Related
I have a string which has two tokens that bound a substring that I want to extract, but the substring may contain the tokens themselves, so I want between the 1st occurrence of token A and the last occurrence of token B. I also need to search for the tokens in a case-insensitive search.
Tried to wrap my head around using regex to get this, but can't seem to figure it out. Not sure the best approach here. String.split won't work.
I can't modify the casing of the data between the tokens in the string.
Try this, (I've made it into an extension method)
public static string Between(this string value, string a, string b)
{
int posA = value.IndexOf(a);
int posB = value.LastIndexOf(b);
if (posA == -1) || (posB == -1)
{
return "";
}
int adjustedPosA = posA + a.Length;
return (adjustedPosA >= posB) ? "" : value.Substring(adjustedPosA, posB - adjustedPosA);
}
Usage would be:
var myString = "hereIsAToken_andThisIsWhatIwant_andSomeOtherToken";
var whatINeed = myString.Between("hereIsAToken_", "_andSomeOtherToken");
An easy way to approach this problem is the use of the indexOf function provided by the string class. IndexOf returns the first occurence, lastIndexOf as the name suggests, the last one.
string data;
string token1;
string token2;
int start = data.IndexOf(token1)+token1.Length;
int end = data.LastIndexOf(token2);
string result = data.Substring(start, end-start);
From my personal point of view, regex might be a bit overkill here, just try my example :)
I have an input string. I need to replace its prefix (until first dot) with an other string.
The method signature:
string MyPrefixReplace(string input, string replacer)
Examples:
string res = MyPrefixReplace("12.345.6789", "000")
res = "000.345.6789";
res = MyPrefixReplace("908.345.6789", "1")
res = "1.345.6789";
Is there a way not to extract a sub-string before first dot and make a Replace**?
I.e - I don't want this solution
int i = input.IndexOf(".");
string rep = input.Substring(0,i);
input.Replace(rep,replacer);
Thanks
You could use String.Split
public string MyPrefixReplace(string source, string value, char delimiter = '.')
{
var parts = source.Split(delimiter);
parts[0] = value;
return String.Join(delimiter.ToString(), parts);
}
Live demo
Using String.IndexOf and String.Substring ist the most efficient way. In your approach you have used the wrong overload of Substring. String.Replace is pointless anyway since you don't want to replace all occurences of the first part but only the first part.
Therefore you don't have to take but to skip the the first part and prefix another. This works as desired:
public static string MyPrefixReplace(string input, string replacer, char prefixChar = '.')
{
int index = input.IndexOf(prefixChar);
if (index == -1)
return input;
return replacer + input.Substring(index);
}
Your input:
string result = MyPrefixReplace("908.345.6789", "1"); // 1.345.6789
result = MyPrefixReplace("12.345.6789", "000"); // 000.345.6789
Personally, I'd split the string up to get around this problem, although there's obviously other ways of doing this, this would be my approach:
string Input = "123.456.789"
string[] SplitInput = Input.Split('.');
SplitInput[0] = "321";
string Output = String.Join('.', SplitInput);
Output should be "321.456.789".
Hope somebody has a good idea. I have strings like this:
abcdefg
abcde
abc
What I need is for them to be trucated to show like this if more than a specified lenght:
abc ..
abc ..
abc
Is there any simple C# code I can use for this?
Here is the logic wrapped up in an extension method:
public static string Truncate(this string value, int maxChars)
{
return value.Length <= maxChars ? value : value.Substring(0, maxChars) + "...";
}
Usage:
var s = "abcdefg";
Console.WriteLine(s.Truncate(3));
All very good answers, but to clean it up just a little, if your strings are sentences, don't break your string in the middle of a word.
private string TruncateForDisplay(this string value, int length)
{
if (string.IsNullOrEmpty(value)) return string.Empty;
var returnValue = value;
if (value.Length > length)
{
var tmp = value.Substring(0, length) ;
if (tmp.LastIndexOf(' ') > 0)
returnValue = tmp.Substring(0, tmp.LastIndexOf(' ') ) + " ...";
}
return returnValue;
}
public string TruncString(string myStr, int THRESHOLD)
{
if (myStr.Length > THRESHOLD)
return myStr.Substring(0, THRESHOLD) + "...";
return myStr;
}
Ignore the naming convention it's just in case he actually needs the THRESHOLD variable or if it's always the same size.
Alternatively
string res = (myStr.Length > THRESHOLD) ? myStr.Substring(0, THRESHOLD) + ".." : myStr;
Here's a version that accounts for the length of the ellipses:
public static string Truncate(this string value, int maxChars)
{
const string ellipses = "...";
return value.Length <= maxChars ? value : value.Substring(0, maxChars - ellipses.Length) + ellipses;
}
There isn't a built in method in the .NET Framework which does this, however this is a very easy method to write yourself. Here are the steps, try making it yourself and let us know what you come up with.
Create a method, perhaps an extension method public static void TruncateWithEllipsis(this string value, int maxLength)
Check to see if the passed in value is greater than the maxLength specified using the Length property. If the value not greater than maxLength, just return the value.
If we didn't return the passed in value as is, then we know we need to truncate. So we need to get a smaller section of the string using the SubString method. That method will return a smaller section of a string based on a specified start and end value. The end position is what was passed in by the maxLength parameter, so use that.
Return the sub section of the string plus the ellipsis.
A great exercise for later would be to update the method and have it break only after full words. You can also create an overload to specify how you would like to show a string has been truncated. For example, the method could return " (click for more)" instead of "..." if your application is set up to show more detail by clicking.
Code behind:
string shorten(sting s)
{
//string s = abcdefg;
int tooLongInt = 3;
if (s.Length > tooLongInt)
return s.Substring(0, tooLongInt) + "..";
return s;
}
Markup:
<td><%= shorten(YOUR_STRING_HERE) %></td>
Maybe it is better to implement a method for that purpose:
string shorten(sting yourStr)
{
//Suppose you have a string yourStr, toView and a constant value
string toView;
const int maxView = 3;
if (yourStr.Length > maxView)
toView = yourStr.Substring(0, maxView) + " ..."; // all you have is to use Substring(int, int) .net method
else
toView = yourStr;
return toView;
}
I found this question after searching for "C# truncate ellipsis". Using various answers, I created my own solution with the following features:
An extension method
Add an ellipsis
Make the ellipsis optional
Validate that the string is not null or empty before attempting to truncate it.
public static class StringExtensions
{
public static string Truncate(this string value,
int maxLength,
bool addEllipsis = false)
{
// Check for valid string before attempting to truncate
if (string.IsNullOrEmpty(value)) return value;
// Proceed with truncating
var result = string.Empty;
if (value.Length > maxLength)
{
result = value.Substring(0, maxLength);
if (addEllipsis) result += "...";
}
else
{
result = value;
}
return result;
}
}
I hope this helps someone else.
string s = "abcdefg";
if (s.length > 3)
{
s = s.substring(0,3);
}
You can use the Substring function.
Refactor with new C# features just for disclosure:
Nullables (C# 7)
Expression-bodied members (C# 6 and 7)
Ranges on strings (C# 8)
// public static class StringExtensions { ...
private static string? Truncate(this string? value, int maxChars)
=>
string.IsNullOrEmpty(value) ? value :
value.Length <= maxChars ? value :
value[..maxChars] + "...";
Checked as "Community wiki", be free to improve answer.
Sure, here is some sample code:
string str = "abcdefg";
if (str.Length > X){
str = str.Substring(0, X) + "...";
}
I has this problem recently. I was storing a "status" message in a nvarcharMAX DB field which is 4000 characters. However my status messages were building up and hitting the exception.
But it wasn't a simple case of truncation as an arbitrary truncation would orphan part of a status message, so I really needed to "truncate" at a consistent part of the string.
I solved the problem by converting the string to a string array, removing the first element and then restoring to a string. Here is the code ("CurrentStatus" is the string holding the data)...
if (CurrentStatus.Length >= 3750)
{
// perform some truncation to free up some space.
// Lets get the status messages into an array for processing...
// We use the period as the delimiter, then skip the first item and re-insert into an array.
string[] statusArray = CurrentStatus.Split(new string[] { "." }, StringSplitOptions.None)
.Skip(1).ToArray();
// Next we return the data to a string and replace any escaped returns with proper one.
CurrentStatus = (string.Join(".", statusArray))
.Replace("\\r\\n", Environment.NewLine);
}
Hope it helps someone out.
2 days ago, there was a question related to string.LastIndexOf(String.Empty) returning the last index of string:
Do C# strings end with empty string?
So I thought that; a string can always contain string.empty between characters like:
"testing" == "t" + String.Empty + "e" + String.Empty +"sting" + String.Empty;
After this, I wanted to test if String.IndexOf(String.Empty) was returning 0 because since String.Empty can be between any char in a string, that would be what I expect it to return and I wasn't wrong.
string testString = "testing";
int index = testString.LastIndexOf(string.Empty); // index is 6
index = testString.IndexOf(string.Empty); // index is 0
It actually returned 0. I started to think that if I could split a string with String.Empty, I would get at least 2 string and those would be String.Empty and rest of the string since String.IndexOf(String.Empty) returned 0 and String.LastIndexOf(String.Empty) returned length of the string.. Here is what I coded:
string emptyString = string.Empty;
char[] emptyStringCharArr = emptyString.ToCharArray();
string myDummyString = "abcdefg";
string[] result = myDummyString.Split(emptyStringCharArr);
The problem here is, I can't obviously convert String.Empty to char[] and result in an empty string[]. I would really love to see the result of this operation and the reason behind this. So my questions are:
Is there any way to split a string with String.Empty?
If it is not possible but in an absolute world which it would be possible, would it return an array full of chars like [0] = "t" [1] = "e" [2] = "s" and so on or would it just return the complete string? Which would make more sense and why?
Yes, you can split any string with string .Empty
string[] strArr = s.Split(string.Empty.ToCharArray());
You will always get an Index of 0 when you look for String.Empty in any String, because it's the definition of String.IndexOf(String.Empty) you should have a look at the MSDN, where it says:
"The zero-based index position of
value if that string is found, or -1
if it is not. If value is
String.Empty, the return value is 0."
Directed to your second Question:
I think you can Split a String with an Empty String by doing something like this in your code:
String test = "fwewfeoj";
test.Split(new String[] { String.Empty }, StringSplitOptions.None);
By the way: Possible Clone of this answer
Why does "abcd".StartsWith("") return true?
Do you really need to split the string, or are you just trying to get all the individual characters?
If so, then a string is also a IEnumerable<char>, and you also have an indexer.
So, what are you actually trying to do?
And no, you can't call the split methods with string.Empty or similar constructs.
string emptyString = string.Empty;
char[] emptyStringCharArr = emptyString.ToCharArray();
This will give you an empty array of chars.
This is because String is already an array of chars in memory, and String.Empty has no value.
To break it down further, consider an implementation of .ToCharArray()
private Char[] toCharArray(String value)
{
var stringLength = value.Length;
var returningArray = new char[stringLength];
for(var i = 0; i < stringLength; i++)
{
returningArray[i] = value[i];
}
return returningArray;
}
Length of course will be zero, and you will return an empty char array. Of course this isn't the exact implementation, but you can see how and why it's returning nothing (and therefore isn't splitting on the string as you're expecting it to)
It's not an array with a single element String.Empty, because that doesn't really make sense. When you try to split on an empty array, it doesn't know how or what to split on, so you're given back the original string.
As for why it returns 0 by default, consider:
private int IndexOf(String value, String searchFor)
{
for(var i = 0; i < value.Length; i++)
{
if(value.Substring(i, searchFor.Length) == searchFor)
{
return i;
}
}
return -1;
}
private int LastIndexOf(String value, String searchFor)
{
var searchLength = searchFor.Length;
for(var i = value.Length - searchFor.Length; i >= 0; i--)
{
if(value.Substring(i, searchLength) == searchFor)
return i;
}
return -1;
}
String.SubString(x, 0) will ALWAYS return String.Empty, regardless of what's passed in (even String.Empty). For this reason it's much faster to add a check and return 0 regardless (as it would even if it ran the loop).
Since String.Empty is just an empty string, so if you do:
var s = "part1" + string.Empty + "part2";
this will result in exactly the same string as:
var s = "part1" + "part2";
the first syntax will not insert a magic empty string between the two parts.
That IndexOf returns 0, is by definition, not because there is some magic empty string between characters.
I cannot think of a logic way to split a string, by an empty string. What should it return? When using an empty string as an argument to the string.Split method, it will be ignored. If it was the only separator to use, the string will be returned unsplit.
you could also say
"testing" == string.Empty + string.Empty + string.Empty + ... + "t" + string.Empty + string.empty + "esting";
So actually you could place an endless array of string.empty between each character.
So I think
1 not possible
2 none, it just doens't make sense...
I need to search a string and replace all occurrences of %FirstName% and %PolicyAmount% with a value pulled from a database. The problem is the capitalization of FirstName varies. That prevents me from using the String.Replace() method. I've seen web pages on the subject that suggest
Regex.Replace(strInput, strToken, strReplaceWith, RegexOptions.IgnoreCase);
However for some reason when I try and replace %PolicyAmount% with $0, the replacement never takes place. I assume that it has something to do with the dollar sign being a reserved character in regex.
Is there another method I can use that doesn't involve sanitizing the input to deal with regex special characters?
Seems like string.Replace should have an overload that takes a StringComparison argument. Since it doesn't, you could try something like this:
public static string ReplaceString(string str, string oldValue, string newValue, StringComparison comparison)
{
StringBuilder sb = new StringBuilder();
int previousIndex = 0;
int index = str.IndexOf(oldValue, comparison);
while (index != -1)
{
sb.Append(str.Substring(previousIndex, index - previousIndex));
sb.Append(newValue);
index += oldValue.Length;
previousIndex = index;
index = str.IndexOf(oldValue, index, comparison);
}
sb.Append(str.Substring(previousIndex));
return sb.ToString();
}
From MSDN
$0 - "Substitutes the last substring matched by group number number (decimal)."
In .NET Regular expressions group 0 is always the entire match. For a literal $ you need to
string value = Regex.Replace("%PolicyAmount%", "%PolicyAmount%", #"$$0", RegexOptions.IgnoreCase);
Kind of a confusing group of answers, in part because the title of the question is actually much larger than the specific question being asked. After reading through, I'm not sure any answer is a few edits away from assimilating all the good stuff here, so I figured I'd try to sum.
Here's an extension method that I think avoids the pitfalls mentioned here and provides the most broadly applicable solution.
public static string ReplaceCaseInsensitiveFind(this string str, string findMe,
string newValue)
{
return Regex.Replace(str,
Regex.Escape(findMe),
Regex.Replace(newValue, "\\$[0-9]+", #"$$$0"),
RegexOptions.IgnoreCase);
}
So...
This is an extension method #MarkRobinson
This doesn't try to skip Regex #Helge (you really have to do byte-by-byte if you want to string sniff like this outside of Regex)
Passes #MichaelLiu 's excellent test case, "œ".ReplaceCaseInsensitiveFind("oe", ""), though he may have had a slightly different behavior in mind.
Unfortunately, #HA 's comment that you have to Escape all three isn't correct. The initial value and newValue doesn't need to be.
Note: You do, however, have to escape $s in the new value that you're inserting if they're part of what would appear to be a "captured value" marker. Thus the three dollar signs in the Regex.Replace inside the Regex.Replace [sic]. Without that, something like this breaks...
"This is HIS fork, hIs spoon, hissssssss knife.".ReplaceCaseInsensitiveFind("his", #"he$0r")
Here's the error:
An unhandled exception of type 'System.ArgumentException' occurred in System.dll
Additional information: parsing "The\hisr\ is\ he\HISr\ fork,\ he\hIsr\ spoon,\ he\hisrsssssss\ knife\." - Unrecognized escape sequence \h.
Tell you what, I know folks that are comfortable with Regex feel like their use avoids errors, but I'm often still partial to byte sniffing strings (but only after having read Spolsky on encodings) to be absolutely sure you're getting what you intended for important use cases. Reminds me of Crockford on "insecure regular expressions" a little. Too often we write regexps that allow what we want (if we're lucky), but unintentionally allow more in (eg, Is $10 really a valid "capture value" string in my newValue regexp, above?) because we weren't thoughtful enough. Both methods have value, and both encourage different types of unintentional errors. It's often easy to underestimate complexity.
That weird $ escaping (and that Regex.Escape didn't escape captured value patterns like $0 as I would have expected in replacement values) drove me mad for a while. Programming Is Hard (c) 1842
Seems the easiest method is simply to use the Replace method that ships with .Net and has been around since .Net 1.0:
string res = Microsoft.VisualBasic.Strings.Replace(res,
"%PolicyAmount%",
"$0",
Compare: Microsoft.VisualBasic.CompareMethod.Text);
In order to use this method, you have to add a Reference to the Microsoft.VisualBasic assemblly. This assembly is a standard part of the .Net runtime, it is not an extra download or marked as obsolete.
Here's an extension method. Not sure where I found it.
public static class StringExtensions
{
public static string Replace(this string originalString, string oldValue, string newValue, StringComparison comparisonType)
{
int startIndex = 0;
while (true)
{
startIndex = originalString.IndexOf(oldValue, startIndex, comparisonType);
if (startIndex == -1)
break;
originalString = originalString.Substring(0, startIndex) + newValue + originalString.Substring(startIndex + oldValue.Length);
startIndex += newValue.Length;
}
return originalString;
}
}
/// <summary>
/// A case insenstive replace function.
/// </summary>
/// <param name="originalString">The string to examine.(HayStack)</param>
/// <param name="oldValue">The value to replace.(Needle)</param>
/// <param name="newValue">The new value to be inserted</param>
/// <returns>A string</returns>
public static string CaseInsenstiveReplace(string originalString, string oldValue, string newValue)
{
Regex regEx = new Regex(oldValue,
RegexOptions.IgnoreCase | RegexOptions.Multiline);
return regEx.Replace(originalString, newValue);
}
Inspired by cfeduke's answer, I made this function which uses IndexOf to find the old value in the string and then replaces it with the new value. I used this in an SSIS script processing millions of rows, and the regex-method was way slower than this.
public static string ReplaceCaseInsensitive(this string str, string oldValue, string newValue)
{
int prevPos = 0;
string retval = str;
// find the first occurence of oldValue
int pos = retval.IndexOf(oldValue, StringComparison.InvariantCultureIgnoreCase);
while (pos > -1)
{
// remove oldValue from the string
retval = retval.Remove(pos, oldValue.Length);
// insert newValue in it's place
retval = retval.Insert(pos, newValue);
// check if oldValue is found further down
prevPos = pos + newValue.Length;
pos = retval.IndexOf(oldValue, prevPos, StringComparison.InvariantCultureIgnoreCase);
}
return retval;
}
Expanding on C. Dragon 76's popular answer by making his code into an extension that overloads the default Replace method.
public static class StringExtensions
{
public static string Replace(this string str, string oldValue, string newValue, StringComparison comparison)
{
StringBuilder sb = new StringBuilder();
int previousIndex = 0;
int index = str.IndexOf(oldValue, comparison);
while (index != -1)
{
sb.Append(str.Substring(previousIndex, index - previousIndex));
sb.Append(newValue);
index += oldValue.Length;
previousIndex = index;
index = str.IndexOf(oldValue, index, comparison);
}
sb.Append(str.Substring(previousIndex));
return sb.ToString();
}
}
Since .NET Core 2.0 or .NET Standard 2.1 respectively, this is baked into the .NET runtime [1]:
"hello world".Replace("World", "csharp", StringComparison.CurrentCultureIgnoreCase); // "hello csharp"
[1] https://learn.microsoft.com/en-us/dotnet/api/system.string.replace#System_String_Replace_System_String_System_String_System_StringComparison_
Based on Jeff Reddy's answer, with some optimisations and validations:
public static string Replace(string str, string oldValue, string newValue, StringComparison comparison)
{
if (oldValue == null)
throw new ArgumentNullException("oldValue");
if (oldValue.Length == 0)
throw new ArgumentException("String cannot be of zero length.", "oldValue");
StringBuilder sb = null;
int startIndex = 0;
int foundIndex = str.IndexOf(oldValue, comparison);
while (foundIndex != -1)
{
if (sb == null)
sb = new StringBuilder(str.Length + (newValue != null ? Math.Max(0, 5 * (newValue.Length - oldValue.Length)) : 0));
sb.Append(str, startIndex, foundIndex - startIndex);
sb.Append(newValue);
startIndex = foundIndex + oldValue.Length;
foundIndex = str.IndexOf(oldValue, startIndex, comparison);
}
if (startIndex == 0)
return str;
sb.Append(str, startIndex, str.Length - startIndex);
return sb.ToString();
}
a version similar to C. Dragon's, but for if you only need a single replacement:
int n = myText.IndexOf(oldValue, System.StringComparison.InvariantCultureIgnoreCase);
if (n >= 0)
{
myText = myText.Substring(0, n)
+ newValue
+ myText.Substring(n + oldValue.Length);
}
Here is another option for executing Regex replacements, since not many people seem to notice the matches contain the location within the string:
public static string ReplaceCaseInsensative( this string s, string oldValue, string newValue ) {
var sb = new StringBuilder(s);
int offset = oldValue.Length - newValue.Length;
int matchNo = 0;
foreach (Match match in Regex.Matches(s, Regex.Escape(oldValue), RegexOptions.IgnoreCase))
{
sb.Remove(match.Index - (offset * matchNo), match.Length).Insert(match.Index - (offset * matchNo), newValue);
matchNo++;
}
return sb.ToString();
}
Let me make my case and then you can tear me to shreds if you like.
Regex is not the answer for this problem - too slow and memory hungry, relatively speaking.
StringBuilder is much better than string mangling.
Since this will be an extension method to supplement string.Replace, I believe it important to match how that works - therefore throwing exceptions for the same argument issues is important as is returning the original string if a replacement was not made.
I believe that having a StringComparison parameter is not a good idea.
I did try it but the test case originally mentioned by michael-liu showed a problem:-
[TestCase("œ", "oe", "", StringComparison.InvariantCultureIgnoreCase, Result = "")]
Whilst IndexOf will match, there is a mismatch between the length of the match in the source string (1) and oldValue.Length (2). This manifested itself by causing IndexOutOfRange in some other solutions when oldValue.Length was added to the current match position and I could not find a way around this.
Regex fails to match the case anyway, so I took the pragmatic solution of only using StringComparison.OrdinalIgnoreCase for my solution.
My code is similar to other answers but my twist is that I look for a match before going to the trouble of creating a StringBuilder. If none is found then a potentially large allocation is avoided. The code then becomes a do{...}while rather than a while{...}
I have done some extensive testing against other Answers and this came out fractionally faster and used slightly less memory.
public static string ReplaceCaseInsensitive(this string str, string oldValue, string newValue)
{
if (str == null) throw new ArgumentNullException(nameof(str));
if (oldValue == null) throw new ArgumentNullException(nameof(oldValue));
if (oldValue.Length == 0) throw new ArgumentException("String cannot be of zero length.", nameof(oldValue));
var position = str.IndexOf(oldValue, 0, StringComparison.OrdinalIgnoreCase);
if (position == -1) return str;
var sb = new StringBuilder(str.Length);
var lastPosition = 0;
do
{
sb.Append(str, lastPosition, position - lastPosition);
sb.Append(newValue);
} while ((position = str.IndexOf(oldValue, lastPosition = position + oldValue.Length, StringComparison.OrdinalIgnoreCase)) != -1);
sb.Append(str, lastPosition, str.Length - lastPosition);
return sb.ToString();
}
Regex.Replace(strInput, strToken.Replace("$", "[$]"), strReplaceWith, RegexOptions.IgnoreCase);
The regular expression method should work. However what you can also do is lower case the string from the database, lower case the %variables% you have, and then locate the positions and lengths in the lower cased string from the database. Remember, positions in a string don't change just because its lower cased.
Then using a loop that goes in reverse (its easier, if you do not you will have to keep a running count of where later points move to) remove from your non-lower cased string from the database the %variables% by their position and length and insert the replacement values.
(Since everyone is taking a shot at this). Here's my version (with null checks, and correct input and replacement escaping) ** Inspired from around the internet and other versions:
using System;
using System.Text.RegularExpressions;
public static class MyExtensions {
public static string ReplaceIgnoreCase(this string search, string find, string replace) {
return Regex.Replace(search ?? "", Regex.Escape(find ?? ""), (replace ?? "").Replace("$", "$$"), RegexOptions.IgnoreCase);
}
}
Usage:
var result = "This is a test".ReplaceIgnoreCase("IS", "was");