combinationSet = combinationSets[index];
foreach (var number in combinationSet)
{
List<int> newList = appendedList.AsEnumerable().ToList();
newList.Add(number);
if (combinationSets.Count() == index + 1)
{
returnList.Add(newList);
}
else
{
_RecursiveGetMoreCombinations(
ref returnList,
newList,
combinationSets,
index + 1);
}
}
}
Can you not just do permutations of the first and third sets (the OR sets) and then place '45' (the AND set), or whatever the static numbers are, in between those numbers?
You don't need to include 4 and 5 (in this example) in the permutation logic if they are always going to be present.
I have two sorted lists as below:
var list1 = new List<int>() { 1, 1, 1, 2, 3 };
var list2 = new List<int>() { 1, 1, 2, 2, 4 };
I want the output to be: {1, 1, 2}
How to do this in C#?
Is there a way using Linq?
Use Intersect:
var commonElements = list1.Intersect(list2).ToList();
The extra 1 means you can't use Intersect because it returns a set.
Here's some code that does what you need:
var list1 = new List<int>() { 1, 1, 1, 2, 3 };
var list2 = new List<int>() { 1, 1, 2, 2, 4 };
var grouped1 =
from n in list1
group n by n
into g
select new {g.Key, Count = g.Count()};
var grouped2 =
from n in list2
group n by n
into g
select new {g.Key, Count = g.Count()};
var joined =
from b in grouped2
join a in grouped1 on b.Key equals a.Key
select new {b.Key, Count = Math.Min(b.Count, a.Count)};
var result = joined.SelectMany(a => Enumerable.Repeat(a.Key, a.Count));
CollectionAssert.AreEquivalent(new[] {1, 1, 2}, result);
This works nicely:
var list1 = new List<int>() { 1, 1, 1, 2, 3 };
var list2 = new List<int>() { 1, 1, 2, 2, 4 };
var lookup1 = list1.ToLookup(x => x);
var lookup2 = list2.ToLookup(x => x);
var results = lookup1.SelectMany(l1s => lookup2[l1s.Key].Zip(l1s, (l2, l1) => l1));
While both #Austin Salonen's solution and #Enigmativity's solution work for any given lists, neither take advantage of OP's condition that the lists are sorted.
Given that both lists will be ordered we can do a search in O(n + m) time where n and m are the length of each list. Not entirely sure what the previous solutions big o performance is, but it's definitely slower then O(n + m).
Basically we just walk both lists, moving one or both enumerators based on a comparison check.
var results = new List<int>();
var e1 = list1.GetEnumerator();
var e2 = list2.GetEnumerator();
var hasNext = e1.MoveNext() && e2.MoveNext();
while (hasNext) {
var value1 = e1.Current;
var value2 = e2.Current;
if (value1 == value2) {
results.Add(value1);
hasNext = e1.MoveNext() && e2.MoveNext();
} else if (value1 < value2) {
hasNext = e1.MoveNext();
} else if (value1 > value2) {
hasNext = e2.MoveNext();
}
}
That's it! results will be an empty list if no matches are found.
Note this assumes both lists are in ascending order. If it's descending, just flip the < and > operators.
I am late in answering this question, this might help future visitors.
List<int> p = new List<int> { 1, 1, 1, 2, 3 };
List<int> q = new List<int> { 1, 1, 2, 2, 4 };
List<int> x = new List<int>();
for (int i = 0; i < p.Count; i++ )
{
if (p[i] == q[i])
{
x.Add(p[i]);
}
}
Last night I had dream that the following was impossible. But in the same dream, someone from SO told me otherwise. Hence I would like to know if it it possible to convert System.Array to List
Array ints = Array.CreateInstance(typeof(int), 5);
ints.SetValue(10, 0);
ints.SetValue(20, 1);
ints.SetValue(10, 2);
ints.SetValue(34, 3);
ints.SetValue(113, 4);
to
List<int> lst = ints.OfType<int>(); // not working
Save yourself some pain...
using System.Linq;
int[] ints = new [] { 10, 20, 10, 34, 113 };
List<int> lst = ints.OfType<int>().ToList(); // this isn't going to be fast.
Can also just...
List<int> lst = new List<int> { 10, 20, 10, 34, 113 };
or...
List<int> lst = new List<int>();
lst.Add(10);
lst.Add(20);
lst.Add(10);
lst.Add(34);
lst.Add(113);
or...
List<int> lst = new List<int>(new int[] { 10, 20, 10, 34, 113 });
or...
var lst = new List<int>();
lst.AddRange(new int[] { 10, 20, 10, 34, 113 });
There is also a constructor overload for List that will work... But I guess this would required a strong typed array.
//public List(IEnumerable<T> collection)
var intArray = new[] { 1, 2, 3, 4, 5 };
var list = new List<int>(intArray);
... for Array class
var intArray = Array.CreateInstance(typeof(int), 5);
for (int i = 0; i < 5; i++)
intArray.SetValue(i, i);
var list = new List<int>((int[])intArray);
Interestingly no one answers the question, OP isn't using a strongly typed int[] but an Array.
You have to cast the Array to what it actually is, an int[], then you can use ToList:
List<int> intList = ((int[])ints).ToList();
Note that Enumerable.ToList calls the list constructor that first checks if the argument can be casted to ICollection<T>(which an array implements), then it will use the more efficient ICollection<T>.CopyTo method instead of enumerating the sequence.
The simplest method is:
int[] ints = new [] { 10, 20, 10, 34, 113 };
List<int> lst = ints.ToList();
or
List<int> lst = new List<int>();
lst.AddRange(ints);
In the case you want to return an array of enums as a list you can do the following.
using System.Linq;
public List<DayOfWeek> DaysOfWeek
{
get
{
return Enum.GetValues(typeof(DayOfWeek))
.OfType<DayOfWeek>()
.ToList();
}
}
in vb.net just do this
mylist.addrange(intsArray)
or
Dim mylist As New List(Of Integer)(intsArray)
You can do like this basically:
int[] ints = new[] { 10, 20, 10, 34, 113 };
this is your array, and than you can call your new list like this:
var newList = new List<int>(ints);
You can do this for complex object too.
You can just give it try to your code:
Array ints = Array.CreateInstance(typeof(int), 5);
ints.SetValue(10, 0);
ints.SetValue(20, 1);
ints.SetValue(10, 2);
ints.SetValue(34, 3);
ints.SetValue(113, 4);
int[] anyVariable=(int[])ints;
Then you can just use the anyVariable as your code.
I know two methods:
List<int> myList1 = new List<int>(myArray);
Or,
List<int> myList2 = myArray.ToList();
I'm assuming you know about data types and will change the types as you please.
Just use the existing method.. .ToList();
List<int> listArray = array.ToList();
KISS(KEEP IT SIMPLE SIR)
I hope this is helpful.
enum TESTENUM
{
T1 = 0,
T2 = 1,
T3 = 2,
T4 = 3
}
get string value
string enumValueString = "T1";
List<string> stringValueList = typeof(TESTENUM).GetEnumValues().Cast<object>().Select(m =>
Convert.ToString(m)
).ToList();
if(!stringValueList.Exists(m => m == enumValueString))
{
throw new Exception("cannot find type");
}
TESTENUM testEnumValueConvertString;
Enum.TryParse<TESTENUM>(enumValueString, out testEnumValueConvertString);
get integer value
int enumValueInt = 1;
List<int> enumValueIntList = typeof(TESTENUM).GetEnumValues().Cast<object>().Select(m =>
Convert.ToInt32(m)
).ToList();
if(!enumValueIntList.Exists(m => m == enumValueInt))
{
throw new Exception("cannot find type");
}
TESTENUM testEnumValueConvertInt;
Enum.TryParse<TESTENUM>(enumValueString, out testEnumValueConvertInt);
I have the following arrays:
var original= new int[] { 2, 1, 3 };
var target = new int[] { 1, 3, 4 };
enum Operation {Added,Removed}
I would like to execute a LINQ query that would return the following:
{{2,Removed},{4,Added}}
Limitation: I would like LINQ to perform this very efficiently and avoid and O(n^2) style algorithms.
Perhaps a LINQ solution is not the best option in this case.
This will produce a dictionary with the result that you want.
Dictionary<int, Operation> difference = new Dictionary<int,Operation>();
foreach (int value in original) {
difference.Add(value, Operation.Removed);
}
foreach (int value in target) {
if (difference.ContainsKey(value)) {
difference.Remove(value);
} else {
difference.Add(value, Operation.Added);
}
}
To keep the size of the dictionary down, perhaps it's possible to loop the enumerations in parallell. I'll have a look at that...
Edit:
Here it is:
Dictionary<int, Operation> difference = new Dictionary<int,Operation>();
IEnumerator<int> o = ((IEnumerable<int>)original).GetEnumerator();
IEnumerator<int> t = ((IEnumerable<int>)target).GetEnumerator();
bool oActive=true, tActive=true;
while (oActive || tActive) {
if (oActive && (oActive = o.MoveNext())) {
if (difference.ContainsKey(o.Current)) {
difference.Remove(o.Current);
} else {
difference.Add(o.Current, Operation.Removed);
}
}
if (tActive && (tActive = t.MoveNext())) {
if (difference.ContainsKey(t.Current)) {
difference.Remove(t.Current);
} else {
difference.Add(t.Current, Operation.Added);
}
}
}
Edit2:
I did some performance testing. The first version runs 10%-20% faster, both with sorted lists and randomly ordered lists.
I made lists with numbers from 1 to 100000, randomly skipping 10% of the numbers. On my machine the first version of the code matches the lists in about 16 ms.
enum Operation { Added, Removed, }
static void Main(string[] args)
{
var original = new int[] { 2, 1, 3 };
var target = new int[] { 1, 3, 4 };
var result = original.Except(target)
.Select(i => new { Value = i, Operation = Operation.Removed, })
.Concat(
target.Except(original)
.Select(i => new { Value = i, Operation = Operation.Added, })
);
foreach (var item in result)
Console.WriteLine("{0}, {1}", item.Value, item.Operation);
}
I don't think you can do this with LINQ using only a single pass given the stock LINQ extension methods but but might be able to code a custom extension method that will. Your trade off will likely be the loss of deferred execution. It would be interesting to compare the relative performance of both.
You are out of luck. If, as you stated in the comments, the lists are not sorted you can't compute the difference you seek in a single forward pass. Consider:
{ 1, 2, 3, 4, 5, 6, 7, ...
{ 1, 2, 3, 6, 7, 8, 9, ...
At the point where the first difference in encountered (4 vs. 6) it's impossible for you to determine if you are looking at the removal of 4 & 5 (as would be the case if both lists were monotonically increasing, or the insertion of 6, 7, 8, & 9 as would be the case if the lists continued like so:
{ 1, 2, 3, 4, 5, 6, 7, 8, 9,...
{ 1, 2, 3, 6, 7, 8, 9, 4, 5, 6, 7, 8, 9,...
This will achieve the result in a single pass, however I'm not sure of the complexity of the GroupBy operation.
var original= new int[] { 1, 2, 3 };
var target = new int[] { 1, 3, 4 };
var output = original.Select( i => new { I = i, L = "o" } )
.Concat( target.Select( i => new { I = i, L = "t" } ) )
.GroupBy( i => i.I ).Where( i => i.Count() == 1 )
.Select( i => new { I = i.Key, S = (i.ElementAt( 0 ).L == "o" ? Operation.Removed : Operation.Added) } );