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How to do a multiple case insensitive replace using a StringBuilder

I have a (large) template and want to replace multiple values. The replacement needs to be done case insensitive. It must also be possible to have keys that does not exist in the template.
For example:
[TestMethod]
public void ReplaceMultipleWithIgnoreCaseText()
{
const string template = "My name is #Name# and I like to read about #SUBJECT# on #website#, tag #subject#";
const string expected = "My name is Alex and I like to read about C# on stackoverflow.com, tag C#";
var replaceParameters = new List<KeyValuePair<string, string>>
{
new KeyValuePair<string, string>("#name#","Alex"),
new KeyValuePair<string, string>("#subject#","C#"),
new KeyValuePair<string, string>("#website#","stackoverflow.com"),
// Note: The next key does not exist in template
new KeyValuePair<string, string>("#country#","The Netherlands"),
};
var actual = ReplaceMultiple(template, replaceParameters);
Assert.AreEqual(expected, actual);
}
public string ReplaceMultiple(
string template,
IEnumerable<KeyValuePair<string, string>> replaceParameters)
{
throw new NotImplementedException(
"Implementation needed for many parameters and long text.");
}
Note that if I have a list of 30 parameters and a large template, I do not want 30 large strings in memory. Using a StringBuilder seems to be an option, but other solutions are also welcome.
Solution I tried but did not work
Solution found here (C# String replace with dictionary) throws an exception when a key is not in the colletion, but our users makes mistakes and in that case I want to just leave the wromg key in the text. Example:
static readonly Regex re = new Regex(#"\$(\w+)\$", RegexOptions.Compiled);
static void Main2()
{
// "Name" is accidentally typed by a user as "nam".
string input = #"Dear $nam$, as of $date$ your balance is $amount$";
var args = new Dictionary<string, string>(
StringComparer.OrdinalIgnoreCase) {
{"name", "Mr Smith"},
{"date", "05 Aug 2009"},
{"amount", "GBP200"}};
// Works, but not case insensitive and
// uses a lot of memory when using a large template
// ReplaceWithDictionary many args
string output1 = input;
foreach (var arg in args)
{
output1 = output1.Replace("$" + arg.Key +"$", arg.Value);
}
// Throws a KeyNotFoundException + Only works when data is tokenized
string output2 = re.Replace(input, match => args[match.Groups[1].Value]);
}

Using a StringBuilder seems to be an option, but other solutions are also welcome.
Since you want case insensitive, I'd suggest (non StringBuilder):
public static string ReplaceMultiple(
string template,
IEnumerable<KeyValuePair<string, string>> replaceParameters)
{
var result = template;
foreach(var replace in replaceParameters)
{
var templateSplit = Regex.Split(result,
replace.Key,
RegexOptions.IgnoreCase);
result = string.Join(replace.Value, templateSplit);
}
return result;
}
DotNetFiddle Example

This is based off of Marc's answer the only real change is the check during the replacement and the boundary regex rule:
static readonly Regex re = new Regex(#"\b(\w+)\b", RegexOptions.Compiled);
static void Main(string[] args)
{
string input = #"Dear Name, as of dAte your balance is amounT!";
var replacements = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)
{
{"name", "Mr Smith"},
{"date", "05 Aug 2009"},
{"amount", "GBP200"}
};
string output = re.Replace(input, match => replacements.ContainsKey(match.Groups[1].Value) ? replacements[match.Groups[1].Value] : match.Groups[1].Value);
}
And here is a 5000 iterations test benchmark, have not looked at memory or anything else.
Replacement function is the one you have checked as the accepted answer.

I think I might have something you could try. I used something similar to it for email templates
public string replace()
{
string appPath = Request.PhysicalApplicationPath;
StreamReader sr = new StreamReader(appPath + "EmailTemplates/NewMember.txt");
string template = sr.ReadToEnd();
template = template.Replace("<%Client_Name%>",
first_name.Text + " " + middle_initial.Text + " " + last_name.Text);
//Add Customer data
template = template.Replace("<%Client_First_Name%>", first_name.Text);
template = template.Replace("<%Client_MI%>", middle_initial.Text);
template = template.Replace("<%Client_Last_Name%>", last_name.Text);
template = template.Replace("<%Client_DOB%>", dob.Text);
return template;
}
Inside of your template you can have tags such as <% %> as place holders for the values you want
Hope this helps!

The answer of Marc Gravell: C# String replace with dictionary can be changed an little bit so it does not throws an exception when the match can not be found. In this case it simply does not replace the match.
In case the string to be replace is tokenized, this is the solution:
static readonly Regex RegExInstance = new Regex(#"\$(\w+)\$", RegexOptions.Compiled);
public string ReplaceWithRegEx(string template, Dictionary<string, string> parameters)
{
return RegExInstance.Replace(template, match => GetNewValue(parameters, match));
}
private string GetNewValue(Dictionary<string, string> parameters, Match match)
{
var oldValue = match.Groups[1].Value;
string newValue;
var found = parameters.TryGetValue(oldValue, out newValue);
if (found)
{
return newValue;
}
var originalValue = match.Groups[0].Value;
return originalValue;
}
I have tested the solution with a 100.000 bytes string, 7 keys and hundreds of replacements. It uses 7 times more memory then the lenght of the string. And it took only 0.002 seconds.

Assign the entire QueryString to a String?

I've passed a really long Query String from one page to another in my Windows Phone 8 project.
I need to pass these parameters from the new page to another page but don't want to reconstruct he entire QueryString.
Is there a way to assign the entire QueryString to a new String?
Something like
String newQuery = NavigationContext.QueryString.ToString();

I need to pass these parameters from the new page to another page but
don't want to reconstruct the entire QueryString
Why not? This is programming: do all the work in one place so you don't have to do it again later. Let's use an extension method to do this.
Silverlight
Place this code in a static class...
public string ToQueryString(this IDictionary dict)
{
string querystring = "";
foreach(string key in dict.AllKeys)
{
querystring += key + "=" + dict[key] + "&";
}
return querystring;
}
Use it like this...
string QueryString = NavigationContext.QueryString.ToQueryString();
ASP.NET
When I originally read this question, I thought it was for ASP.NET, not Silverlight. I'll leave the ASP.NET answer here in case someone stumbles across it looking for how to do it in ASP.NET.
public string ToQueryString(this NameValueCollection qs)
{
string querystring = "";
foreach(string key in qs.AllKeys)
{
querystring += key + "=" + qs[key] + "&";
}
return querystring;
}
Use it like this...
string QueryString = Request.QueryString.ToQueryString();
There is something that already exists for ASP.NET. But I feel it's important to demonstrate that you can do all the work once somewhere. Then not have to do it again. If you want to use a built-in way, something like this would work, using the Query property of the Uri class.
string QueryString = System.Web.HttpContext.Current.Request.Url.Query;

Here's a way that may be a little simpler...
You could project the results into a format of your choosing. Here's a simple example below.
I've used an IDictionary<string,string> as it is the underlying type for NavigationContext.QueryString
var test = new Dictionary<String,String>();
test.Add("1", "one");
test.Add("2", "two");
test.Add("3", "three");
// Choose any string format you wish and project to array
var newArray = test.Select(item => item.Key + ":" + item.Value).ToArray();
// Join on any separator
string output = String.Join(",", newArray);
This still means that you have to interpret the result later (according to the format you chose). Here you'll get a format like
"1:one,2:two,3:three"

If you've sent it as a querystring just pull it back out on the OnNavigatedTo() Method and then you can store the query in the page until you move on?.
string newQuery;
protected override void OnNavigatedTo(NavigationEventArgs e)
{
newQuery = NavigationContext.QueryString["queryName"];
}

Try this:
public string GetQueryString()
{
IDictionary<String, String> NavigationContextData = NavigationContext.QueryString;
string data = "/Pagename.xaml?";
foreach (var item in NavigationContextData)
{
data += item.Key + "=" + item.Value + "&";
}
data = data.Substring(0, data.Length - 1);
return data;
}

If it's in your OnNavigatedTo() event, you can use a quick, easy two-liner. This can be condensed to a single line or expanded to check for the existence of the ? character. If you know that there are always parameters passed, the check is unnecessary and these two lines work fine:
string QStr = e.Uri.ToString();
string ParmStr = QStr.Substring(QStr.IndexOf('?') + 1);
You can also condense it into a single line:
string ParmStr = e.Uri.ToString().Substring(e.Uri.ToString().IndexOf('?') + 1);

Parse URL array parameters into C# Dictionaries

I have the following code to parse key value pairs from URLs:
public static NameValueCollection ParseQueryString(String query)
{
NameValueCollection queryParameters = new NameValueCollection();
string[] querySegments = query.Split('&');
foreach (string segment in querySegments)
{
string[] parts = segment.Split('=');
if (parts.Length > 0)
{
string key = parts[0].Trim(new char[] { '?', ' ' });
string val = parts[1].Trim();
queryParameters.Add(key, val);
}
}
return queryParameters;
}
I am using this function like this:
args = ParseQueryString("alpha=1&beta=bbbb&array%5B0%5D%5Ba%5D=1&array%5B0%5D%5Bb%5D=2&array%5B1%5D%5Ba%5D=1&array%5B1%5D%5Bb%5D=2&array%5B%5D=3&array%5B%5D=4");
foreach (var k in args.AllKeys)
{
tw.WriteLine(k + ": " + args[k]);
}
Output:
alpha: 1
beta: bbbb
array[0][a]: 1
array[0][b]: 2
array[1][a]: 1
array[1][b]: 2
array[]: 3,4
I need an output of nested NameValueCollections or nested Dictionaries, so I can access the values somethis like this:
args = ParseQueryString("alpha=1&beta=bbbb&array%5B0%5D%5Ba%5D=1&array%5B0%5D%5Bb%5D=2&array%5B1%5D%5Ba%5D=1&array%5B1%5D%5Bb%5D=2&array%5B%5D=3&array%5B%5D=4");
var item = args.Get("array").Get(0).Get("b"); // will be "2"
What is the most elegant method to achieve this? I would prefer a solution without System.Web or any extra reference.

If you use the ASP.NET MVC Framework, the default MVC parameter binder can deal with it automatically in the following way:
// GetData?filters[0][field]=fieldName&filters[0][type]=number&filters[0][value]=3
public ActionResult GetData(IEnumerable<Dictionary<string,string>> filters)
{
// todo
}
For more info and examples check out this blog post that I wrote on this topic.

Easiest way to parse "querystring" formatted data

With the following code:
string q = "userID=16555&gameID=60&score=4542.122&time=343114";
What would be the easiest way to parse the values, preferably without writing my own parser? I'm looking for something with the same functionality as Request.querystring["gameID"].

Pretty easy... Use the HttpUtility.ParseQueryString method.
Untested, but this should work:
var qs = "userID=16555&gameID=60&score=4542.122&time=343114";
var parsed = HttpUtility.ParseQueryString(qs);
var userId = parsed["userID"];
// ^^^^^^ Should be "16555". Note this will be a string of course.

You can do it with linq like this.
string query = "id=3123123&userId=44423&format=json";
Dictionary<string,string> dicQueryString =
query.Split('&')
.ToDictionary(c => c.Split('=')[0],
c => Uri.UnescapeDataString(c.Split('=')[1]));
string userId = dicQueryString["userID"];
Edit
If you can use HttpUtility.ParseQueryString then it will be a lot more straight forward and it wont be case-sensitive as in case of LinQ.

As has been mentioned in each of the previous answers, if you are in a context where you can add a dependency to the System.Web library, using HttpUtility.ParseQueryString makes sense. (For reference, the relevant source can be found in the Microsoft Reference Source). However, if this is not possible, I would like to propose the following modification to Adil's answer which accounts for many of the concerns addressed in the comments (such as case sensitivity and duplicate keys):
var q = "userID=16555&gameID=60&score=4542.122&time=343114";
var parsed = q.TrimStart('?')
.Split(new[] { '&' }, StringSplitOptions.RemoveEmptyEntries)
.Select(k => k.Split('='))
.Where(k => k.Length == 2)
.ToLookup(a => a[0], a => Uri.UnescapeDataString(a[1])
, StringComparer.OrdinalIgnoreCase);
var userId = parsed["userID"].FirstOrDefault();
var time = parsed["TIME"].Select(v => (int?)int.Parse(v)).FirstOrDefault();

If you want to avoid the dependency on System.Web that is required to use HttpUtility.ParseQueryString, you could use the Uri extension method ParseQueryString found in System.Net.Http.
Note that you have to convert the response body to a valid Uri so that ParseQueryString works.
Please also note in the MSDN document, this method is an extension method for the Uri class, so you need reference the assembly System.Net.Http.Formatting (in System.Net.Http.Formatting.dll). I tried installed it by the nuget package with the name "System.Net.Http.Formatting", and it works fine.
string body = "value1=randomvalue1&value2=randomValue2";
// "http://localhost/query?" is added to the string "body" in order to create a valid Uri.
string urlBody = "http://localhost/query?" + body;
NameValueCollection coll = new Uri(urlBody).ParseQueryString();

How is this
using System.Text.RegularExpressions;
// query example
// "name1=value1&name2=value2&name3=value3"
// "?name1=value1&name2=value2&name3=value3"
private Dictionary<string, string> ParseQuery(string query)
{
var dic = new Dictionary<string, string>();
var reg = new Regex("(?:[?&]|^)([^&]+)=([^&]*)");
var matches = reg.Matches(query);
foreach (Match match in matches) {
dic[match.Groups[1].Value] = Uri.UnescapeDataString(match.Groups[2].Value);
}
return dic;
}

System.Net.Http ParseQueryString extension method worked for me. I'm using OData query options and trying to parse out some custom parameters.
options.Request.RequestUri.ParseQueryString();
Seems to give me what I need.

HttpUtility.ParseQueryString will work as long as you are in a web app or don't mind including a dependency on System.Web. Another way to do this is:
// NameValueCollection nameValueCollection = HttpUtility.ParseQueryString(queryString);
NameValueCollection nameValueCollection = new NameValueCollection();
string[] querySegments = queryString.Split('&');
foreach(string segment in querySegments)
{
string[] parts = segment.Split('=');
if (parts.Length > 0)
{
string key = parts[0].Trim(new char[] { '?', ' ' });
string val = parts[1].Trim();
nameValueCollection.Add(key, val);
}
}

For .NET Core there is Microsoft.AspNetCore.WebUtilities.QueryHelpers.ParseQuery
var queryString = QueryHelpers.ParseQuery("?param1=value");
var queryParamValue = queryString["param1"];
Code snippet modified from trackjs.com:

A clean way of generating QueryString parameters for web requests

I came across a problem in my current application that required fiddling with the query string in a base Page class (which all my pages inherit from) to solve the problem. Since some of my pages use the query string I was wondering if there is any class that provides clean and simple query string manipulation.
Example of code:
// What happens if I want to future manipulate the query string elsewhere
// (e.g. maybe rewrite when the request comes back in)
// Or maybe the URL already has a query string (and the ? is invalid)
Response.Redirect(Request.Path + "?ProductID=" + productId);

Use HttpUtility.ParseQueryString, as someone suggested (and then deleted).
This will work, because the return value from that method is actually an HttpValueCollection, which inherits NameValueCollection (and is internal, you can't reference it directly). You can then set the names/values in the collection normally (including add/remove), and call ToString -- which will produce the finished querystring, because HttpValueCollection overrides ToString to reproduce an actual query string.

I was hoping to find a solution built into the framework but didn't. (those methods that are in the framework require to much work to make it simple and clean)
After trying several alternatives I currently use the following extension method: (post a better solution or comment if you have one)
public static class UriExtensions
{
public static Uri AddQuery(this Uri uri, string name, string value)
{
string newUrl = uri.OriginalString;
if (newUrl.EndsWith("&") || newUrl.EndsWith("?"))
newUrl = string.Format("{0}{1}={2}", newUrl, name, value);
else if (newUrl.Contains("?"))
newUrl = string.Format("{0}&{1}={2}", newUrl, name, value);
else
newUrl = string.Format("{0}?{1}={2}", newUrl, name, value);
return new Uri(newUrl);
}
}
This extension method makes for very clean redirection and uri manipulation:
Response.Redirect(Request.Url.AddQuery("ProductID", productId).ToString());
// Will generate a URL of www.google.com/search?q=asp.net
var url = new Uri("www.google.com/search").AddQuery("q", "asp.net")
and will work for the following Url's:
"http://www.google.com/somepage"
"http://www.google.com/somepage?"
"http://www.google.com/somepage?OldQuery=Data"
"http://www.google.com/somepage?OldQuery=Data&"

Note that whatever route you use, you should really encode the values - Uri.EscapeDataString should do that for you:
string s = string.Format("http://somesite?foo={0}&bar={1}",
Uri.EscapeDataString("&hehe"),
Uri.EscapeDataString("#mwaha"));

What I usually do is just rebuild the querystring. Request has a QueryString collection.
You can iterator over that to get the current (unencoded) parameters out, and just join them together (encoding as you go) with the appropriate separators.
The advantage is that Asp.Net has done the original parsing for you, so you don't need to worry about edge cases such as trailing & and ?s.

I find my way for easy manipulating with get parameters.
public static string UrlFormatParams(this string url, string paramsPattern, params object[] paramsValues)
{
string[] s = url.Split(new string[] {"?"}, StringSplitOptions.RemoveEmptyEntries);
string newQueryString = String.Format(paramsPattern, paramsValues);
List<string> pairs = new List<string>();
NameValueCollection urlQueryCol = null;
NameValueCollection newQueryCol = HttpUtility.ParseQueryString(newQueryString);
if (1 == s.Length)
{
urlQueryCol = new NameValueCollection();
}
else
{
urlQueryCol = HttpUtility.ParseQueryString(s[1]);
}
for (int i = 0; i < newQueryCol.Count; i++)
{
string key = newQueryCol.AllKeys[i];
urlQueryCol[key] = newQueryCol[key];
}
for (int i = 0; i < urlQueryCol.Count; i++)
{
string key = urlQueryCol.AllKeys[i];
string pair = String.Format("{0}={1}", key, urlQueryCol[key]);
pairs.Add(pair);
}
newQueryString = String.Join("&", pairs.ToArray());
return String.Format("{0}?{1}", s[0], newQueryString);
}
Use it like
"~/SearchInHistory.aspx".UrlFormatParams("t={0}&s={1}", searchType, searchString)

Check This!!!
// First Get The Method Used by Request i.e Get/POST from current Context
string method = context.Request.HttpMethod;
// Declare a NameValueCollection Pair to store QueryString parameters from Web Request
NameValueCollection queryStringNameValCollection = new NameValueCollection();
if (method.ToLower().Equals("post")) // Web Request Method is Post
{
string contenttype = context.Request.ContentType;
if (contenttype.ToLower().Equals("application/x-www-form-urlencoded"))
{
int data = context.Request.ContentLength;
byte[] bytData = context.Request.BinaryRead(context.Request.ContentLength);
queryStringNameValCollection = context.Request.Params;
}
}
else // Web Request Method is Get
{
queryStringNameValCollection = context.Request.QueryString;
}
// Now Finally if you want all the KEYS from QueryString in ArrayList
ArrayList arrListKeys = new ArrayList();
for (int index = 0; index < queryStringNameValCollection.Count; index++)
{
string key = queryStringNameValCollection.GetKey(index);
if (!string.IsNullOrEmpty(key))
{
arrListKeys.Add(key.ToLower());
}
}