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Proper way in C# to combine an arbitrary number of strings into a single string

I breezed through the documentation for the string class and didn't see any good tools for combining an arbitrary number of strings into a single string. The best procedure I could come up with in my program is
string [] assetUrlPieces = { Server.MapPath("~/assets/"),
"organizationName/",
"categoryName/",
(Guid.NewGuid().ToString() + "/"),
(Path.GetFileNameWithoutExtension(file.FileName) + "/")
};
string assetUrl = combinedString(assetUrlPieces);
private string combinedString ( string [] pieces )
{
string alltogether = "";
foreach (string thispiece in pieces) alltogether += alltogether + thispiece;
return alltogether;
}
but that seems like too much code and too much inefficiency (from the string addition) and awkwardness.

If you want to insert a separator between values, string.Join is your friend. If you just want to concatenate the strings, then you can use string.Concat:
string assetUrl = string.Concat(assetUrlPieces);
That's marginally simpler (and possibly more efficient, but probably insignificantly) than calling string.Join with an empty separator.
As noted in comments, if you're actually building up the array at the same point in the code that you do the concatenation, and you don't need the array for anything else, just use concatenation directly:
string assetUrl = Server.MapPath("~/assets/") +
"organizationName/" +
"categoryName/" +
Guid.NewGuid() + "/" +
Path.GetFileNameWithoutExtension(file.FileName) + "/";
... or potentially use string.Format instead.

I prefer using string.Join:
var result = string.Join("", pieces);
You can read about string.Join on MSDN

You want a StringBuilder, I think.
var sb = new StringBuilder(pieces.Count());
foreach(var s in pieces) {
sb.Append(s);
}
return sb.ToString();
Update
#FiredFromAmazon.com: I think you'll want to go with the string.Concat solution offered by others for
Its sheer simplicity
Higher performance. Under the hood, it uses FillStringChecked, which does pointer copies, whereas string.Join uses StringBuilder. See http://referencesource.microsoft.com/#mscorlib/system/string.cs,1512. (Thank you to #Bas).

string.Concat is the most appropriate method for what you want.
var result = string.Concat(pieces);
Unless you want to put delimiters between the individual strings. Then you'd use string.Join
var result = string.Join(",", pieces); // comma delimited result.

A simple way to do this with a regular for loop:
(since you can use the indices, plus I like these loops better than foreach loops)
private string combinedString(string[] pieces)
{
string alltogether = "";
for (int index = 0; index <= pieces.Length - 1; index++) {
if (index != pieces.Length - 1) {
alltogether += string.Format("{0}/" pieces[index]);
}
}
return alltogether;

Parse multiple values from string c#

Suppose I have written "5 and 6" or "5+6". How can I assign 5 and 6 to two different variables in c# ?
P.S. I also want to do certain work if certain chars are found in string. Suppose I have written 5+5. Will this code do that ?
if(string.Contains("+"))
{
sum=x+y;
}

string input="5+5";
var numbers = Regex.Matches(input, #"\d+")
.Cast<Match>()
.Select(m => m.Value)
.ToList();

Personally, I would vote against doing some splitting and regular expression stuff.
Instead I would (and did in the past) use one of the many Expression Evaluation libraries, like e.g. this one over at Code Project (and the updated version over at CodePlex).
Using the parser/tool above, you could do things like:
A simple expression evaluation then could look like:
Expression e = new Expression("5 + 6");
Debug.Assert(11 == e.Evaluate());
To me this is much more error-proof than doing the parsing all by myself, including regular expressions and the like.

You should use another name for your string than string
var numbers = yourString.Split("+");
var sum = Convert.ToInt32(numbers[0]) + Convert.ToInt32(numbers[1]);
Note: Thats an implementation without any error checking or error handling...

If you want to assign numbers from string to variables, you will have to parse string and make conversion.
Simple example, if you have text with only one number
string text = "500";
int num = int.Parse(text);
Now, if you want to parse something more complicated, you can use split() and/or regex to get all numbers and operators between them. Than you just iterate array and assign numbers to variables.
string text = "500+400";
if (text.Contains("+"))
{
String[] data = text.Split("+");
int a = int.Parse(data[0]);
int b = int.Parse(data[1]);
int res = a + b;
}
Basicly, if you have just 2 numbers and operazor between them, its ok. If you want to make "calculator" you will need something more, like Binary Trees or Stack.

Use the String.Split method. It splits your string rom the given character and returns a string array containing the value that is broken down into multiple pieces depending on the character to break, in this case, its "+".
int x = 0;
int y = 0;
int z = 0;
string value = "5+6";
if (value.Contains("+"))
{
string[] returnedArray = value.Split('+');
x = Convert.ToInt32(returnedArray[0]);
y = Convert.ToInt32(returnedArray[1]);
z = x + y;
}

Something like this may helpful
string strMy = "5&6";
char[] arr = strMy.ToCharArray();
List<int> list = new List<int>();
foreach (char item in arr)
{
int value;
if (int.TryParse(item.ToString(), out value))
{
list.Add(item);
}
}
list will contains all the integer values

You can use String.Split method like;
string s = "5 and 6";
string[] a = s.Split(new string[] { "and", "+" }, StringSplitOptions.RemoveEmptyEntries);
Console.WriteLine(a[0].Trim());
Console.WriteLine(a[1].Trim());
Here is a DEMO.

Use regex to get those value and then switch on the operand to do the calculation
string str = "51 + 6";
str = str.Replace(" ", "");
Regex regex = new Regex(#"(?<rightHand>\d+)(?<operand>\+|and)(?<leftHand>\d+)");
var match = regex.Match(str);
int rightHand = int.Parse(match.Groups["rightHand"].Value);
int leftHand = int.Parse(match.Groups["leftHand"].Value);
string op = match.Groups["operand"].Value;
switch (op)
{
case "+":
.
.
.
}

Split function maybe is comfortable in use but it is space inefficient
because it needs array of strings
Maybe Trim(), IndexOf(), Substring() can replace Split() function

How to remove a duplicate set of characters in a string

For example a string contains the following (the string is variable):
http://www.google.comhttp://www.google.com
What would be the most efficient way of removing the duplicate url here - e.g. output would be:
http://www.google.com

I assume that input contains only urls.
string input = "http://www.google.comhttp://www.google.com";
// this will get you distinct URLs but without "http://" at the beginning
IEnumerable<string> distinctAddresses = input
.Split(new[] {"http://"}, StringSplitOptions.RemoveEmptyEntries)
.Distinct();
StringBuilder output = new StringBuilder();
foreach (string distinctAddress in distinctAddresses)
{
// when building the output, insert "http://" before each address so
// that it resembles the original
output.Append("http://");
output.Append(distinctAddress);
}
Console.WriteLine(output);

Efficiency has various definitions: code size, total execution time, CPU usage, space usage, time to write the code, etc. If you want to be "efficient", you should know which one of these you're trying for.
I'd do something like this:
string url = "http://www.google.comhttp://www.google.com";
if (url.Length % 2 == 0)
{
string secondHalf = url.Substring(url.Length / 2);
if (url.StartsWith(secondHalf))
{
url = secondHalf;
}
}
Depending on the kinds of duplicates you need to remove, this may or may not work for you.

collect strings into list and use distinct, if your string has http address you can apply regex http:.+?(?=((http:)|($)) with RegexOptions.SingleLine
var distinctList = list.Distinct(StringComparer.CurrentCultureIgnoreCase).ToList();

Given you don't know the length of the string, you don't know if something is double and you don't know what is double:
string yourprimarystring = "http://www.google.comhttp://www.google.com";
int firstCharacter;
string temp;
for(int i = 0; i <= yourprimarystring.length; i++)
{
for(int j = 0; j <= yourprimarystring.length; j++)
{
string search = yourprimarystring.substring(i,j);
firstCharacter = yourprimaryString.IndexOf(search);
if(firstCharacter != -1)
{
temp = yourprimarystring.substring(0,firstCharacter) + yourprimarystring.substring(firstCharacter + j - i,yourprimarystring.length)
yourprimarystring = temp;
}
}
This itterates through all your elements, takes all out from first to last letter and searches for them like this:
ABCDA - searches for A finds A exludes A, thats the problem, you need to specify how long the duplication needs to be if you want to make it variable, but maybe my code helps you.

How to extract string at a certain character that is repeated within string?

How can I get "MyLibrary.Resources.Images.Properties" and "Condo.gif" from a "MyLibrary.Resources.Images.Properties.Condo.gif" string.
I also need it to be able to handle something like "MyLibrary.Resources.Images.Properties.legend.House.gif" and return "House.gif" and "MyLibrary.Resources.Images.Properties.legend".
IndexOf LastIndexOf wouldn't work because I need the second to last '.' character.
Thanks in advance!
UPDATE
Thanks for the answers so far but I really need it to be able to handle different namespaces. So really what I'm asking is how to I split on the second to last character in a string?

You can use LINQ to do something like this:
string target = "MyLibrary.Resources.Images.Properties.legend.House.gif";
var elements = target.Split('.');
const int NumberOfFileNameElements = 2;
string fileName = string.Join(
".",
elements.Skip(elements.Length - NumberOfFileNameElements));
string path = string.Join(
".",
elements.Take(elements.Length - NumberOfFileNameElements));
This assumes that the file name part only contains a single . character, so to get it you skip the number of remaining elements.

You can either use a Regex or String.Split with '.' as the separator and return the second-to-last + '.' + last pieces.

You can look for IndexOf("MyLibrary.Resources.Images.Properties."), add that to MyLibrary.Resources.Images.Properties.".Length and then .Substring(..) from that position

If you know exactly what you're looking for, and it's trailing, you could use string.endswith. Something like
if("MyLibrary.Resources.Images.Properties.Condo.gif".EndsWith("Condo.gif"))
If that's not the case check out regular expressions. Then you could do something like
if(Regex.IsMatch("Condo.gif"))
Or a more generic way: split the string on '.' then grab the last two items in the array.

string input = "MyLibrary.Resources.Images.Properties.legend.House.gif";
//if string isn't already validated, make sure there are at least two
//periods here or you'll error out later on.
int index = input.LastIndexOf('.', input.LastIndexOf('.') - 1);
string first = input.Substring(0, index);
string second = input.Substring(index + 1);

Try splitting the string into an array, by separating it by each '.' character.
You will then have something like:
{"MyLibrary", "Resources", "Images", "Properties", "legend", "House", "gif"}
You can then take the last two elements.

Just break down and do it in a char loop:
int NthLastIndexOf(string str, char ch, int n)
{
if (n <= 0) throw new ArgumentException();
for (int idx = str.Length - 1; idx >= 0; --idx)
if (str[idx] == ch && --n == 0)
return idx;
return -1;
}
This is less expensive than trying to coax it using string splitting methods and isn't a whole lot of code.
string s = "1.2.3.4.5";
int idx = NthLastIndexOf(s, '.', 3);
string a = s.Substring(0, idx); // "1.2"
string b = s.Substring(idx + 1); // "3.4.5"

What is the best way to parse this string in C#?

I have a string that I am reading from another system. It's basically a long string that represents a list of key value pairs that are separated by a space in between. It looks like this:
key:value[space]key:value[space]key:value[space]
So I wrote this code to parse it:
string myString = ReadinString();
string[] tokens = myString.split(' ');
foreach (string token in tokens) {
string key = token.split(':')[0];
string value = token.split(':')[1];
. . . .
}
The issue now is that some of the values have spaces in them so my "simplistic" split at the top no longer works. I wanted to see how I could still parse out the list of key value pairs (given space as a separator character) now that I know there also could be spaces in the value field as split doesn't seem like it's going to be able to work anymore.
NOTE: I now confirmed that KEYs will NOT have spaces in them so I only have to worry about the values. Apologies for the confusion.

Use this regular expression:
\w+:[\w\s]+(?![\w+:])
I tested it on
test:testvalue test2:test value test3:testvalue3
It returns three matches:
test:testvalue
test2:test value
test3:testvalue3
You can change \w to any character set that can occur in your input.
Code for testing this:
var regex = new Regex(#"\w+:[\w\s]+(?![\w+:])");
var test = "test:testvalue test2:test value test3:testvalue3";
foreach (Match match in regex.Matches(test))
{
var key = match.Value.Split(':')[0];
var value = match.Value.Split(':')[1];
Console.WriteLine("{0}:{1}", key, value);
}
Console.ReadLine();
As Wonko the Sane pointed out, this regular expression will fail on values with :. If you predict such situation, use \w+:[\w: ]+?(?![\w+:]) as the regular expression. This will still fail when a colon in value is preceded by space though... I'll think about solution to this.

This cannot work without changing your split from a space to something else such as a "|".
Consider this:
Alfred Bester:Alfred Bester Alfred:Alfred Bester
Is this Key "Alfred Bester" & value Alfred" or Key "Alfred" & value "Bester Alfred"?

string input = "foo:Foobarius Maximus Tiberius Kirk bar:Barforama zap:Zip Brannigan";
foreach (Match match in Regex.Matches(input, #"(\w+):([^:]+)(?![\w+:])"))
{
Console.WriteLine("{0} = {1}",
match.Groups[1].Value,
match.Groups[2].Value
);
}
Gives you:
foo = Foobarius Maximus Tiberius Kirk
bar = Barforama
zap = Zip Brannigan

You could try to Url encode the content between the space (The keys and the values not the : symbol) but this would require that you have control over the Input Method.
Or you could simply use another format (Like XML or JSON), but again you will need control over the Input Format.
If you can't control the input format you could always use a Regular expression and that searches for single spaces where a word plus : follows.
Update (Thanks Jon Grant)
It appears that you can have spaces in the key and the value. If this is the case you will need to seriously rethink your strategy as even Regex won't help.

string input = "key1:value key2:value key3:value";
Dictionary<string, string> dic = input.Split(' ').Select(x => x.Split(':')).ToDictionary(x => x[0], x => x[1]);
The first will produce an array:
"key:value", "key:value"
Then an array of arrays:
{ "key", "value" }, { "key", "value" }
And then a dictionary:
"key" => "value", "key" => "value"
Note, that Dictionary<K,V> doesn't allow duplicated keys, it will raise an exception in such a case. If such a scenario is possible, use ToLookup().

Using a regular expression can solve your problem:
private void DoSplit(string str)
{
str += str.Trim() + " ";
string patterns = #"\w+:([\w+\s*])+[^!\w+:]";
var r = new System.Text.RegularExpressions.Regex(patterns);
var ms = r.Matches(str);
foreach (System.Text.RegularExpressions.Match item in ms)
{
string[] s = item.Value.Split(new char[] { ':' });
//Do something
}
}

This code will do it (given the rules below). It parses the keys and values and returns them in a Dictonary<string, string> data structure. I have added some code at the end that assumes given your example that the last value of the entire string/stream will be appended with a [space]:
private Dictionary<string, string> ParseKeyValues(string input)
{
Dictionary<string, string> items = new Dictionary<string, string>();
string[] parts = input.Split(':');
string key = parts[0];
string value;
int currentIndex = 1;
while (currentIndex < parts.Length-1)
{
int indexOfLastSpace=parts[currentIndex].LastIndexOf(' ');
value = parts[currentIndex].Substring(0, indexOfLastSpace);
items.Add(key, value);
key = parts[currentIndex].Substring(indexOfLastSpace + 1);
currentIndex++;
}
value = parts[parts.Length - 1].Substring(0,parts[parts.Length - 1].Length-1);
items.Add(key, parts[parts.Length-1]);
return items;
}
Note: this algorithm assumes the following rules:
No spaces in the values
No colons in the keys
No colons in the values

Without any Regex nor string concat, and as an enumerable (it supposes keys don't have spaces, but values can):
public static IEnumerable<KeyValuePair<string, string>> Split(string text)
{
if (text == null)
yield break;
int keyStart = 0;
int keyEnd = -1;
int lastSpace = -1;
for(int i = 0; i < text.Length; i++)
{
if (text[i] == ' ')
{
lastSpace = i;
continue;
}
if (text[i] == ':')
{
if (lastSpace >= 0)
{
yield return new KeyValuePair<string, string>(text.Substring(keyStart, keyEnd - keyStart), text.Substring(keyEnd + 1, lastSpace - keyEnd - 1));
keyStart = lastSpace + 1;
}
keyEnd = i;
continue;
}
}
if (keyEnd >= 0)
yield return new KeyValuePair<string, string>(text.Substring(keyStart, keyEnd - keyStart), text.Substring(keyEnd + 1));
}

I guess you could take your method and expand upon it slightly to deal with this stuff...
Kind of pseudocode:
List<string> parsedTokens = new List<String>();
string[] tokens = myString.split(' ');
for(int i = 0; i < tokens.Length; i++)
{
// We need to deal with the special case of the last item,
// or if the following item does not contain a colon.
if(i == tokens.Length - 1 || tokens[i+1].IndexOf(':' > -1)
{
parsedTokens.Add(tokens[i]);
}
else
{
// This bit needs to be refined to deal with values with multiple spaces...
parsedTokens.Add(tokens[i] + " " + tokens[i+1]);
}
}
Another approach would be to split on the colon... That way, your first array item would be the name of the first key, second item would be the value of the first key and then name of the second key (can use LastIndexOf to split it out), and so on. This would obviously get very messy if the values can include colons, or the keys can contain spaces, but in that case you'd be pretty much out of luck...