We Keep Coding

validating multiple occurence of e-mails in string in most efficient way

I have string coming in this format as shown bellow:
"mark345345#test.com;rtereter#something.com;terst#gmail.com;fault#mail"
What would be the most efficient way to validate each of these above and fail if it is not valid e-mail?

you can use EmailAddressAttribute class of System.ComponentModel.DataAnnotations namespace for validating the email address. Before that you need to split up individual mails and check whether it is valid or not. the following code will help you to collect the valid mails and invalid mails seperately.
List<string> inputMails = "mark345345#test.com;rtereter#something.com;terst#gmail.com;fault#mail".Split(';').ToList();
List<string> validMails = new List<string>();
List<string> inValidMails = new List<string>();
var validator = new EmailAddressAttribute();
foreach (var mail in inputMails)
{
if (validator.IsValid(mail))
{
validMails.Add(mail);
}
else
{
inValidMails.Add(mail);
}
}

You can use Regex or you might split the string by ';' and try to create a System.Net.Mail.MailAddress instance for each and every address. FormatException will occur if address is not in a recognized format.

If you're sure, that all e-mails are semi colon separated, you can split it and make a list of all. The best way for me to validate each e-mail is to use a regex pattern. I've used this one:
var emailPattern = #"(?=^.{1,64}#)^[a-zA-Z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-zA-Z0-9!#$%&'*+/=?^_`{|}~-]+)*#(?=.{1,255}$|.{1,255};)(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?\.)+[a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])(;(?=.{1,64}#)[a-zA-Z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-zA-Z0-9!#$%&'*+/=?^_`{|}~-]+)*#(?=.{1,255}$|.{1,255};)(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?\.)+[a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9]))*$";
var incomingString = "mark345345#test.com;rtereter#something.com;terst#gmail.com;fault#mail";
var emails = incomingString.Split(';').ToList();
foreach (var email in emails)
{
if (new Regex(emailPattern).IsMatch(email))
{
// your logic here
}
}

Since .Net has out of the box ways to validate an email id, I would not use a regex and rely upon .Net. e.g the EmailAddressAttribute from System.ComponentModel.DataAnnotations.
A clean way to use it would be something like:
var emailAddressAttribute = new EmailAddressAttribute();
var groups = yourEmailsString.Split(new [] { ';' }, StringSplitOptions.RemoveEmptyEntries)
.GroupBy(emailAddressAttribute.IsValid);
This will give you 2 groups, the one with the Key == true will be valid email ids
var validEmailIds = groups.Where(group => group.Key)
.SelectMany(group => group);
the one with Key == false will be invalid email ids
var invalidEmailIds = groups.Where(group => !group.Key)
.SelectMany(group => group);
You could also run up a for loop after grouping, according to your needs..

Iterating whole list and updating string using ToLower - Not working

Technologies using.
C#
.NET 4.0
Visual Studio 2010
Problem.
I have a List<User> which contains an Email property. I want to lowercase all the email addresses within the list, but my implementation is not working. I'm using the following statement:
emails.ToList().ForEach(e => e.ToLower());
This didnt work at all for email addresses like Catherine.Burke#email.co.uk. I built the following to test this:
string email = "Catherine.Burke#email.co.uk";
email = email.ToLower();
Console.WriteLine("Email: " + email);
string email2 = "Catherine.Burke#email.co.uk";
string email3 = "Gareth.bradley#email.co.uk";
List<string> emails = new List<string>();
emails.Add(email2);
emails.Add(email3);
emails.ToList().ForEach(e => e.ToLower());
emails.ToList().ForEach(delegate(string e)
{
Console.WriteLine("ForEach deletegate : " + e);
});
List<EmailAddress> emailAddresses = new List<EmailAddress>();
emailAddresses.Add(new EmailAddress { FullAddress = "Catherine.Burke#email.co.uk" });
emailAddresses.Add(new EmailAddress { FullAddress = "Gareth.bradley#email.co.uk" });
emailAddresses.ToList().ForEach(e => e.FullAddress.ToLower());
emailAddresses.ToList().ForEach(delegate(EmailAddress e)
{
Console.WriteLine("EmailAddress delegate: " + e.FullAddress);
});
foreach (EmailAddress em in emailAddresses)
{
Console.WriteLine("Foreach Print: " + em.FullAddress);
}
Now I thought it might be the Culture and as these are names, it kept them uppercase, but when I used ToLower() on a singular string it worked. The above ran with the following output, as you can see the 1st line shows an email address with lowercase characters, whereas the implementation of the various List's I tried using ForEach() have not worked. I'm presuming my implementation of ForEach() is incorrect?

Making my comment an answer as requested:
Use a simple for-loop. List.ForEach is a method where you get the string as argument, you can't replace the whole reference there and since strings are immutable you can't change them either. You have to reassign the string returned from String.ToLower to your variable:
for(int i = 0; i < emails.Count; i++)
emails[i] = emails[i].ToLower();
Side-note: if you are making all emails lowercase to get a case-insensitive comparison it's better to use the String.Equals overload with the right StringComparison
string email1 = "Catherine.Burke#email.co.uk";
string email2 = "catherine.burke#email.co.uk";
if (String.Equals(email1, email2, StringComparison.InvariantCultureIgnoreCase))
{
// ...
}

emails.ToList().ForEach(e => e.ToLower()); does just call ToLower() but does not assign the result.
What you want is:
var lowerEmails = emails.Select(e => e.ToLower()).ToList();

Try this:
emailAddresses.ToList().ForEach(e => e.FullAddress = e.FullAdress.ToLower());
As weertzui altready mentions the ForEach-method simply calls the delegate. However the result of this action is not used in your code in any way.
However I´d strongly recommend to use a simply foreach:
foreach(var mail in emailadresses) mail.FullAdress = mail.FullAdress.ToLower();
which seems better readable to me.

replacing data in between specific characters

I have a string which has some keys between <<>>.
string s = "<p>Hi <<USER>>,<br/>How are you doing<br/>Regards,<br/><<SENDER>></p>";
I want to first fetch the key names USER and SENDER in a list which i did by:
var keys = new List<string>();
foreach (Match match in Regex.Matches(s, #"<<(.*?)>>"))
{
keys.Add(match.Groups[1].Value);
}
List<string> values= new List<string>(){"John","Team"};
After we get the keys,i want to replace these keys by another list(named values here) which has the values for these keys and want the result as:
string s = "<p>Hi John,<br/>How are you doing<br/>Regards,<br/>Team</p>";
The string s can be anything and the no of keys and their values could also vary but the keys will always be enclosed in between <<>>

As suggested by #AlexBell, you could simply use the String.Replace() method.
Further, it's more convenient to declare a collection of placeholder/value pairs, like so:
string s = "<p>Hi <<USER>>,<br/>How are you doing<br/>Regards,<br/><<SENDER>></p>";
Dictionary<string, string> dictionary = new Dictionary<string, string>();
dictionary.Add("<<USER>>", "Jhon");
dictionary.Add("<<SENDER>>", "Team");
StringBuilder text = new StringBuilder(s);
foreach (var entry in dictionary)
{
text.Replace(entry.Key, entry.Value);
}
Console.WriteLine(text.ToString());

This function will perform the replacements that you ask for, using Regex.Replace:
public static string ParseTemplate(string template, string username, string senderName)
{
template = Regex.Replace(template, #"<<USER>>", username);
return Regex.Replace(template, #"<<SENDER>>", senderName);
}
Example:
string s = "<p>Hi <<USER>>,<br/>How are you doing<br/>Regards,<br/><<SENDER>></p>";
ParseTemplate(s, "John", "Team").Dump();
Output:
<p>Hi John,<br/>How are you doing<br/>Regards,<br/>Team</p>
You can call this in a loop over your dictionary or list of names.

Your business logic is a bit unclear, so based on just qualified guess, you can apply standard .NET/C# String.Replace Method (String, String)
(re:https://msdn.microsoft.com/en-us/library/fk49wtc1%28v=vs.110%29.aspx), for example:
string s = "<p>Hi <<USER>>,<br/>How are you doing<br/>Regards,<br/><<SENDER>></p>".Replace("<USER>", "John").Replace("<SENDER>", "Team");
Hope this may help.

//First we have lists of values (users) and senders
List<string> values= new List<string>(){"John","Team"};
List<string> senders = new List<string>(){"John","Team"};
//Then we can join that list using string.join
var allUsers = string.Join(",", values);
var allSender = string.Join(",", senders);
//Next we will be replacing it in our string
var namedString = Regex.Replace(string, #"<<USER>>", allUsers);
var output = Regex.Replace(namedString , #"<<SENDER>>", allSender);

Parse file with multiples values lines C#

I have to parse a file that is constructed like this :
User: jcruz Name: Jules Last: Cruz Email: Some#email.com
User: jdoe Name: John Last: Doe Email: Some#email.com
User: pmartin Name: Pete Last: Martin Email: Some#email.com
User: rrichard Name: Reed Last: Richard Email: Some#email.com
I need to split every line taking just Name, Last Name and Email into an object of the type
var contact = new Conctact {
Name = fieldFromLine,
Last= fieldFromLine,
Email = fieldFromLine
}
So my problem is which tool use : String.Split or Regex.Split. and how to implement it.
Thank you very much...
This is what a Have done so far:
String archivo = ((FileDialog)sender).FileName;
using (TextReader sr = new StreamReader(archivo,Encoding.UTF8))
{
String line = String.Empty;
while ((line = sr.ReadLine()) != null )
{
string[] result = Regex.Split(line,"User:");
//How to get the other fields...
}
}

var result =File.ReadLines(fileName)
.Select(line => line.Split(new string[]{"User:", "Name:", "Last:", "Email:"}, StringSplitOptions.RemoveEmptyEntries))
.Select(parts => new Conctact(){ Name = parts[1], Last = parts[2], Email = parts[3] })
.ToArray();

try this:
public class contact
{
public string Name { get; set; }
public string Lname { get; set; }
public string Email { get; set; }
}
List<contact> contact = new List<contact>();
private void split()
{
var lines = File.ReadAllLines(#"txt file address");
foreach (var line in lines)
{
var splitline=line.Split(':');
string name = splitline[2].Replace("Last", "");
string lname = splitline[3].Replace("Email","");
contact.Add(new contact { Name = name, Lname = lname, Email = splitline[4] });
}
}

Answer: neither.
Use a simple finite-state machine parser to read the file because unless you can guarantee that the text values will never be "Name:" or "Last:" or "Email:" then you'll run into problems with string splitting. Also FSM-based parsers are significantly faster than string splitting (as there is no extraneous string allocation).
I don't have the time to write out an entire parser, but here's the simple logic:
enum State { InUser, InName, InLast, InEmail }
State currentState = State.InUser; // you start off with the 'cursor' in the "User" section
StringBuilder sb = new StringBuilder(); // this holds the current string element
foreach(Char c in entireTextFile) { // presumably using `StreamReader.Read()`
switch( currentState ) {
case InUser:
switch( c ) {
// state transition logic here
}
// append the character to the StringBuilder until you've identified and reached the next field, then save the sb value to the appropriat
case InName:
// and so on...
}
}
Of course, an FSM parser is fundamentally the same thing as a Regular Expression parser, but it means you get to code the state-transitions yourself rather than using RegEx's syntax which is faster, performance-wise.
If your project is small and don't care about performance, and can guarantee certain data formatting rules then I'd go with regex.
But never, ever, use String.Split to read a file.

Regex is overkill. Also note that some last names that contain spaces.
Contact c = new Contact();
string () tokens = input.Split(":".ToCharArray());
if (tokens.Count < 5)
return; // error
// now strip the last word from each token
c.Name = tokens(2).Substring(0, tokens(2).LastIndexOf(" ".ToCharArray())).Trim();
c.Last = tokens(3).Substring(0, tokens(3).LastIndexOf(" ".ToCharArray())).Trim();
c.Email = tokens(4).Trim();

extracting the common prefixes from a list of strings

I have a list of strings, such as:
{ abc001, abc002, abc003, cdef001, cdef002, cdef004, ghi002, ghi001 }
I want to get all the common unique prefixes; for example, for the above list:
{ abc, cdef, ghi }
How do I do that?

var list = new List<String> {
"abc001", "abc002", "abc003", "cdef001",
"cdef002", "cdef004", "ghi002", "ghi001"
};
var prefixes = list.Select(x = >Regex.Match(x, #"^[^\d]+").Value).Distinct();

It may be a good idea to write a helper class to represent your data. For example:
public class PrefixedNumber
{
private static Regex parser = new Regex(#"^(\p{L}+)(\d+)$");
public PrefixedNumber(string source) // you may want a static Parse method.
{
Match parsed = parser.Match(source); // think about an error here when it doesn't match
Prefix = parsed.Groups[1].Value;
Index = parsed.Groups[2].Value;
}
public string Prefix { get; set; }
public string Index { get; set; }
}
You need to come up with a better name, of course, and better access modifiers.
Now the task is quite easy:
List<string> data = new List<string> { "abc001", "abc002", "abc003", "cdef001",
"cdef002", "cdef004", "ghi002", "ghi001" };
var groups = data.Select(str => new PrefixedNumber(str))
.GroupBy(prefixed => prefixed.Prefix);
The result is all data, parsed, and grouped by the prefix.

You can achieve that using Regular Expression to select the text part, and then use HashSet<string> to add that text part so no duplication added:
using System.Text.RegularExpressions;
//simulate your real list
List<string> myList = new List<string>(new string[] { "abc001", "abc002", "cdef001" });
string pattern = #"^(\D*)\d+$";
// \D* any non digit characters, and \d+ means followed by at least one digit,
// Note if you want also to capture string like "abc" alone without followed by numbers
// then the pattern will be "^(\D*)$"
Regex regex = new Regex(pattern);
HashSet<string> matchesStrings = new HashSet<string>();
foreach (string item in myList)
{
var match = regex.Match(item);
if (match.Groups.Count > 1)
{
matchesString.Add(match.Groups[1].Value);
}
}
result:
abc, cde

Assuming that your prefix is all alpha characters and terminited by the first non-alpha character, you could use the following LINQ expression
List<string> listOfStrings = new List<String>()
{ "abc001d", "abc002", "abc003", "cdef001", "cdef002", "cdef004", "ghi002", "ghi001" };
var prefixes = (from s in listOfStrings
select new string(s.TakeWhile(c => char.IsLetter(c)).ToArray())).Distinct();