I have a HUGE sorted list with integers - Hugelist.
I need to create a new list of items based on input:
Query Hugelist trying to find all series of integers matching my input (variable input like: 5,6,4,9 (ideal dynamic number of inputs).
Numbers has to be in sequence in Hugelist.
Need all matched data (5,6,4,9 AND the next 7 items in Hugelist) added to new list.
So I end up with a list of matches in FilteredList
How on earth do I do this with LINQ and don't foreach my way out of it?
hugelist.OrderBy (l => l.Date)
.GroupBy (l => new { l.ID, l.City })
.ToList()
.ForEach(g => g.Aggregate (0, (acc, m) => { m.DiffToPrev = m.Value - acc; return m.Value; }));
DifftoPrev is what I would like to query with multiple inputs (ints).
You can do it like this:
List<int> input = new List<int> { 0, 0, 0, 0, 5,6,4,9, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
List<int> search = new List<int> { 5,6,4,9 };
var test = Enumerable.Range(0, input.Count - search.Count)
.Where(x => input.Skip(x)
.Take(search.Count)
.SequenceEqual(search)
)
.Select(x => input.Skip(x)
.Take(search.Count+7)
).SelectMany(x => x);
But actually, I would not do it with LINQ but with a loop, because you will iterate quite often over the list and it is not easy readable.
Online demo: https://dotnetfiddle.net/1ngzFF
Related
As the title says i have a task to find the longest repeating sequence in a string and it has to be done with linq only - no ifs, no loop, no try, assignment is only allowed on initialization of variables, recursion is allowed. I've found the solution online and i understand what is happening but i can't transform it to linq -I'm not that familiar with it. I would greatly appreciate if someone could help me. Here is a link to what ive found -https://www.javatpoint.com/program-to-find-longest-repeating-sequence-in-a-string.
List<int> a = new List<int> {1, 2, 1, 2, 1, 2, 3, 2, 1, 2};
List<List<int>> aa = new List<List<int>>();
outerLoop(a);
var max = aa.Max(x => x.Count);
var m = from v in aa
where v.Count == max
select v;
m.Dump();
void outerLoop(List<int> list)
{
List<int> f = new List<int>();
f.AddRange(list.Skip(list.Count-1).Take(list.Count).ToList());
innerLoop(list, list.Skip(1).Take(list.Count).ToList());
f.ForEach(k => outerLoop(list.Skip(1).Take(list.Count).ToList()));
}
void innerLoop(List<int> l, List<int> subList)
{
List<int> f = new List<int>();
f.AddRange(subList.Skip(subList.Count-1).Take(subList.Count).ToList());
var tt = l.TakeWhile((ch, i) => i < subList.Count && subList[i] == ch).ToList();
aa.Add(tt);
f.ForEach(k => innerLoop(l, subList.Skip(1).Take(subList.Count).ToList()));
}
so i came up with this "beauty", i don't think it's good code but i think it works. If anyone is interested and wants to make suggestions how to make it better, they are more than welcome to :)
if input is int[] x= {1, 2, 1, 2, 1, 2, 3, 2, 1, 2}
result should be 1212
Give this a go:
List<int> words = new List<int> { 1, 2, 1, 2, 1, 2, 3, 2, 1, 2 };
string result =
words
.Select((c, i) => i)
.SelectMany(i => Enumerable.Range(1, words.Count - i).Select(j => words.Skip(i).Take(j)), (i, w) => new { i, w })
.GroupBy(x => String.Join(",", x.w), x => x.i)
.Where(x => x.Skip(1).Any())
.Select(x => x.Key)
.OrderByDescending(x => x.Length)
.First();
That gives me 1,2,1,2.
If you want one that actually works with strings, try this:
var word = "supercalifragilisticexpialidocious";
string result =
word
.Select((c, i) => i)
.SelectMany(i => Enumerable.Range(1, word.Length - i).Select(j => word.Skip(i).Take(j)), (i, w) => new { i, w })
.GroupBy(x => new string(x.w.ToArray()), x => x.i)
.Where(x => x.Skip(1).Any())
.Select(x => x.Key)
.OrderByDescending(x => x.Length)
.First();
That gives me ali.
Here's a slightly more understandable version:
var word = "supercalifragilisticexpialidocious";
string result =
(
from i in Enumerable.Range(0, word.Length)
from j in Enumerable.Range(1, word.Length - i)
group i by word.Substring(i, j) into gis
where gis.Skip(1).Any()
orderby gis.Key.Length descending
select gis.Key
).First();
Here is my version. It isn't a single LINQ expression, but does use only LINQ. It does return all same length subsequences if there are multiple answers. It should work any type of sequence. It was written to only use standard LINQ methods.
It uses GroupBy with a string key to implement a sequence Distinct. (Because of this trick, lists that contain items with commas might not work right.) In production code, I would use a Distinct with an IEqualityComparer for sequences based on SequenceEqual. It also has a separate step for finding the maximum repeated sequence length and then finding all the matching sequences, in production code I would use a MaxBy extension.
Update: Since I was using GroupBy for DistinctBy, I realized I could just use that to count the subsequence repeats directly rather than search for them.
var repeaters = Enumerable.Range(0, words.Count) // starting positions
.SelectMany(n => Enumerable.Range(1, (words.Count - n) / 2).Select(l => words.Skip(n).Take(l).ToList())) // subseqs from each starting position
.GroupBy(s => String.Join(",", s), (k, sg) => new { seq = sg.First(), Repeats = sg.Count() }) // count each sequence
.Where(sr => sr.Repeats > 1) // only keep repeated sequences
.Select(sr => sr.seq); // no longer need counts
var maxRepeaterLen = repeaters.Select(ss => ss.Count()).Max(); // find longest repeated sequence's length
var maxLenRepeaters = repeaters.Where(ss => ss.Count() == maxRepeaterLen); // return all sequences matching longest length
I want the number of an array with odd occurrences.
This is my code. I think it is working but I cannot output the expected number 2 as a string. I got
System.Linq.Lookup`2+Grouping[System.Int32,System.Int32]
instead.
int[] array = { 0, 0, 1, 1, 2 };
var result = array.GroupBy(a => a)
.Select(o => o)
.Where(o => (o.Count() % 2 == 1))
.FirstOrDefault();
Console.WriteLine(result.ToString());
Try this:
var result = array.GroupBy(a => a)
.Where(o => o.Count() % 2 == 1)
.FirstOrDefault().Key;
Your approach to solving the problem is wrong, the grouped values are instances of Grouping so you have to select the appropriate values by the key.
int[] array = { 0, 0, 1, 1, 2 };
var result = array.GroupBy(a => a)
.Where(o => (o.Count() % 2 == 1))
.Select(o => o.Key);
string resultString = string.Join(", ", result.ToArray());
Console.WriteLine(resultString);
So, in this example, you should have two as the return value.
I want to sort a large integer array into 2 groups, i.e. 1 group the multiples of 4 and the other group the multiples of 5. How can I do this using just one query? Keep an eye on the performance which is really important in my case.
To further explain what I need, suppose my list of numbers is { 2, 7, 8, 10, 12, 14, 19,20, 25} then I would expect my output to be this:
new[]
{
new
{
Remainder = 4,
Numbers = new List<int>(){ 8, 12, 20}
},
new
{
Remainder = 5,
Numbers = new List<int>(){10, 20, 25}
}
}
Here's what I have gotten so far:
var numberGroupsTimes5 =
from n in numbers
group n by n % 5 into g
where g.Key == 0
select new { Remainder = g.Key, Numbers = g };
var numberGroupsTimes4 =
from n in numbers
group n by n % 4 into g
where g.Key == 0
select new { Remainder = g.Key, Numbers = g };
As you can see it gets me close with 2 queries but as I said I would like a single query.
You could use Concat:
var something = numberGroupsTimes5.Concat(numberGroupsTimes4);
to simply concatenate two sequences.
It's not entire clear why you use a GroupBy, then filter for Key == 0. Remainder will always be 0.
Maybe a simple Where is enough?
You can simply "combine" your queries by using a logical OR (||):
var something = numbers.Where(x => x%4 == 0 || x%5 == 0);
In response to your comment: Are you looking for something like this?
var result = new[] {4, 5}
.Select(d => new
{
Divider = d,
Values = numbers.Where(n => n % d == 0).ToList()
});
Do you mean?
var numberGroupsTimes4or5 = from n in numbers
group n by n into g
where g.Key % 4 == 0 || g.Key % 5 == 0
select new { Remainder = g.Key, Numbers = g };
Maybe this?
var result = new[] { 4, 5 }
.SelectMany(x => numbers.Select(n => (n, x)))
.Where(g => g.n % g.x == 0)
.GroupBy(g => g.x, (Key, g) =>
new { Remainder = Key, Numbers = g.Select(z => z.n) });
which gives this result
Here is a similar approach but this time using a query syntax like in your question.
var numbersAndRemainders = new[] { 4, 5 }
.SelectMany(rem => numbers.Select(n => (n, rem)));
var numberGroups =
from n in numbersAndRemainders
group n by new { remainder = n.n % n.rem, n.rem } into g
where g.Key.remainder == 0
select new { Remainder = g.Key.rem, Numbers = g.Select(z => z.n) };
There are two LINQ methods you could use for this:
//This will join the lists, excluding values that already appear once
var result = numberGroupsTimes5.Union(numberGroupsTimes4)
//This will simply append one list the the other
var result = numberGroupsTimes5.Concat(numberGroupsTimes4)
Suppose I have:
var correctOrder = new[] {2, 1, 0};
var actualPositionsFound = new[] {63,62,61];
How can I easily convert actualPositionsFound to a zero based sequence?
So if I had:
var actualPositionsFound = new[] {100,50,200];
I would like to end up with :
var result = new[] {1,0,2};
Update: In an attempt to make this clearer to avoid closing, what I believe is being asked for is to translate a list of numbers into another list of numbers representing the ascending order of the other list like a sort map, 0-based.
So { 16, 19, 2, 4 } would create a map { 2, 3, 0, 1 }, being 0-based.
If there are no duplicates:
var actualPositionsFound = new[] { 100, 50, 200 };
var indices = actualPositionsFound.OrderBy(n => n)
.Select((n, i) => new { n, i })
.ToDictionary(o => o.n, o => o.i);
var result = actualPositionsFound.Select(n => indices[n]).ToList();
Is it that you are looking for?
actualPositionsFound.Select((elem, idx) => new { elem, idx })
.OrderBy(wrap => wrap.elem)
.Select((wrap, idx) => new { wrap.idx, newIdx = idx })
.OrderBy(wrap => wrap.idx)
.Select(wrap => wrap.newIdx)
.ToArray();
actualPositionsFound
.OrderBy(x => x).ToList()
.Select(x => Array.IndexOf(actualPositionsFound,x)).ToArray();
This won't handle duplicates.
Is there a way that I could return duplicate values from an array in C#? also im looking to write a small algorithm that would return the most number of duplicate values in an array. for example
[1, 2,2,2 3,3] I need to return the duplicate values with the most number of occurrences and the number of occurrences as well.
I think I saw some post which said that It could be done using Linq but I have no clue what Linq is
Any help would be much appreciated.
Try this:
int[] data = new int[] { 1, 2, 2, 2, 3, 3 };
IGrouping<int, int> mostOccurrences = data
.GroupBy(value => value)
.OrderByDescending(group => group.Count())
.First();
Console.WriteLine("Value {0} occurred {1} time(s).", mostOccurrences.Key, mostOccurrences.Count());
Note that if multiple values occur the same number of times (such as if you added another 3 to that list), the above code will only list one of them. To handle that situation, try this:
int[] data = new int[] { 1, 2, 2, 2, 3, 3, 3 };
var occurrenceInfos = data
.GroupBy(value => value)
.Select(group =>
new {
Count = group.Count(),
Value = group.Key
}
);
int maxOccurrenceCount = occurrenceInfos.Max(info => info.Count);
IEnumerable<int> maxOccurrenceValues = occurrenceInfos
.Where(info => info.Count == maxOccurrenceCount)
.Select(info => info.Value);
foreach (int value in maxOccurrenceValues)
Console.WriteLine("Value {0} occurred {1} time(s).", value, maxOccurrenceCount);
Here's my take on this:
var data = new[] { 1, 2, 2, 2, 3, 3, };
var occurences =
data
.ToLookup(x => x)
.ToDictionary(x => x.Key, x => x.Count());
var mostOccurences =
occurences
.OrderByDescending(x => x.Value)
.First();
These will give you the following results: