Can anyone help me with a nice LINQ expression for transforming a list of strings in another list containing only the shortest distinct common prefixes for the strings? The delimiter for prefixes is ..
Example: ["A", "A.B.D", "A", "A.B","E","F.E", "F","B.C"]
Goes to: ["A", "E", "F", "B.C"]
Removed:
"A.B.D" and "A.B" because the prefix "A" is already in the list
"A" because is duplicate
"F.E" because "F" already in list
Thanks!
Here you go:
from set in
(from item in list select item.Split('.')).GroupBy(x => x[0])
select
set.First()
.TakeWhile((part, index) => set.All(x => x.Length > index && x[index].Equals(part)))
.Aggregate((x, y) => String.Format("{0}.{1}", x, y));
By way of explanation:
First, we split all the strings by '.' and group by their first token.
Then, we look at the first element of each grouping, and we take parts from it while every element of that group continues to match (TakeWhile).
Then, we take all those parts and recompose them with the Aggregate(String.Format).
var items = new[] { "A", "A.B.D", "A", "A.B", "E", "F.E", "F", "B.C" };
var result = items
.OrderBy(s => s.Length)
.Distinct()
.ToLookup(s => s.Substring(0, 1))
.Select(g => g.First());
Order the items by their length, call distinct to remove duplicates, convert to groupings based on the first character, and select the first item in each group.
Yields:
"A", "E", "F", "B.C"
Edit: You probably don't even need Distinct as your selecting the first item in each group anyway, so it's really redundant.
EDIT: thanks to the comments for pointing out a bug in my earlier approach.
To get around that shortcoming this query should work:
var list = new List<string> { "A.B.D", "A", "A.B","E","F.E", "F","B.C", "B.C.D" };
var result = list.OrderBy(s => s)
.GroupBy(s => s[0])
.Select(g => g.First());
foreach (var s in result)
{
Console.WriteLine(s);
}
Incorrect approach:
The following query will group each string by the first character. Next, if the group count has more than one item the key is selected, otherwise the single item is selected.
var list = new List<string> { "A", "A.B.D", "A", "A.B", "E", "F.E", "F", "B.C" };
var result = list.GroupBy(s => s[0])
.Select(g => g.Count() > 1 ? g.Key.ToString() : g.Single());
foreach (var s in result)
{
Console.WriteLine(s);
}
Nailed it - assuming that if the source list contains "Q.X" & "Q.Y" then the result should contain "Q".
var source = new []
{
"A", "A.B.D", "A",
"A.B", "E", "F.E",
"F", "B.C",
"Q.X", "Q.Y",
"D.A.A", "D.A.B",
};
Func<string, int> startsWithCount =
s => source.Where(x => x.StartsWith(s)).Count();
var results =
(from x in source.Distinct()
let xx = x.Split('.')
let splits = Enumerable
.Range(1, xx.Length)
.Select(n => String.Join(".", xx.Take(n)))
let first = startsWithCount(splits.First())
select splits
.Where(s => startsWithCount(s) == first)
.Last()
).Distinct();
// results == ["A", "E", "F", "B.C", "Q", "D.A"]
string[] source = {"A", "A.B", "A.B.D", "B.C", "B.C.D", "B.D", "E", "F", "F.E"};
var result =
source.Distinct()
.Select(str => str.Split('.'))
.GroupBy(arr => arr[0])
.Select(g =>
{
return string.Join(".",
g.Aggregate((arr1, arr2) =>
{
return arr1.TakeWhile((str, index) => index < arr2.Length
&& str.Equals(arr2[index]))
.ToArray();
}));
});
Steps:
(1) Remove duplicated elements by Distinct()
(2) Split each element to an array, also get ready to be grouped
(3) Group those arrays by the first string in the array
(4) For each group, create one common prefix by aggregating all arrays in the group. The logic for aggregating is that for two arrays arr1 and arr2, take the elements in arr1 until (1)out of bounds (2) corresponding element in arr2 is different
Note: I add two return statements in the code, to make it look cleaner. It can be shorter if remove return and its {} brackets.
How about:
var possible = new List<string> { "A", "A.B.D", "A", "A.B", "E", "F.E", "F", "B.C" };
var shortest = possible.Distinct().Where(x => possible.Distinct().Where(y => !y.Equals(x) && x.StartsWith(y)).Count() == 0).ToList();
It checks the list against itself excluding items that are equal and any items that starts with any of the other items. I'm not sure about the effeciency though :)
I think it might be hard to solve with one single nice looking linq expression so I wrote a recursive function using linq that solves the problem:
class Program
{
static void Main(string[] args)
{
var input = new string[] { "A", "A.B.D", "A", "A.B", "E", "F.E", "F", "B.C", "B.C.D", "B.E" };
var output = FilterFunc(input);
foreach (var str in output)
Console.WriteLine(str);
Console.ReadLine();
}
static string[] FilterFunc(string[] input)
{
if (input.Length <= 1)
return input;
else
{
var firstElem = input[0];
var indexNr = firstElem.Length;
var maxFilteredElems = 0;
for (int i = firstElem.Length; i > 0; i--)
{
var numberOfFilteredElems = input.Where(x => x.StartsWith(firstElem.Substring(0, i))).Count();
if (numberOfFilteredElems > maxFilteredElems)
{
maxFilteredElems = numberOfFilteredElems;
indexNr = i;
}
}
var prefix = firstElem.Substring(0, indexNr);
var recursiveResult = FilterFunc(input.Where(x => !x.StartsWith(prefix)).ToArray());
var result = recursiveResult.ToList();
prefix = prefix.EndsWith(".") ? prefix.Substring(0, prefix.Length - 1) : prefix;
result.Insert(0, prefix);
return result.ToArray();
}
}
}
The code could probably be more effective and more organized but don't have time for that now. I think the other solutions are wrong so far, so that's why you get my longer one. I think you need to solve it recursively to be sure to get the shortest list.
My attempt, loop through items removing anything prefixed with another item.
static void Run()
{
var list = new string[] {"A", "A.B.D", "A",
"A.B", "E", "F.E",
"F", "B.C",
"Q.X", "Q.Y",
"D.A.A", "D.A.B"
};
int size = 0;
var prefixList = new string[list.Length];
Array.Copy(list, prefixList, list.Length);
for (int i = 0; i < list.Length; i++)
prefixList
= prefixList
.Where(c => !c.StartsWith(list[i]) || c == list[i])
.Distinct()
.ToArray();
foreach (string s in prefixList)
Console.WriteLine(s);
Console.ReadLine();
}
var list = new[] { "A.B.D", "A", "E", "A.B", "F", "F.E", "B.C.D", "B.C" };
var result = from s in list
group s by s.Split('.').First() into g
select LongestCommonPrefix(g);
foreach (var s in result)
{
Console.WriteLine(s);
}
Output:
A
E
F
B.C
Method to find longest common prefix from here (replace / with .).
My understanding of the question says a list containing both "B.C" and "B.E" but no "B" would get both "B.C" and "B.E".
string[] items = { "A", "A.B.D", "A", "A.B", "E", "F.E", "F", "B.C" };
char delimiter = '.';
var result = (from item in items.Distinct()
where !items.Any(other => item.StartsWith(other + delimiter))
select item).ToArray();
foreach (var item in result)
{
Console.WriteLine(item);
}
output
A
E
F
B.C
also works with multi-character prefixes
string[] items =
{
"Alpha",
"Alpha.Beta.Delta",
"Alpha",
"Alpha.Beta",
"Echo",
"Foxtrot.Echo",
"Foxtrot",
"Baker.Charlie"
};
gets
Alpha
Echo
Foxtrot
Baker.Charlie
If I strictly stick to the definition that dave provided, the answer is easier than it seems:
remove duplicates => distinct
remove any item that starts with any other item in the list
so we get:
from item in items.Distinct()
where !items.Any(other => other != item && item.StartsWith(other + '.'))
select item;
For the B.C and B.D question, this works as specified: Neither one includes the other, so none of the removing conditions mentioned by dave is triggered.
I admit that there might be more exciting anwers, but I'm afraid that's just not in the question ;)
Update: added delimiter to where clause in order to account for multi-char words. thanks svick!
var list = new List<string> { "A", "A.B.D", "A", "A.B", "E", "F.E", "F", "B.C" };
var result = (list.Select(a => a.Split('.').First())).Distinct();
Related
I am trying to make a dictionary that contains the index and matched elements of two sequences.
for example:-
List<string> A = new List<string> { "a", "b", "c", "d", "e", "f", "g" };
List<string> B = new List<string> { "a", "d", "e", "f" };
Now I want to build a dictionary that looks like this.
// Expected Output:-
// { "a" , 0 }
// { "d" , 3 }
// { "e" , 4 }
// { "f" , 5 }
where the first entry in dictionary is the common element in both the lists and second one is the index of that in the first list(A).
Not sure on how to phrase a Lambda Expression to do that.
Do to so, for each element in B use IndexOf in the A collection. Then use ToDictionary to convert it to the dictionary form you wanted
List<string> A = new List<string> { "a", "b", "c", "d", "e", "f", "g" };
List<string> B = new List<string> { "a", "d", "e", "f" };
var result = B.Select(item => new { item, Position = A.IndexOf(item) })
.ToDictionary(key => key.item, value => value.Position);
Keep in mind that the items in B must be unique for it to not fail on KeyAlreadyExists. In that case:
var result = B.Distinct()
.Select(item => new { item, Position = A.IndexOf(item) })
.ToDictionary(key => key.item, value => value.Position);
If you do not want results for items that weren't found:
var result = B.Distinct()
.Select(item => new { item, Position = A.IndexOf(item) })
.Where(item => item.Position != -1
.ToDictionary(key => key.item, value => value.Position);
This should do it:
List<string> A = new List<string>{"a","b","c","d","e","f","g"};
List<string> B = new List<string>{"a","d","e","f"};
var result = B.ToDictionary(k => k, v => A.IndexOf(b)});
try this:
List<string> A = new List<string> { "a", "b", "c", "d", "e", "f", "g" };
List<string> B = new List<string> { "a", "d", "e", "f" };
Dictionary<string, int> result = B.ToDictionary(x => x, x => A.IndexOf(x));
I am developing an asp.net application and I have the following list:
public static List<SelectedSongKey_List> SelectedSongKeys(int songId)
{
var db = new BMDWorshipEntities();
var results = (from x in db.Keys
where x.SongId == songId
select x.ChordKey).ToList();
var sortingOrder = new List<string>()
{
"Ab", "A", "Bb", "B", "C", "C#", "Db", "D", "Eb", "E", "F", "F#", "Gb", "G"
};
results = results.OrderBy(x => sortingOrder.IndexOf(x)).ToList();
var skList = new List<SelectedSongKey_List>();
foreach(var sk in results)
{
skList.Add(new SelectedSongKey_List()
{
SongKey = sk.Trim()
});
}
return skList;
}
This list will populate a drop-down list with all the existing ChordKeys:
Now I would like to make another List containing all the ChordKeys (Chords are in the sortingOrder) that don't exist on the db yet.
What results statement can I write in order to do that?
You can use the Except Clause
var exceptedList = sortingOrder.Except(results).ToList();
Start with the sortingOrder and keep only items not already in results.
var notInDb = sortingOrder.Where(item => !results.Contains(item));
You could use a lambda Where statement on sortingOrder to return only those values not contained in results:
var newChords = sortingOrder.Where(c => return !results.Contains(c));
EDIT: will leave this here for posterity, but Richa Garg's answer is easier to read.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Split List into Sublists with LINQ
I'm looking for some way to split an enumerable into three enumerables using LINQ, such that each successive item in the input is in the next sublist in in the sequence. So input
{"a", "b", "c", "d", "e", "f", "g", "h"}
would result in
{"a", "d", "g"}, {"b", "e", "h"}, {"c", "f"}
I've done it this way but I'm sure there must be a way to express this more elegantly using LINQ.
var input = new List<string> {"a", "b", "c", "d", "e", "f", "g", "h"};
var list = new List<string>[3];
for (int i = 0; i < list.Length; i++)
list[i] = new List<string>();
int column = 0;
foreach (string letter in input)
{
list[column++].Add(letter);
if (column > 2) column = 0;
}
This is what you are looking for:
(Splits by columns) Modified based on the previous posts
The key difference is in the group by, using mod instead of division.
Also I made it generic so it gives you back the proper type (as opposed to "object typed" code). You can just use type inference with generics.
public static IEnumerable<IEnumerable<T>> SplitColumn<T>( IEnumerable<T> source ) {
return source
.Select( ( x, i ) => new { Index = i, Value = x } )
.GroupBy( x => x.Index % 3 )
.Select( x => x.Select( v => v.Value ).ToList() )
.ToList();
}
How to use linq to select something fit the conditions below,
I want select the words JUST contains the string in ArStr[], i.e. a,b,c
In the Wordslist, "aabb" don't contain "c", "aacc" don't contain "b", "aabbccd" contain "d".
So they are not the words I want.
Please help.
Wordslist :
aabb
aacc
aaabbcc
aabbbcc
aabbccd
ArStr[] :
"a"
"b"
"c"
Expected Query:
aaabbcc
aabbbcc
IEnumerable<Word> Query =
from Word in Wordslist
where
Word.Value.Contains(ArStr[0]) // 1
&& Word.Value.Contains(ArStr[1]) // 2
&& Word.Value.Contains(ArStr[2]) // 3
select Word;
You can construct a set of white-list characters and then filter those words that are set-equal with that white-list (ignoring duplicates and order).
var chars = new HashSet<char>(ArStr); // Construct white-list set
var query = from word in wordsList
where chars.SetEquals(word) // Word must be set-equal with white-list
select word;
or
var query = wordsList.Where(chars.SetEquals);
As you've probably noticed, the query you've written does return "aabbccd", because that string contain "a", it contains "b", and it contains "c".
Assuming that ArStr can only contain one-character strings, and you want to return strings that contain only the specified characters, so you should say (adapted from Ani's answer):
var chars = new HashSet<char>(ArStr.Select(s => s[0]));
var query = wordslist.Where(w => chars.SetEquals(w.Value));
However, if the ArStr elements could be more than one character long, the problem needs to be better defined, and the solution will be more complicated.
Use this method to evaluate a word if it passes your condition or not:
bool HasValidCharacters(string word)
{
var allowedCharacters = new List<string> { "a", "b", "c" };
return string.Join("", word.GroupBy(c => c)
.Select(g => g.Key)
.OrderBy(g => g))
.Equals(string.Join("", allowedCharacters.OrderBy(c => c)));
}
Then simply call the method to get the required list:
var words = new List<string> { "aabb", "aacc", "aaabbcc", "aabbbcc", "aabbccd" };
var matchingWords = words.Where(HasValidCharacters);
You could try this:
List<String> words = new List<string> { "aabb", "aacc", "aaabbcc", "aabbbcc", "aabbccd" };
List<string> allowed = new List<string> { "a", "b", "c" };
var lst = words.Where(word => allowed.All(a => word.Contains(a) && !Regex.IsMatch(word, "[^" + string.Join("", allowed) + "]"))).ToList();
Just another way to implement it.
I think you can use String.Trim Method (Char()) on each element , then the empty element is you want .
var arr = new string[] { "aabb", "aacc", "aaabbcc", "aabbbcc", "aabbccd" };
var arStr = new string[] { "a", "b", "c" };
var str = string.Join("", arStr);
var result = from p in arr
let arCharL = arStr.Select(a => Convert.ToChar(a)).ToArray()
let arCharR = p.ToCharArray()
where p.Trim(arCharL).Length == 0 && str.Trim(arCharR).Length == 0
select p;
Dear all , this is something like my previous question How to get moving combination from two List<String> in C#?
I'm having a masterlist and two childlist like below
List<String> MasterList = new List<string> { "A", "B", "C", "D", "E" };
List<String> ListOne = new List<string> { "A", "B", "C" };
List<String> ListTwo = new List<String> { "B", "D" };
I just need to get the running combination from the above list for that i'm using like(previous question's answer(Thanks Danny Chen))
List<String> Result = new List<string>();
Result = ListOne.SelectMany((a, indexA) => ListTwo
.Where((b, indexB) => ListTwo
.Contains(a) ? !b.Equals(a) && indexB > indexA :
!b.Equals(a)).Select(b => string.Format("{0}-{1}", a, b))).ToList();
so the Result list will contain
"A-B"
"A-D"
"B-D"
"C-B"
"C-D"
Now my problem is the sorting issue
In the above result the fourth entry is C-B but it should be B-C. Because in the MasterList the C is after B.
How to do this in my existing linq .
Please help me to do this.
Not really clear on the exact requirement here, so does the MasterList dictate which of the two items should appear first? What about the order of the X1-X2 list? i.e. should B-C appear before B-D because C appears before D in the MasterList?
Anyway, here's something that produces the result you've asked for so far:
List<String> MasterList = new List<string> { "A", "B", "C", "D", "E" };
List<String> ListOne = new List<string> { "A", "B", "C" };
List<String> ListTwo = new List<String> { "B", "D" };
ListOne.SelectMany(i =>
ListTwo.Where(i2 => i != i2)
.Select(i2 =>
{
if (MasterList.IndexOf(i) < MasterList.IndexOf(i2))
return string.Format("{0}-{1}", i, i2);
else
return string.Format("{0}-{1}", i2, i);
}
));
outputs:
A-B
A-D
B-D
B-C
C-D