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Extracting only the substring containing letters from a string containing digits strings and symbols

I have a string that is like the following:
string str = hello_16_0_2016;
What I want is to extract hello from the string. As in my program the string part can occur anywhere as it is autogenerated, so I cannot fix the position of my string.
For example: I can take the first five string from above and store it in a new variable.
But as occurring of letters is random and I want to extract only letters from the string above, so can someone guide me to the correct procedure to do this?

Could you just use a simple regular expression to pull out only alphabetic characters, assuming you only need a-z?
using System.Text.RegularExpressions;
var str = "hello_16_0_2016";
var onlyLetters = Regex.Replace(str, #"[^a-zA-Z]", "");
// onlyLetters = "hello"

I'd use something like this (uses Linq):
var str = "hello_16_0_2016";
var result = string.Concat(str.Where(char.IsLetter));
Check it out
Or, if performance is a concern (because you have to do this on a tight loop, or have to convert hundreds of thousands of strings), it'd probably be faster to do:
var result = new string(str.Where(char.IsLetter).ToArray());
Check it too

But as occurring of letters is random and I want to extract only
letters from the string above, so can someone guide me to the correct
procedure to do this?
The following will extract the first text, without numbers anywhere in the string:
Console.WriteLine( Regex.Match("hello_16_0_2016", #"[A-Za-z]+").Value ); // "hello"

How can I split a regex into exact words?

I need a little help regarding Regular Expressions in C#
I have the following string
"[[Sender.Name]]\r[[Sender.AdditionalInfo]]\r[[Sender.Street]]\r[[Sender.ZipCode]] [[Sender.Location]]\r[[Sender.Country]]\r"
The string could also contain spaces and theoretically any other characters. So I really need do match the [[words]].
What I need is a text array like this
"[[Sender.Name]]",
"[[Sender.AdditionalInfo]]",
"[[Sender.Street]]",
// ... And so on.
I'm pretty sure that this is perfectly doable with:
var stringArray = Regex.Split(line, #"\[\[+\]\]")
I'm just too stupid to find the correct Regex for the Regex.Split() call.
Anyone here that can tell me the correct Regular Expression to use in my case?
As you can tell I'm not that experienced with RegEx :)

Why dont you split according to "\r"?
and you dont need regex for that just use the standard string function
string[] delimiters = {#"\r"};
string[] split = line.Split(delimiters,StringSplitOptions.None);

Do matching if you want to get the [[..]] block.
Regex rgx = new Regex(#"\[\[.*?\]\]");
foreach (Match m in rgx.Matches(input))
Console.WriteLine(m.Groups[0].Value);
IDEONE

The regex you are using (\[\[+\]\]) will capture: literal [s 2 or more, then 2 literal ]s.
A regex solution is capturing all the non-[s inside doubled [ and ]s (and the string inside the brackets should not be empty, I guess?), and cast MatchCollection to a list or array (here is an example with a list):
var str = "[[Sender.Name]]\r[[Sender.AdditionalInfo]]\r[[Sender.Street]]\r[[Sender.ZipCode]] [[Sender.Location]]\r[[Sender.Country]]\r";
var rgx22 = new Regex(#"\[\[[^]]+?\]\]");
var res345 = rgx22.Matches(str).Cast<Match>().ToList();
Output:

Please tell me what the problem is c# regex.split()

string temp_constraint = row["Constraint_Name"].ToString();
string split_string = "FK_"+tableName+"_";
string[] words = Regex.Split(temp_constraint, split_string);
I am trying to split a string using another string.
temp_constraint = FK_ss_foo_ss_fee
split_string = FK_ss_foo_
but it returns a single dimension array with the same string as in temp_constraint
Please help

Your split operation works fine for me:
string temp_constraint = "FK_ss_foo_ss_fee";
string split_string = "FK_ss_foo_";
string[] words = Regex.Split(temp_constraint, split_string);
foreach (string word in words)
{
Console.WriteLine(">{0}<", word);
}
Output:
><
>ss_fee<
I think the problem is that your variables are not set to what you think they are. You will need to debug to find the error elsewhere in your program.
I would also avoid using Split for this (both Regex and String.Split). You aren't really splitting the input - you are removing a string from the start. Split might not always do what you want. Imagine if you have a foreign key like the following:
FK_ss_foo_ss_fee_FK_ss_foo_ss_bee
You want to get ss_fee_FK_ss_foo_ss_bee but split would give you ss_fee_ and ss_bee. This is a contrived example, but it does demonstrate that what you are doing is not a split.

You should use String.Split instead
string[] words =
temp_constraint.Split(new []{split_string}, StringSplitOptions.None);

string split uses a character array to split text and does the split by each character which is not often ideal.
The following article shows how to split text by an entire word
http://www.bytechaser.com/en/functions/ufgr7wkpwf/split-text-by-words-and-not-character-arrays.aspx

C# string manipulation

I have a string like
A150[ff;1];A160;A100;D10;B10'
in which I want to extract A150, D10, B10
In between these valid string, i can have any characters. The one part that is consistent is the semicolumn between each legitimate strings.
Again the junk character that I am trying to remove itself can contain the semi column

Without having more detail for the specific rules, it looks like you want to use String.Split(';') and then construct a regex to parse out the string you really need foreach string in your newly created collection. Since you said that the semi colon can appear in the "junk" it's irrelevant since it won't match your regex.

var input = "A150[ff+1];A160;A150[ff-1]";
var temp = new List<string>();
foreach (var s in input.Split(';'))
{
temp.Add(Regex.Replace(s, "(A[0-9]*)\\[*.*", "$1"));
}
foreach (var s1 in temp.Distinct())
{
Console.WriteLine(s1);
}
produces the output
A150
A160

First,you should use
string s="A150[ff;1];A160;A100;D10;B1";
s.IndexOf("A160");
Through this command you can get the index of A160 and other words.
And then s.Remove(index,count).

If you only want to remove the 'junk' inbetween the '[' and ']' characters you can use regex for that
Regex regex = new Regex(#"\[([^\}]+)\]");
string result = regex.Replace("A150[ff;1];A160;A100;D10;B10", "");
Then String.Split to get the individual items

How can I split a string using regex to return a list of values?

How can I take the string foo[]=1&foo[]=5&foo[]=2 and return a collection with the values 1,5,2 in that order. I am looking for an answer using regex in C#. Thanks

In C# you can use capturing groups
private void RegexTest()
{
String input = "foo[]=1&foo[]=5&foo[]=2";
String pattern = #"foo\[\]=(\d+)";
Regex regex = new Regex(pattern);
foreach (Match match in regex.Matches(input))
{
Console.Out.WriteLine(match.Groups[1]);
}
}

I don't know C#, but...
In java:
String[] nums = String.split(yourString, "&?foo[]");
The second argument in the String.split() method is a regex telling the method where to split the String.

I'd use this particular pattern:
string re = #"foo\[\]=(?<value>\d+)";
So something like (not tested):
Regex reValues = new Regex(re,RegexOptions.Compiled);
List<integer> values = new List<integer>();
foreach (Match m in reValues.Matches(...putInputStringHere...)
{
values.Add((int) m.Groups("value").Value);
}

Use the Regex.Split() method with an appropriate regex. This will split on parts of the string that match the regular expression and return the results as a string[].
Assuming you want all the values in your querystring without checking if they're numeric, (and without just matching on names like foo[]) you could use this: "&?[^&=]+="
string[] values = Regex.Split(“foo[]=1&foo[]=5&foo[]=2”, "&?[^&=]+=");
Incidentally, if you're playing with regular expressions the site http://gskinner.com/RegExr/ is fantastic (I'm just a fan).

Assuming you're dealing with numbers this pattern should match:
/=(\d+)&?/

This should do:
using System.Text.RegularExpressions;
Regex.Replace(s, !#"^[0-9]*$”, "");
Where s is your String where you want the numbers to be extracted.

Just make sure to escape the ampersand like so:
/=(\d+)\&/

Here's an alternative solution using the built-in string.Split function:
string x = "foo[]=1&foo[]=5&foo[]=2";
string[] separator = new string[2] { "foo[]=", "&" };
string[] vals = x.Split(separator, StringSplitOptions.RemoveEmptyEntries);