Develop Reference

C# RegEx Pattern to Split a String into 2 Character Substring

I am trying to figure out a regex to use to split a string into 2 character substring.
Let's say we have the following string:
string str = "Idno1";
string pattern = #"\w{2}";
Using the pattern above will get me "Id" and "no", but it will skip the "1" since it doesn't match the pattern. I would like the following results:
string str = "Idno1"; // ==> "Id" "no" "1 "
string str2 = "Id n o 2"; // ==> "Id", " n", " o", " 2"

Linq can make easy the code. Fiddle version works
The idea: I have a chunkSize = 2 as your requirement, then, Take the string at the index (2,4,6,8,...) to get the chunk of chars and Join them to string.
public static IEnumerable<string> ProperFormat(string s)
{
var chunkSize = 2;
return s.Where((x,i) => i % chunkSize == 0)
.Select((x,i) => s.Skip(i * chunkSize).Take(chunkSize))
.Select(x=> string.Join("", x));
}
With the input, I have the output
Idno1 -->
Id
no
1
Id n o 2 -->
Id
n
o
2

Linq is really better in this case. You can use this method - it will allow to split string in chunks of arbitrary size:
public static IEnumerable<string> SplitInChunks(string s, int size = 2)
{
return s.Select((c, i) => new {c, id = i / size})
.GroupBy(x => x.id, x => x.c)
.Select(g => new string(g.ToArray()));
}
But if you are bound to regex, use this code:
public static IEnumerable<string> SplitInChunksWithRegex(string s, int size = 2)
{
var regex = new Regex($".{{1,{size}}}");
return regex.Matches(s).Cast<Match>().Select(m => m.Value);
}

c# ordering strings with different formats

I have Licence plate numbers which I return to UI and I want them ordered in asc order:
So let's say the input is as below:
1/12/13/2
1/12/11/3
1/12/12/2
1/12/12/1
My expected output is:
1/12/11/3
1/12/12/1
1/12/12/2
1/12/13/2
My current code which is working to do this is:
var orderedData = allLicenceNumbers
.OrderBy(x => x.LicenceNumber.Length)
.ThenBy(x => x.LicenceNumber)
.ToList();
However for another input sample as below:
4/032/004/2
4/032/004/9
4/032/004/3/A
4/032/004/3/B
4/032/004/11
I am getting the data returned as:
4/032/004/2
4/032/004/9
4/032/004/11
4/032/004/3/A
4/032/004/3/B
when what I need is:
4/032/004/2
4/032/004/3/A
4/032/004/3/B
4/032/004/9
4/032/004/11
Is there a better way I can order this simply to give correct result in both sample inputs or will I need to write a custom sort?
EDIT
It wont always be the same element on the string.
This could be example input:
2/3/5/1/A
1/4/6/7
1/3/8/9/B
1/3/8/9/A
1/5/6/7
Expected output would be:
1/3/8/9/A
1/3/8/9/B
1/4/6/7
1/5/6/7
2/3/5/1/A

You should split your numbers and compare each part with each other. Compare numbers by value and strings lexicographically.
var licenceNumbers = new[]
{
"4/032/004/2",
"4/032/004/9",
"4/032/004/3",
"4/032/004/3/A",
"4/032/004/3/B",
"4/032/004/11"
};
var ordered = licenceNumbers
.Select(n => n.Split(new[] { '/' }))
.OrderBy(t => t, new LicenceNumberComparer())
.Select(t => String.Join("/", t));
Using the following comparer:
public class LicenceNumberComparer: IComparer<string[]>
{
public int Compare(string[] a, string[] b)
{
var len = Math.Min(a.Length, b.Length);
for(var i = 0; i < len; i++)
{
var aIsNum = int.TryParse(a[i], out int aNum);
var bIsNum = int.TryParse(b[i], out int bNum);
if (aIsNum && bIsNum)
{
if (aNum != bNum)
{
return aNum - bNum;
}
}
else
{
var strCompare = String.Compare(a[i], b[i]);
if (strCompare != 0)
{
return strCompare;
}
}
}
return a.Length - b.Length;
}
}

If we can assume that
Number plate constist of several (one or more) parts separated by '/', e.g. 4, 032, 004, 2
Each part is not longer than some constant value (3 in the code below)
Each part consist of either digits (e.g. 4, 032) or non-digits (e.g. A, B)
We can just PadLeft each number plate's digit part with 0 in order to compare not "3" and "11" (and get "3" > "11") but padded "003" < "011":
var source = new string[] {
"4/032/004/2",
"4/032/004/9",
"4/032/004/3/A",
"4/032/004/3/B",
"4/032/004/11",
};
var ordered = source
.OrderBy(item => string.Concat(item
.Split('/') // for each part
.Select(part => part.All(char.IsDigit) // we either
? part.PadLeft(3, '0') // Pad digit parts e.g. 3 -> 003, 11 -> 011
: part))); // ..or leave it as is
Console.WriteLine(string.Join(Environment.NewLine, ordered));
Outcome:
4/032/004/2
4/032/004/3/A
4/032/004/3/B
4/032/004/9
4/032/004/11

You seem to be wanting to sort on the fourth element of the string (delimited by /) in numeric rather than string mode.. ?
You can make a lambda more involved/multi-statement by putting it like any other method code block, in { }
var orderedData = allLicenceNumbers
.OrderBy(x =>
{
var t = x.Split('/');
if(t.Length<4)
return -1;
else{
int o = -1;
int.TryParse(t[3], out o);
return o;
}
)
.ToList();
If you're after sorting on more elements of the string, you might want to look at some alternative logic, perhaps if the first part of the string will always be in the form N/NNN/NNN/??/?, then do:
var orderedData = allLicenceNumbers
.OrderBy(w => w.Remove(9)) //the first 9 are always in the form N/NNN/NNN
.ThenBy(x => //then there's maybe a number that should be parsed
{
var t = x.Split('/');
if(t.Length<4)
return -1;
else{
int o = -1;
int.TryParse(t[3], out o);
return o;
}
)
.ThenBy(y => y.Substring(y.LastIndexOf('/'))) //then there's maybe A or B..
.ToList();
Ultimately, it seems that more and more outliers will be thrown into the mix, so you're just going to have to keep inventing rules to sort with..
Either that or change your strings to standardize everything (int an NNN/NNN/NNN/NNN/NNA format for example), and then sort as strings..
var orderedData = allLicenceNumbers
.OrderBy(x =>
{
var t = x.Split('/');
for(int i = 0; i < t.Length; i++) //make all elements in the form NNN
{
t[i] = "000" + t[i];
t[i] = t[i].Substring(t[i].Length - 3);
}
return string.Join(t, "/");
}
)
.ToList();
Mmm.. nasty!

create dictionary occurrences for each letter c#

We have a program that shows you how many times a letter is repeated in a text
string txt = input.text.ToLower();
txt = Regex.Replace(txt, #"\s+", "").Replace(")","").Replace("(","").Replace(".","").Replace(",","").Replace("!","").Replace("?","") ;
var letterCount = txt.Where(char.IsLetter).GroupBy(c => c).Select(v => new { Letter = v.Key, count = v.Count() });
foreach (var c in letterCount)
{
Debug.Log(string.Format("Caracterul:{0} apare {1} ori", c.Letter.ToString(), c.count));
}
And how do I give for the most repeating letter the value of 26, then for the one that repeats the less it gets 25 and for the one that only once a value in alphabetical order?
For example, the text "we are all happy"
Letter A is repeated three times and has the value of 26
For letter L 25
For P 24 and others in alphabetical order
And, finally, get their sum?
Sorry for my English!!!

You can use this LINQ approach:
string input = "we are all happy";
var allCharValues = input.ToLookup(c => c)
.Where(g => g.Key != ' ') // or you want spaces?
.OrderByDescending(g => g.Count())
.ThenBy(g => g.Key) // you mentioned alphabetical ordering if two have same count
.Select((x, index) => new { Char = x.Key, Value = 26 - index, Count = x.Count() });
foreach (var x in allCharValues)
Console.WriteLine($"Char:{x.Char} Value:{x.Value} Count:{x.Count}");
int sum = allCharValues.Select(x => x.Value).Sum();

In relation to your question about removing unwanted characters:
I think you'd be better of just keeping all characters between a and z. You could write an extension method to do this, and convert to lowercase at the same time:
public static class StringExt
{
public static string AlphabeticChars(this string self)
{
var alphabeticChars = self.Select(char.ToLower).Where(c => 'a' <= c && c <= 'z');
return new string(alphabeticChars.ToArray());
}
}
Then you can use an approach as follows. This is similar to Tim's approach, but this uses GroupBy() to count the occurrences; it also uses the new Tuple syntax from C#7 to simplify things. Note that this ALSO names the tuple properties, so they are not using the default Item1 and Item2.
string txt = "we, (are?) all! happy.";
var r = txt
.AlphabeticChars()
.GroupBy(c => c)
.Select(g => (Count: g.Count(), Char: g.Key))
.OrderByDescending(x => x.Count)
.ThenBy(x => x.Char)
.Select((v, i) => (Occurance: v, Index: 26-i));
int sum = r.Sum(c => c.Occurance.Count * c.Index);
Console.WriteLine(sum);

How to find maximum number of repeated string in a string in a list of string in c#

If we have a list of strings, then how we can find the list of strings that have the maximum number of repeated symbol by using LINQ.
List <string> mylist=new List <string>();
mylist.Add("%1");
mylist.Add("%136%250%3"); //s0
mylist.Add("%1%5%20%1%10%50%8%3"); // s1
mylist.Add("%4%255%20%1%14%50%8%4"); // s2
string symbol="%";
List <string> List_has_MAX_num_of_symbol= mylist.OrderByDescending(s => s.Length ==max_num_of(symbol)).ToList();
//the result should be a list of s1 + s2 since they have **8** repeated '%'
I tried
var longest = mylist.Where(s => s.Length == mylist.Max(m => m.Length)) ;
this gives me only one string not both

Here's a very simple solution, but not exactly efficient. Every element has the Count operation performed twice...
List<string> mylist = new List<string>();
mylist.Add("%1");
mylist.Add("%136%250%3"); //s0
mylist.Add("%1%5%20%1%10%50%8%3"); // s1
mylist.Add("%4%255%20%1%14%50%8%4"); // s2
char symbol = '%';
var maxRepeat = mylist.Max(item => item.Count(c => c == symbol));
var longest = mylist.Where(item => item.Count(c => c == symbol) == maxRepeat);
It will return 2 strings:
"%1%5%20%1%10%50%8%3"
"%4%255%20%1%14%50%8%4"

Here is an implementation that depends upon SortedDictionary<,> to get what you're after.
var mylist = new List<string> {"%1", "%136%250%3", "%1%5%20%1%10%50%8%3", "%4%255%20%1%14%50%8%4"};
var mappedValues = new SortedDictionary<int, IList<string>>();
mylist.ForEach(str =>
{
var count = str.Count(c => c == '%');
if (mappedValues.ContainsKey(count))
{
mappedValues[count].Add(str);
}
else
{
mappedValues[count] = new List<string> { str };
}
});
// output to validate output
foreach (var str in mappedValues.Last().Value)
{
Console.WriteLine(str);
}
Here's one using LINQ that gets the result you're after.
var result = (from str in mylist
group str by str.Count(c => c == '%')
into g
let max = (from gKey in g select g.Key).Max()
select new
{
Count = max,
List = (from str2 in g select str2)
}).LastOrDefault();

OK, here's my answer:
char symbol = '%';
var recs = mylist.Select(s => new { Str = s, Count = s.Count(c => c == symbol) });
var maxCount = recs.Max(x => x.Count);
var longest = recs.Where(x => x.Count == maxCount).Select(x => x.Str).ToList();
It is complicated because it has three lines (the char symbol = '%'; line excluded), but it counts each string only once. EZI's answer has only two lines, but it is complicated because it counts each string twice. If you really want a one-liner, here it is:
var longest = mylist.Where(x => x.Count(c => c == symbol) == mylist.Max(y => y.Count(c => c == symbol))).ToList();
but it counts each string many times. You can choose whatever complexity you want.

We can't assume that the % is always going to be the most repeated character in your list. First, we have to determine what character appears the most in an individual string for each string.
Once we have the character and it maximum occurrence, we can apply Linq to the List<string> and grab the strings that contain the character equal to its max occurrence.
using System;
using System.Collections.Generic;
using System.Linq;
public class Program
{
public static void Main()
{
List <string> mylist=new List <string>();
mylist.Add("%1");
mylist.Add("%136%250%3");
mylist.Add("%1%5%20%1%10%50%8%3");
mylist.Add("%4%255%20%1%14%50%8%4");
// Determine what character appears most in a single string in the list
char maxCharacter = ' ';
int maxCount = 0;
foreach (string item in mylist)
{
// Get the max occurrence of each character
int max = item.Max(m => item.Count(c => c == m));
if (max > maxCount)
{
maxCount = max;
// Store the character whose occurrence equals the max
maxCharacter = item.Select(c => c).Where(c => item.Count(i => i == c) == max).First();
}
}
// Print the strings containing the max character
mylist.Where(item => item.Count(c => c == maxCharacter) == maxCount)
.ToList().ForEach(Console.WriteLine);
}
}
Results:
%1%5%20%1%10%50%8%3
%4%255%20%1%14%50%8%4
Fiddle Demo

var newList = myList.maxBy(x=>x.Count(y=>y.Equals('%'))).ToList();
This should work. Please correct syntax if wrong anywhere and update here too if it works for you.

Mapping numbers to letters

I had an interview question asking this:
text file has following lines>
1: A C D
4: A B
5: D F
7: A E
9: B C
*Every line has a unique integer followed by a colon and one or
more letters. These letters are
delimited spaces (one or more)>
#2 Write a short program in the language
of your choice that outputs a sorted
list like
A: 1 4 7
B: 4 9
C: 1 9
D: 1 5
E: 7
F: 5
I'm not looking for someone to solve it, but I always get confused with problems like this. I'd like to do it in C# and was wondering should I store each line in a 2d array? What is the best way to handle this. After storing it how do I relist each line with letters rather then numbers?
Just looking for pointers here.

You can solve the problem by creating a Lookup mapping letters to a collection of numbers. You can use the extension method ToLookup to create a Lookup.
Warning: Spoilers ahead
Using LINQ you can do it like this (breaks on invalid input):
var text = #"1: A C D
4: A B
5: D F
7: A E
9: B C";
var lookup = text
.Split(new[] { '\r', '\n' }, StringSplitOptions.RemoveEmptyEntries)
.Select(
line => new {
Number = Int32.Parse(line.Split(':').First()),
Letters = line.Split(':').Skip(1).First().Split(
new[] {' '}, StringSplitOptions.RemoveEmptyEntries
)
}
)
.SelectMany(x => x.Letters, (x, letter) => new { x.Number, Letter = letter })
.OrderBy(x => x.Letter)
.ToLookup(x => x.Letter, x => x.Number);
foreach (var item in lookup)
Console.WriteLine(item.Key + ": " + String.Join(" ", item.ToArray()));

In case you are familiar with LINQ the below code can give you what you are looking for:
var result = File.ReadAllLines("inFile").SelectMany(line =>
{
var ar = line.Split(" ".ToCharArray());
var num = int.Parse(ar[0].Split(":".ToCharArray())[0]);
return ar.Skip(1).Select(s => new Tuple<string, int>(s, num));
}).GroupBy(t => t.Item1).OrderByDescending(g => g.Count())
.Select(g => g.Key + ": " + g.Select(t => t.Item2.ToString()).Aggregate( (a,b) => a + " " + b));
File.WriteAllLines("outFile", result);

I know you said you didn't want full answers, but this kind of thing is fun. It looks like others have come up with similar solutions, but here's another way to represent it - in "one line" of code (but lots of brackets!) :)
var data = #"1: A C D
4: A B
5: D F
7: A E
9: B C";
Console.WriteLine(
String.Join(
Environment.NewLine,
(from line in data.Split(new[] { '\r', '\n' }, StringSplitOptions.RemoveEmptyEntries)
let lineParts = line.Split(new[] { ':', ' ' }, StringSplitOptions.RemoveEmptyEntries)
from letter in lineParts.Skip(1)
select new { Number = lineParts[0], Letter = letter })
.ToLookup(l => l.Letter, l => l.Number)
.OrderBy(l => l.Key)
.Select(l => String.Format("{0}: {1}", l.Key, String.Join(" ", l)))));
Oh, and would I write code like that in production? Probably not, but it's fun in an exercise like this!

The thing that will help you solve this
IDictionary<char, IList<int> >
Yet Another Linq Masturbatory Implementation ("Look Ma! No loops!")
using System;
using System.IO;
using System.Linq;
public static class Program
{
public static void Main(string[] args)
{
File.ReadAllLines("input.txt")
.Select(line =>
{
var split = line.Split(":".ToCharArray(), 2);
return new { digit = split[0].Trim().Substring(0,1),
chars = split[1]
.Split(" \t".ToCharArray())
.Select(s=>s.Trim())
.Where(s => !String.IsNullOrEmpty(s))
.Select(s => s[0])
};
})
.SelectMany(p => p.chars.Select(ch => new { p.digit, ch }))
.GroupBy(p => p.ch, p => p.digit)
.ToList()
.ForEach(g => Console.WriteLine("{0}: {1}", g.Key, string.Join(" ", g)));
}
}
Of course you can replace GroupBy with ToLookup

I will use a Dictionary<string,List<int>> I will read the input and add 1 into the list at keys A,C,D, A at keys A,B etc, so having the result is just a lookup by letter.
So like this, in a non esoteric way:
string inp = #"1: A C D
4: A B
5: D F
7: A E
9: B C";
Dictionary<string, List<int>> res = new Dictionary<string, List<int>>();
StringReader sr = new StringReader(inp);
string line;
while (null != (line = sr.ReadLine()))
{
if (!string.IsNullOrEmpty(line))
{
string[] tokens = line.Split(": ".ToArray(),StringSplitOptions.RemoveEmptyEntries);
int idx = int.Parse(tokens[0]);
for (int i = 1; i < tokens.Length; ++i)
{
if (!res.ContainsKey(tokens[i]))
res[tokens[i]] = new List<int>();
res[tokens[i]].Add(int.Parse(tokens[0]));
}
}
}
res will contain the result of letter->list of numbers.

String parsing using Split(":") and Split(" ").
Then fill
Dictionary<int, List<string>>
and translate it into
Dictionary<string, List<int>>

You could store the input in an IDictionary, and reverse it to produce your output.
Take a look at this question.

I see that multiple similar (loops) and not so similar (linq) solutions were already posted but since i've written this i thought i'd throw it in the mix.
static void Main(string[] args)
{
var result = new SortedDictionary<char, List<int>>();
var lines = System.IO.File.ReadAllLines(#"input.txt");
foreach (var line in lines)
{
var split = line.Split(new[] {' '}, StringSplitOptions.RemoveEmptyEntries);
var lineNumber = Int32.Parse(split[0].Substring(0,1));
foreach (var letter in split.Skip(1))
{
var key = letter[0];
if (!result.ContainsKey(key))
{
result.Add(key, new List<int> { lineNumber });
}
else
{
result[key].Add(lineNumber);
}
}
}
foreach (var item in result)
{
Console.WriteLine(String.Format("{0}: {1}", item.Key, String.Join(" ", item.Value)));
}
Console.ReadKey();
}

An important part of the interview process is asking about and verifying assumptions. Although your description states the file is structured as an integer followed by letters, the example you give shows the integers in increasing order. If that's the case, you can avoid all of the LINQ craziness and implement a much more efficient solution:
var results = new Dictionary<char, List<int>>();
foreach (var line in File.ReadAllLines(#"input.txt"))
{
var split = line.Split(new []{' '}, StringSplitOptions.RemoveEmptyEntries);
var num = int.Parse(split[0].TrimEnd(':'));
for (int i = 1; i < split.Length; i++)
{
char letter = split[i][0];
if (!results.ContainsKey(letter))
results[letter] = new List<int>();
results[letter].Add(num);
}
}