I have a list of integer lists, like that:
A -> 10 10 1 1 1
B -> 10 9 9 7 6
...
I would like to sort them based on how many 10s they have, then on how many 9s, 8s, 7s, and so on untile the 1s
So in the example above A should be better than B because even if it has less total points, it has two 10s instead of only 1.
Code should be generic because I don't know how many numbers will be available for each case (sometimes 10, sometimes 5, or even only 3).
I developed something like that:
lists.OrderByDescending(a => a.Where(b => b == 10).Count()).
ThenByDescending(a => a.Where(b => b == 9).Count()).
and so on, but this is not generic...
I hope the question is clear... thank you very much!
You can create query which orders lists by count of 10s, then compose query by adding additional orderings for numbers from 9 to 1:
var query = lists.OrderByDescending(l => l.Count(x => x == 10));
for (int i = 9; i >= 1; i--)
query = query.ThenByDescending(l => l.Count(x => x == i));
For these sample lists:
var lists = new[] {
new[] { 10, 9, 9, 8, 7 },
new[] { 10, 9, 9, 7, 6 },
new[] { 10, 10, 1, 1, 1 }
};
Result will be:
[10, 10, 1, 1, 1]
[10, 9, 9, 8, 7]
[10, 9, 9, 7, 6]
It's simple, but not very efficient. If you need better performance, then consider creating custom comparer. Here is sample with comparer which uses zipped ordered sequences to check if all items in sequences are same, or get first item which is different:
public class CustomComparer : Comparer<IList<int>>
{
public override int Compare(IList<int> x, IList<int> y)
{
var comparisons = x.Zip(y, (a,b) => a.CompareTo(b));
foreach(var comparison in comparisons)
{
if (comparison != 0)
return comparison;
}
return x.Count.CompareTo(y.Count);
}
}
NOTE: If items in lists are not ordered, then you should sort them before zipping:
var comparisons =
x.OrderByDescending(i => i)
.Zip(y.OrderByDescending(i => i), (a,b) => a.CompareTo(b));
It works very simple. Consider two lists:
[10, 9, 9, 8, 7, 5]
[10, 9, 9, 7, 6]
It will create pairs of items in corresponding positions:
{10,10}, {9,9}, {9,9}, {8,7}, {7,6}
Then items in each pair will be compared one by one, until first mismatch will be found:
0, 0, 0, 1 (four comparisons only)
That means first list has more 8s than second one. Usage:
var query = lists.OrderByDescending(i => i, new CustomComparer());
Result is same.
The following comparer
public class Comparer : IComparer<IEnumerable<int>>
{
public int Compare(IEnumerable<int> a, IEnumerable<int> b)
{
var aOrdered = a.OrderByDescending(i => i).Concat(new[] { int.MinValue });
var bOrdered = b.OrderByDescending(i => i).Concat(new[] { int.MinValue });
return a.Zip(b, (i, j) => i.CompareTo(j)).FirstOrDefault(c => c != 0);
}
}
lets you order you lists of lists like so
var result = lists.OrderByDescending(i => i, new Comparer());
without iterating through each list ten times counting individual elements.
This compares the lists and returns conventional comparison result - 1, 0, or -1 is returned depending on whether one value is greater than, equal to, or less than the other.
static int CompareLists(List<int> a, List<int> b)
{
var grpA = a.GroupBy(p => p).ToDictionary(k=>k.Key,v=>v.Count());
var grpB = b.GroupBy(p => p).ToDictionary(k=>k.Key,v=>v.Count());
for (int i = 10; i >= 0; i--)
{
int countA = grpA.ContainsKey(i) ? grpA[i] : 0;
int countB = grpB.ContainsKey(i) ? grpB[i] : 0;
int comparison = countA.CompareTo(countB);
if (comparison != 0)
return comparison;
}
return 0;
}
First we convert the lists into dictionary of number->amount of occurences.
Then we iterate through numbers from 10 to 0 and compare the number of occurences. If the result is 0, then we go to another number.
If you have List<List<int>> to sort, just use list.Sort(CompareLists) as in:
List<int> d = new List<int> { 10, 6, 6 };
List<int> b = new List<int> { 10, 9, 9 };
List<int> a = new List<int> { 10, 10, 1, 1, 1 };
List<int> c = new List<int> { 10, 7, 7 };
List<int> e = new List<int> { 9, 3, 7 };
List<int> f = new List<int> { 9, 9, 7 };
List<List<int>> list = new List<List<int>>() { a, b, c, d, e, f };
list.Sort(CompareLists);
Related
I have a list of items (not sure they are even or odd number of items). What I wanna do is, pick up records in the pair of 5 (which actually is a list), create another list and insert these pair of 5 lists into that new list.
Thanks
I can create a group of items by doing this
MyList
.Zip(Enumerable.Range(0, MyList.Count()),
(s, r) => new {
Group = r / 5,
Item = s })
.GroupBy(i => i.Group,
g => g.Item)
.ToList();
But I want to generate a nested list.
Not sure I understand your aim correctly, but you can try to use Dictionary for it:
MyList.Zip(Enumerable.Range(0, MyList.Count()),
(s, r) => new { Group = r / 5, Item = s })
.GroupBy(i => i.Group, g => g.Item)
.ToDictionary(g => g.Key, g => g.ToList());
It looks like you want to batch elements in batches of 5 items each. The MoreLinq package already offers the Batch operator for this:
var items=Enumerable.Range(0,17);
var batches=items.Batch(5);
foreach(var batch in batches)
{
Console.WriteLine(String.Join(" - ",batch));
}
This produces :
0 - 1 - 2 - 3 - 4
5 - 6 - 7 - 8 - 9
10 - 11 - 12 - 13 - 14
15 - 16
This is far faster than grouping as it only iterates the collection once.
MoreLINQ has other operators too, like Window, WindowLeft and WindowRight that produce sliding windows of values. items.Window(5) would produce :
0 - 1 - 2 - 3 - 4
1 - 2 - 3 - 4 - 5
...
11 - 12 - 13 - 14 - 15
12 - 13 - 14 - 15 - 16
The implementation
The operator's implementation is simple enough that you can just copy it into your project:
public static IEnumerable<IEnumerable<TSource>> Batch<TSource>(this IEnumerable<TSource> source, int size)
{
return Batch(source, size, x => x);
}
public static IEnumerable<TResult> Batch<TSource, TResult>( IEnumerable<TSource> source, int size,
Func<IEnumerable<TSource>, TResult> resultSelector)
{
if (source == null) throw new ArgumentNullException(nameof(source));
if (size <= 0) throw new ArgumentOutOfRangeException(nameof(size));
if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
return _(); IEnumerable<TResult> _()
{
TSource[] bucket = null;
var count = 0;
foreach (var item in source)
{
if (bucket == null)
{
bucket = new TSource[size];
}
bucket[count++] = item;
// The bucket is fully buffered before it's yielded
if (count != size)
{
continue;
}
yield return resultSelector(bucket);
bucket = null;
count = 0;
}
// Return the last bucket with all remaining elements
if (bucket != null && count > 0)
{
Array.Resize(ref bucket, count);
yield return resultSelector(bucket);
}
}
}
The code uses arrays for efficiency. If you really want to use mutable lists you can change the type of bucket to a List<T>, eg :
if (bucket == null)
{
bucket = new List<TSource>(size); //IMPORTANT: set the capacity to avoid reallocations
}
bucket.Add(item);
...
Why not just GroupBy?
using System.Linq;
...
int groupSize = 5;
var result = MyList
.Select((item, index) => new {
item,
index
})
.GroupBy(pair => pair.index / groupSize,
pair => pair.item)
.Select(group => group.ToList())
.ToList();
If you have a collection of items
var items = Enumerable.Range(1, 20);
And you want to take, say, 5 at a time
var setSize = 5;
You can iterate over the collection by index, and take that 5 at a time as a list, and put all those lists of 5 into one outer list
Enumerable.Range(0, items.Count() - setSize).Select(x => items.Skip(x).Take(setSize).ToList()).ToList()
The result (from C# interactive shell) looks like
List<List<int>>(15) {
List<int>(5) { 1, 2, 3, 4, 5 },
List<int>(5) { 2, 3, 4, 5, 6 },
List<int>(5) { 3, 4, 5, 6, 7 },
List<int>(5) { 4, 5, 6, 7, 8 },
List<int>(5) { 5, 6, 7, 8, 9 },
List<int>(5) { 6, 7, 8, 9, 10 },
List<int>(5) { 7, 8, 9, 10, 11 },
List<int>(5) { 8, 9, 10, 11, 12 },
List<int>(5) { 9, 10, 11, 12, 13 },
List<int>(5) { 10, 11, 12, 13, 14 },
List<int>(5) { 11, 12, 13, 14, 15 },
List<int>(5) { 12, 13, 14, 15, 16 },
List<int>(5) { 13, 14, 15, 16, 17 },
List<int>(5) { 14, 15, 16, 17, 18 },
List<int>(5) { 15, 16, 17, 18, 19 }
}
If you want each item to only show up once in each list, you can alter the above. Let's assume there's an odd number of elements:
var items = Enumerable.Range(1, 11);
You want to change the initial range used to index into your collection. Instead of taking 5 at a time on each index, it will jump the index up by 5 each iteration. The only tricky part is making sure to handle when the collection divides the number of elements you want to take; you don't want to end up with an empty list at the end. That is, this is incorrect:
Enumerable.Range(0, items.Count() / setSize).Select( // don't do this
The statement is then
Enumerable.Range(0, ((items.Count() - 1) / setSize) + 1).Select(x => items.Skip(setSize * x).Take(setSize).ToList()).ToList();
The result (from C# interactive shell) looks like
List<List<int>>(3) {
List<int>(5) { 1, 2, 3, 4, 5 },
List<int>(5) { 6, 7, 8, 9, 10 },
List<int>(1) { 11 }
}
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]);
}
I need to find a way to return the longest match found in number of sets/lists (values returns only once) when the order of items is important.
the list is not cyclic.
A match is a sequence of values that exists in all the lists and maintains the same order of elements in all the lists.
e.g. 1:
List<int> list1 = new List<int> { 1, 2, 3, 4, 7, 9 };
List<int> list2 = new List<int> { 1, 2, 5, 6, 3, 4, 7, 9 };
List<int> list3 = new List<int> { 1, 2, 3, 6, 8, 9 };
List<int> list4 = new List<int> { 1, 2, 5, 6, 8, 9 };
result { 1, 2 }
e.g. 2:
List<int> list1 = new List<int> { 2, 3, 6, 8, 1, 18 };
List<int> list2 = new List<int> { 2, 3, 4, 6, 8, 1, 18, 19, 17, 14 };
List<int> list3 = new List<int> { 2, 5, 6, 8, 1, 18, 16, 13, 14 };
List<int> list4 = new List<int> { 2, 6, 8, 1, 18, 19, 17, 14 };
result { 6, 8, 1, 18 }
The match doesn't have to be found at the beginning or at the end and can be on any part of any list.
I hope that I explained my problem good enough :)
Thanks!
You can build a map from pairs of ints to a count of how many of the lists they appear adjacent in.
Pseudo-code:
For each list L {
For each adjacent pair (x, y) in L {
Counts[x, y] += 1
}
}
Now you can iterate through the first list (or the shortest list), and find the longest run such that each adjacent pair (x, y) in the run with Counts[x, y] showing that the pair appears in every list.
Pseudo-code:
run = []
best_run = []
For x in L[0] {
if len(run) is zero or Counts[run[len(run)-1], x] == number of lists {
run = run + x
} else {
run = [x]
}
if run is longer than best_run {
best_run = run
}
}
This works given the assumption in the question that no integer appears twice in the same list.
This algorithm runs in O(N) time, where N is the sum of the lengths of all the lists.
Here's my approach.
First I need a way to compare lists:
public class ListCompare<T> : IEqualityComparer<List<T>>
{
public bool Equals(List<T> left, List<T> right)
{
return left.SequenceEqual(right);
}
public int GetHashCode(List<T> list)
{
return list.Aggregate(0, (a, t) => a ^ t.GetHashCode());
}
}
Next a method to produce all subsequences of a source list:
Func<List<int>, IEnumerable<List<int>>> subsequences = xs =>
from s in Enumerable.Range(0, xs.Count)
from t in Enumerable.Range(1, xs.Count - s)
select xs.Skip(s).Take(t).ToList();
Now I can create a list of lists:
var lists = new [] { list1, list2, list3, list4, };
Finally a query that pulls it all together:
var answer =
lists
.Skip(1)
.Aggregate(
subsequences(lists.First()),
(a, l) => a.Intersect(subsequences(l), new ListCompare<int>()))
.OrderByDescending(x => x.Count)
.FirstOrDefault();
Given the sample data provided in the question this produces the expected results.
First generate an ordered combination of int from the shortest list
Compare the lists other than shortest list with the combination. For easy comparison of lists I just convert to string and use string.Contains()
Return immediately if find the match as the items left are next order or the shorter one.
public static List<int> GetLongestMatch(params List<int>[] all)
{
var shortest = all.Where(i => i.Count == all.Select(j => j.Count).Min()).First();
var permutations = (from length in Enumerable.Range(1, shortest.Count)
orderby length descending
from count in Enumerable.Range(1, shortest.Count - length + 1)
select shortest.Skip(count - 1).Take(length).ToList())
.ToList();
Func<List<int>, string> stringfy = (list) => { return string.Join(",", list.Select(i => i.ToString()).ToArray()); };
foreach (var item in permutations)
{
Debug.WriteLine(string.Join(", ", item.Select(i => i.ToString()).ToArray()));
if (all.All(list => stringfy(list).Contains(stringfy(item))))
{
Debug.WriteLine("Matched, skip process and return");
return item;
}
}
return new List<int>();
}
Usage
var result = GetLongestMatch(list1, list2, list3, list4);
Result
2, 3, 6, 8, 1, 18
2, 3, 6, 8, 1
3, 6, 8, 1, 18
2, 3, 6, 8
3, 6, 8, 1
6, 8, 1, 18
Matched, skip process and return
I want to find the top 3 maximum repeated numbers in a Integer array?
Below is the piece of code which I have tried but I couldn't find the desired result:
static void Main(string[] args)
{
int[,] numbers = {
{1, 2, 0, 6 },
{5, 6, 7, 0 },
{9, 3, 6, 2 },
{6, 4, 8, 1 }
};
int count = 0;
List<int> checkedNumbers = new List<int>();
foreach (int t in numbers)
{
if (!checkedNumbers.Contains(t))
{
foreach (int m in numbers)
{
if (m == t)
{
count++;
}
}
Console.WriteLine("Number {0} is Repeated {1} Times ", t, count);
count = 0;
checkedNumbers.Add(t);
}
}
Console.ReadLine();
}
You can use GroupBy from LINQ then OrderByDescending based on count in each group:
var result = list.GroupBy(i => i)
.OrderByDescending(g => g.Count())
.Select(g => g.Key)
.Take(3);
Edit: With your code, you can use OfType to flatten your matrix then use the code above:
int[,] numbers = {
{1, 2, 0, 6 },
{5, 6, 7, 0 },
{9, 3, 6, 2 },
{6, 4, 8, 1 }
};
var list = numbers.OfType<int>();
int[] numbers = {1, 2, 3, 5, 6, 32, 2, 4, 42, 2, 4, 4, 5, 6, 3, 4};
var counts = new Dictionary<int, int>();
foreach (var number in numbers)
{
counts[number] = counts[number] + 1;
}
var top3 = counts.OrderByDescending(x => x.Value).Select(x => x.Key).Take(3);
Hint:
You can do this with the help of LINQ.
This is the code to find most frequest occuring element:-
List<int> list = new List<int>() { 1,1,2,2,3,4,5 };
// group by value and count frequency
var query = from i in list
group i by i into g
select new {g.Key, Count = g.Count()};
// compute the maximum frequency
int frequency = query.Max(g => g.Count);
// find the values with that frequency
IEnumerable<int> modes = query
.Where(g => g.Count == frequency)
.Select(g => g.Key);
// dump to console
foreach(var mode in modes) {
Console.WriteLine(mode);
}
In the same manner you can find the other two also.
I see that none of the existing answers provide an explanation, so I will try to explain.
What you need to do is to count how many times each item appears in the array. To do that, there are various methods (dictionaries, linq etc). Probably it would be easiest to use a dictionary which contains the number, and how may times it appeared:
int numbers[] = {1, 3, 6, 10, 9, 3, 3, 1, 10} ;
Dictionary<int, int> dic = new Dictionary<int, int>();
Now iterate through every element in numbers, and add it to the dictionary. If it was already added, simply increase the count value.
foreach (var i in numbers)
{
dic[i]++; // Same as dic[i] = dic[i]+1;
}
The dictionary will automatically adds a new item if it doesn't exist, so we can simply do dic[i]++;
Next, we need to get the highest 3 values. Again, there are many ways to do this, but the easiest one would be to sort it.
var sorted_dic = dic.OrderByDescending(x => x.Value);
Now the first 3 items in sorted_dic are going to be the 3 values you are looking for.
There are various methods to get only these 3, for example using the Take method:
var first_3 = sorted_dic.Take(3);
Now you can iterate through these 3 values, and for example print them on the screen:
foreach (var i in first_3)
{
Console.Write("{0} appeared {1} times.", i.Key, i.Value);
}
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) } );