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How can I find a certain letter in a String in C#?

How can I search a certain letter (char) in a String?
I have to code a little riddle. You basicalley have to guess the right letters of an unknown word. Only the first letter is shown.
Example: "Apple"
A____ --> that's what you actually see. Now, the player has to input a letter/char and if it is inculded in the String "Apple", the correct letter will be added.
Example: input = e
A___e
Thx.

You can use String.IndexOf.
Example:
var str = "Apple";
var c = 'p';
var i = str.IndexOf(c);
// i will be the index of the first occurrence of 'p' in str, or -1 if not found.
if (i == -1)
{
// not found
}
else
{
do
{
// do something with index i, which is != -1
i = str.IndexOf(c, i + 1);
} while (i != -1);
}

If you want to find all letter indices, you can try this LINQ solution:
var str = "Apple";
var letter = 'p';
var charIndexMap = str
.Select((ch, idx) => (ch, idx))
.GroupBy(pair => pair.ch)
.ToDictionary(entry => entry.Key,
entry => entry.Select(pair => pair.idx));
if (charIndexMap.TryGetValue(letter, out var value))
{
Console.WriteLine("[" + string.Join(", ", value) + "]");
} else
{
// not found
}
Output:
[1, 2]
Explanation:
Use Enumerable.Select to map over the characters and indices and convert them to (character, index) tuples.
Use Enumerable.GroupBy to group tuples by character.
Convert grouped results to a dictionary using Enumerable.ToDictionary, which maps each character to an IEnumerable<int> of indices.
Use Dictionary<TKey,TValue>.TryGetValue(TKey, TValue) to get the associated indices for the letter.

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);
}

Retrieving Numeric value before a decimal in a string value

I am working on a routine in C#
I have a list of alphanumeric sheet numbers that I would like to retrieve the numbers before the decimal to use in my routine.
FP10.01-->10
M1.01-->1
PP8.01-->8
If possible, how can something like this be achieved as either a string or integer?

You could use a regex:
Regex r = new Regex("([0-9]+)[.]");
string s = "FP10.01";
var result = Convert.ToInt32(r.Match(s).Groups[1].ToString()); //10

string input = "FP10.01";
string[] _input = input.Split('.');
string num = find(_input[0]);
public string find(string input)
{
char[] _input = input.ToArray();
int number;
string result = null;
foreach (var item in _input)
{
if (int.TryParse(item.ToString(), out number) == true)
{
result = result + number;
}
}
return result;
}

To accumulate the resulting elements into a list, you can do something like:
List<string> myList = new List<string>(){ "FP10.01","M1.01", "PP8.01"};
List<int> resultSet =
myList.Select(e =>
Regex.Replace(e.Substring(0, e.IndexOf('.')), #"[^\d]", string.Empty))
.Select(int.Parse)
.ToList();
This will take each element in myList and in turn, take a substring of each element from index 0 until before the . and then replace all the non-numeric data with string.Empty and then finally parse the string element into an int and store it into a list.
another variant would be:
List<int> resultSet =
myList.Select(e => e.Substring(0, e.IndexOf('.')))
.Select(e => string.Join(string.Empty, e.Where(char.IsDigit)))
.Select(int.Parse)
.ToList();
or if you want the elements to be strings then you could do:
List<string> resultSet =
myList.Select(e => e.Substring(0, e.IndexOf('.')))
.Select(e => string.Join(string.Empty, e.Where(char.IsDigit)))
.ToList();
To retrieve a single element of type string then you can create a helper function as such:
public static string GetValueBeforeDot(string input){
return input.Substring(0, input.IndexOf('.'))
.Where(char.IsDigit)
.Aggregate(string.Empty, (e, a) => e + a);
}
To retrieve a single element of type int then the helper function should be:
public static int GetValueBeforeDot(string input){
return int.Parse(input.Substring(0, input.IndexOf('.'))
.Where(char.IsDigit)
.Aggregate(string.Empty, (e, a) => e + a));
}

This approach removes alphabet characters by replacing them with an empty string. Splitting on the '.' character will leave you with a two element array consisting of numbers at index 0 and after decimal values at index 1.
string input = "FP10.01";
var result = Regex.Replace(input, #"([A-Za-z]+)", string.Empty).Split('.');
var beforeDecimalNumbers = result[0]; // 10
var afterDecimalNumbers = result[1]; // 01

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.

Linq Query to match string values in an xml

I have a XML document which looks like
<recipes>
<ingredient value"1">APPLE</ingredient>
<ingredient value"2">BANANA</ingredient>
<ingredient value"3">APPLE ORANGE</ingredient>
<ingredient value"4">APPLE BANANA</ingredient>
<ingredient value"5">APPLE STRAWBERRY</ingredient>
<ingredient value"6">GRAPES</ingredient>
</recipes>
Now the user inputs some string eg Apple Grapes Banana. I sort it alphabetically and try to match it with one of the values by recursively eliminating the last word using string manipulation. But I am sure there is a more efficient way to do this in Linq. I want the query to return the closest match in XML <ingredient value"4">APPLE BANANA</ingredient>.
string str = "APPLE BANANA GRAPES"; // user input arranged by ascending alphabet and capitalized
XDocument xdoc = XDocument.Load(above xml);// gets above xml
var h = xdoc.Root.Elements("ingredient").FirstOrDefault(u => u.Value == str);//recurse these steps
if (h == null)
{
str = str.Remove(str.LastIndexOf(" "));//recurse these steps
}
//check if str matches any value;
//if not remove last word from str and check again;

I would try something like this :
string str = "APPLE BANANA GRAPES";
String[] criterias = str.Split(' ');
XDocument x = XDocument.Parse(yourXmlString);
var result =
x.Root.Elements()
// count # of matches for each element
.Select(e => new {e, num = criterias.Count(c => e.Value.Contains(c))})
// order by # of matches, then alphabetically
.OrderByDescending(r => r.num).ThenBy(r => r.e.Value)
// get a combination e: XElement, num: # of matches
.FirstOrDefault();
Edit : Not sure if the matching should be a prefix of the search string. Maybe it is more something like this :
var result =
x.Root.Elements()
// get prefixes
.Where(e => str.StartsWith(e.Value))
// count matchings
.Select(e=>new {e, num=e.Value.Split(' ').Length})
// get max matchings
.OrderByDescending(r => r.num).ThenBy(r => r.e.Value)
.FirstOrDefault();

You would need multiple conditins for closest match here.
For instance
var h = xdoc.Root.Elements("ingredient").FirstOrDefault(u => str.Contains(u.value))
is a condition that would return a nearer value in the example.

I have a simple recursive to present
public string FindValueFromText(XDocument xdoc, string str)
{
while (str != "")
{
var h = xdoc.Root.Elements("ingredient").FirstOrDefault(u => u.Value == str);
if (h == null)
{
str = str.Remove(str.LastIndexOf(" "));
FindValueFromText(xdoc, str); //recursive
}
else
{
return h.Attribute("value").Value;
}
}
return "Not found value";
}
Add these lines where you want to call above method
XDocument xDoc = XDocument.Load(xmlFilePath);
string value = FindValueFromText(xDoc, "APPLE BANANA GRAPES");