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How do convert a string to lowercase except for the first character?
Can this be completed with LINQ?
Thanks
If you only have one word in the string, you can use TextInfo.ToTitleCase. No need to use Linq.
As #Guffa noted:
This will convert any string to title case, so, "hello world" and "HELLO WORLD" would both be converted to "Hello World".
To achieve exectly what you asked (convert all characters to lower, except the first one), you can do the following:
string mostLower = myString.Substring(0, 1) + myString.Substring(1).ToLower();
This can be done with simple string operations:
s = s.Substring(0, 1) + s.Substring(1).ToLower();
Note that this does exactly what you asked for, i.e. it converts all characters to lower case except the first one that is left unchanged.
If you instead also want to change the first character to upper case, you would do:
s = s.Substring(0, 1).ToUpper() + s.Substring(1).ToLower();
Note that this code assumes that there is at least two characters in the strings. If there is a possibility that it's shorter, you should of course test for that first.
String newString = new String(str.Select((ch, index) => (index == 0) ? ch : Char.ToLower(ch)).ToArray());
Use namespace: using System.Globalization;
...
string value = CultureInfo.CurrentCulture.TextInfo.ToTitleCase("hello");
EDIT
This code work only if its single word .For convert all character into lower except first letter check Guffa Answer.
string value = myString.Substring(0, 1) + myString.Substring(1).ToLower();
Not sure you can do it in linq here is a non-linq approach:
public static string FirstCap(string value)
{
string result = String.Empty;
if(!String.IsNullOrEmpty(value))
{
if(value.Length == 1)
{
result = value.ToUpper();
}
else
{
result = value.Substring(0,1).ToString().ToUpper() + value.Substring(1).ToLower();
}
}
return result;
}
based on guffa's example above (slightly amended). you could convert that to an extension method (please pardon the badly named method :)):
public static string UpperFirst(this string source)
{
return source.ToLower().Remove(0, 1)
.Insert(0, source.Substring(0, 1).ToUpper());
}
usage:
var myNewString = myOldString.UpperFirst();
// or simply referenced as myOldString.UpperFirst() where required
cheers guffa
var initialString = "Hello hOW r u?";
var res = string.Concat(initialString..ToUpper().Substring(0, 1), initialString.ToLower().Substring(1));
You can use an extension method:
static class StringExtensions
{
public static string ToLowerFirst(this string text)
=> !string.IsNullOrEmpty(text)
? $"{text.Substring(0, 1).ToLower()}{text.Substring(1)}"
: text;
}
Unit tests as well (using FluentAssertions and Microsoft UnitTesting):
[TestClass]
public class StringExtensionsTests
{
[TestMethod]
public void ToLowerFirst_ShouldReturnCorrectValue()
=> "ABCD"
.ToLowerFirst()
.Should()
.Be("aBCD");
[TestMethod]
public void ToLowerFirst_WhenStringIsEmpty_ShouldReturnCorrectValue()
=> string.Empty
.ToLowerFirst()
.Should()
.Be(string.Empty);
}
I have a string say
"Hello! world!"
I want to do a trim or a remove to take out the ! off world but not off Hello.
"Hello! world!".TrimEnd('!');
read more
EDIT:
What I've noticed in this type of questions that quite everyone suggest to remove the last char of given string. But this does not fulfill the definition of Trim method.
Trim - Removes all occurrences of
white space characters from the
beginning and end of this instance.
MSDN-Trim
Under this definition removing only last character from string is bad solution.
So if we want to "Trim last character from string" we should do something like this
Example as extension method:
public static class MyExtensions
{
public static string TrimLastCharacter(this String str)
{
if(String.IsNullOrEmpty(str)){
return str;
} else {
return str.TrimEnd(str[str.Length - 1]);
}
}
}
Note if you want to remove all characters of the same value i.e(!!!!)the method above removes all existences of '!' from the end of the string,
but if you want to remove only the last character you should use this :
else { return str.Remove(str.Length - 1); }
String withoutLast = yourString.Substring(0,(yourString.Length - 1));
if (yourString.Length > 1)
withoutLast = yourString.Substring(0, yourString.Length - 1);
or
if (yourString.Length > 1)
withoutLast = yourString.TrimEnd().Substring(0, yourString.Length - 1);
...in case you want to remove a non-whitespace character from the end.
The another example of trimming last character from a string:
string outputText = inputText.Remove(inputText.Length - 1, 1);
You can put it into an extension method and prevent it from null string, etc.
Try this:
return( (str).Remove(str.Length-1) );
In .NET 5 / C# 8:
You can write the code marked as the answer as:
public static class StringExtensions
{
public static string TrimLastCharacters(this string str) => string.IsNullOrEmpty(str) ? str : str.TrimEnd(str[^1]);
}
However, as mentioned in the answer, this removes all occurrences of that last character. If you only want to remove the last character you should instead do:
public static string RemoveLastCharacter(this string str) => string.IsNullOrEmpty(str) ? str : str[..^1];
A quick explanation for the new stuff in C# 8:
The ^ is called the "index from end operator". The .. is called the "range operator". ^1 is a shortcut for arr.length - 1. You can get all items after the first character of an array with arr[1..] or all items before the last with arr[..^1]. These are just a few quick examples. For more information, see https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8, "Indices and ranges" section.
string s1 = "Hello! world!";
string s2 = s1.Trim('!');
string helloOriginal = "Hello! World!";
string newString = helloOriginal.Substring(0,helloOriginal.LastIndexOf('!'));
string s1 = "Hello! world!"
string s2 = s1.Substring(0, s1.Length - 1);
Console.WriteLine(s1);
Console.WriteLine(s2);
Very easy and simple:
str = str.Remove( str.Length - 1 );
you could also use this:
public static class Extensions
{
public static string RemovePrefix(this string o, string prefix)
{
if (prefix == null) return o;
return !o.StartsWith(prefix) ? o : o.Remove(0, prefix.Length);
}
public static string RemoveSuffix(this string o, string suffix)
{
if(suffix == null) return o;
return !o.EndsWith(suffix) ? o : o.Remove(o.Length - suffix.Length, suffix.Length);
}
}
An example Extension class to simplify this: -
internal static class String
{
public static string TrimEndsCharacter(this string target, char character) => target?.TrimLeadingCharacter(character).TrimTrailingCharacter(character);
public static string TrimLeadingCharacter(this string target, char character) => Match(target?.Substring(0, 1), character) ? target.Remove(0,1) : target;
public static string TrimTrailingCharacter(this string target, char character) => Match(target?.Substring(target.Length - 1, 1), character) ? target.Substring(0, target.Length - 1) : target;
private static bool Match(string value, char character) => !string.IsNullOrEmpty(value) && value[0] == character;
}
Usage
"!Something!".TrimLeadingCharacter('X'); // Result '!Something!' (No Change)
"!Something!".TrimTrailingCharacter('S'); // Result '!Something!' (No Change)
"!Something!".TrimEndsCharacter('g'); // Result '!Something!' (No Change)
"!Something!".TrimLeadingCharacter('!'); // Result 'Something!' (1st Character removed)
"!Something!".TrimTrailingCharacter('!'); // Result '!Something' (Last Character removed)
"!Something!".TrimEndsCharacter('!'); // Result 'Something' (End Characters removed)
"!!Something!!".TrimLeadingCharacter('!'); // Result '!Something!!' (Only 1st instance removed)
"!!Something!!".TrimTrailingCharacter('!'); // Result '!!Something!' (Only Last instance removed)
"!!Something!!".TrimEndsCharacter('!'); // Result '!Something!' (Only End instances removed)
Slightly modified version of #Damian Leszczyński - Vash that will make sure that only a specific character will be removed.
public static class StringExtensions
{
public static string TrimLastCharacter(this string str, char character)
{
if (string.IsNullOrEmpty(str) || str[str.Length - 1] != character)
{
return str;
}
return str.Substring(0, str.Length - 1);
}
}
I took the path of writing an extension using the TrimEnd just because I was already using it inline and was happy with it...
i.e.:
static class Extensions
{
public static string RemoveLastChars(this String text, string suffix)
{
char[] trailingChars = suffix.ToCharArray();
if (suffix == null) return text;
return text.TrimEnd(trailingChars);
}
}
Make sure you include the namespace in your classes using the static class ;P and usage is:
string _ManagedLocationsOLAP = string.Empty;
_ManagedLocationsOLAP = _validManagedLocationIDs.RemoveLastChars(",");
If you want to remove the '!' character from a specific expression("world" in your case), then you can use this regular expression
string input = "Hello! world!";
string output = Regex.Replace(input, "(world)!", "$1", RegexOptions.Multiline | RegexOptions.Singleline);
// result: "Hello! world"
the $1 special character contains all the matching "world" expressions, and it is used to replace the original "world!" expression
I'd like to have a method that transforms the first character of a string into lower case.
My approaches:
1.
public static string ReplaceFirstCharacterToLowerVariant(string name)
{
return String.Format("{0}{1}", name.First().ToString().ToLowerInvariant(), name.Substring(1));
}
2.
public static IEnumerable<char> FirstLetterToLowerCase(string value)
{
var firstChar = (byte)value.First();
return string.Format("{0}{1}", (char)(firstChar + 32), value.Substring(1));
}
What would be your approach?
I would use simple concatenation:
Char.ToLowerInvariant(name[0]) + name.Substring(1)
The first solution is not optimized because string.Format is slow and you don't need it if you have a format that will never change. It also generates an extra string to covert the letter to lowercase, which is not needed.
The approach with "+ 32" is ugly / not maintainable as it requires knowledge of ASCII character value offsets. It will also generate incorrect output with Unicode data and ASCII symbol characters.
Depending on the situation, a little defensive programming might be desirable:
public static string FirstCharacterToLower(string str)
{
if (String.IsNullOrEmpty(str) || Char.IsLower(str, 0))
return str;
return Char.ToLowerInvariant(str[0]) + str.Substring(1);
}
The if statement also prevents a new string from being built if it's not going to be changed anyway. You might want to have the method fail on null input instead, and throw an ArgumentNullException.
As people have mentioned, using String.Format for this is overkill.
Just in case it helps anybody who happens to stumble across this answer.
I think this would be best as an extension method, then you can call it with yourString.FirstCharacterToLower();
public static class StringExtensions
{
public static string FirstCharacterToLower(this string str)
{
if (String.IsNullOrEmpty(str) || Char.IsLower(str, 0))
{
return str;
}
return Char.ToLowerInvariant(str[0]) + str.Substring(1);
}
}
The fastest solution I know without abusing c#:
public static string LowerCaseFirstLetter(string value)
{
if (value?.Length > 0)
{
var letters = value.ToCharArray();
letters[0] = char.ToLowerInvariant(letters[0]);
return new string(letters);
}
return value;
}
Mine is
if (!string.IsNullOrEmpty (val) && val.Length > 0)
{
return val[0].ToString().ToLowerInvariant() + val.Remove (0,1);
}
I like the accepted answer, but beside checking string.IsNullOrEmpty I would also check if Char.IsLower(name[1]) in case you are dealing with abbreviation. E.g. you would not want "AIDS" to become "aIDS".
If you care about performance I would go with
public static string FirstCharToLower(this string str)
=> string.Create(str.Length, str, (output, input) =>
{
input.CopyTo(output);
output[0] = char.ToLowerInvariant(input[0]);
});
I did some quick benchmarking and it seems to be at least twice as fast as the fastest solution posted here and 3.5 times faster than the worst one across multiple input lengths.
There is no input checking as it should be the responsibility of the caller. Allowing you to prepare your data in advance and do fast bulk processing not being slowed down by having branches in your hot path if you ever need it.
With range operator C# 8.0 or above you can do this:
Char.ToLowerInvariant(name[0]) + name[1..];
Combined a few and made it a chainable extension. Added short-circuit on whitespace and non-letter.
public static string FirstLower(this string input) =>
(!string.IsNullOrWhiteSpace(input) && input.Length > 0
&& char.IsLetter(input[0]) && !char.IsLower(input[0]))
? input[0].ToString().ToLowerInvariant() + input.Remove(0, 1) : input;
This is a little extension method using latest syntax and correct validations
public static class StringExtensions
{
public static string FirstCharToLower(this string input)
{
switch (input)
{
case null: throw new ArgumentNullException(nameof(input));
case "": throw new ArgumentException($"{nameof(input)} cannot be empty", nameof(input));
default: return input.First().ToString().ToLower() + input.Substring(1);
}
}
}
Use This:
string newName= name[0].ToString().ToLower() + name.Substring(1);
If you don't want to reference your string twice in your expression you could do this using System.Linq.
new string("Hello World".Select((c, i) => i == 0 ? char.ToLower(c) : c).ToArray())
That way if your string comes from a function, you don't have to store the result of that function.
new string(Console.ReadLine().Select((c, i) => i == 0 ? char.ToLower(c) : c).ToArray())
It is better to use String.Concat than String.Format if you know that format is not change data, and just concatenation is desired.
What is needed to make String.IsNullOrEmpty() count whitespace strings as empty?
Eg. I want the following to return true instead of the usual false:
String.IsNullOrEmpty(" ");
Is there a better approach than:
String.IsNullOrEmpty(" ".Trim());
(Note that the original question asked what the return would be normally hence the unsympathetic comments, this has been replaced with a more sensible question).
.NET 4.0 will introduce the method String.IsNullOrWhiteSpace. Until then you'll need to use Trim if you want to deal with white space strings the same way you deal with empty strings.
For code not using .NET 4.0, a helper method to check for null or empty or whitespace strings can be implemented like this:
public static bool IsNullOrWhiteSpace(string value)
{
if (String.IsNullOrEmpty(value))
{
return true;
}
return String.IsNullOrEmpty(value.Trim());
}
The String.IsNullOrEmpty will not perform any trimming and will just check if the string is a null reference or an empty string.
String.IsNullOrEmpty(" ")
...Returns False
String foo = null;
String.IsNullOrEmpty( foo.Trim())
...Throws an exception as foo is Null.
String.IsNullOrEmpty( foo ) || foo.Trim() == String.Empty
...Returns true
Of course, you could implement it as an extension function:
static class StringExtensions
{
public static bool IsNullOrWhiteSpace(this string value)
{
return (String.IsNullOrEmpty(value) || String.IsNullOrEmpty(value.Trim()));
}
}
My program will take arbitrary strings from the internet and use them for file names. Is there a simple way to remove the bad characters from these strings or do I need to write a custom function for this?
Ugh, I hate it when people try to guess at which characters are valid. Besides being completely non-portable (always thinking about Mono), both of the earlier comments missed more 25 invalid characters.
foreach (var c in Path.GetInvalidFileNameChars())
{
fileName = fileName.Replace(c, '-');
}
Or in VB:
'Clean just a filename
Dim filename As String = "salmnas dlajhdla kjha;dmas'lkasn"
For Each c In IO.Path.GetInvalidFileNameChars
filename = filename.Replace(c, "")
Next
'See also IO.Path.GetInvalidPathChars
To strip invalid characters:
static readonly char[] invalidFileNameChars = Path.GetInvalidFileNameChars();
// Builds a string out of valid chars
var validFilename = new string(filename.Where(ch => !invalidFileNameChars.Contains(ch)).ToArray());
To replace invalid characters:
static readonly char[] invalidFileNameChars = Path.GetInvalidFileNameChars();
// Builds a string out of valid chars and an _ for invalid ones
var validFilename = new string(filename.Select(ch => invalidFileNameChars.Contains(ch) ? '_' : ch).ToArray());
To replace invalid characters (and avoid potential name conflict like Hell* vs Hell$):
static readonly IList<char> invalidFileNameChars = Path.GetInvalidFileNameChars();
// Builds a string out of valid chars and replaces invalid chars with a unique letter (Moves the Char into the letter range of unicode, starting at "A")
var validFilename = new string(filename.Select(ch => invalidFileNameChars.Contains(ch) ? Convert.ToChar(invalidFileNameChars.IndexOf(ch) + 65) : ch).ToArray());
This question has been asked many times before and, as pointed out many times before, IO.Path.GetInvalidFileNameChars is not adequate.
First, there are many names like PRN and CON that are reserved and not allowed for filenames. There are other names not allowed only at the root folder. Names that end in a period are also not allowed.
Second, there are a variety of length limitations. Read the full list for NTFS here.
Third, you can attach to filesystems that have other limitations. For example, ISO 9660 filenames cannot start with "-" but can contain it.
Fourth, what do you do if two processes "arbitrarily" pick the same name?
In general, using externally-generated names for file names is a bad idea. I suggest generating your own private file names and storing human-readable names internally.
I agree with Grauenwolf and would highly recommend the Path.GetInvalidFileNameChars()
Here's my C# contribution:
string file = #"38?/.\}[+=n a882 a.a*/|n^%$ ad#(-))";
Array.ForEach(Path.GetInvalidFileNameChars(),
c => file = file.Replace(c.ToString(), String.Empty));
p.s. -- this is more cryptic than it should be -- I was trying to be concise.
Here's my version:
static string GetSafeFileName(string name, char replace = '_') {
char[] invalids = Path.GetInvalidFileNameChars();
return new string(name.Select(c => invalids.Contains(c) ? replace : c).ToArray());
}
I'm not sure how the result of GetInvalidFileNameChars is calculated, but the "Get" suggests it's non-trivial, so I cache the results. Further, this only traverses the input string once instead of multiple times, like the solutions above that iterate over the set of invalid chars, replacing them in the source string one at a time. Also, I like the Where-based solutions, but I prefer to replace invalid chars instead of removing them. Finally, my replacement is exactly one character to avoid converting characters to strings as I iterate over the string.
I say all that w/o doing the profiling -- this one just "felt" nice to me. : )
Here's the function that I am using now (thanks jcollum for the C# example):
public static string MakeSafeFilename(string filename, char replaceChar)
{
foreach (char c in System.IO.Path.GetInvalidFileNameChars())
{
filename = filename.Replace(c, replaceChar);
}
return filename;
}
I just put this in a "Helpers" class for convenience.
If you want to quickly strip out all special characters which is sometimes more user readable for file names this works nicely:
string myCrazyName = "q`w^e!r#t#y$u%i^o&p*a(s)d_f-g+h=j{k}l|z:x\"c<v>b?n[m]q\\w;e'r,t.y/u";
string safeName = Regex.Replace(
myCrazyName,
"\W", /*Matches any nonword character. Equivalent to '[^A-Za-z0-9_]'*/
"",
RegexOptions.IgnoreCase);
// safeName == "qwertyuiopasd_fghjklzxcvbnmqwertyu"
Here's what I just added to ClipFlair's (http://github.com/Zoomicon/ClipFlair) StringExtensions static class (Utils.Silverlight project), based on info gathered from the links to related stackoverflow questions posted by Dour High Arch above:
public static string ReplaceInvalidFileNameChars(this string s, string replacement = "")
{
return Regex.Replace(s,
"[" + Regex.Escape(new String(System.IO.Path.GetInvalidPathChars())) + "]",
replacement, //can even use a replacement string of any length
RegexOptions.IgnoreCase);
//not using System.IO.Path.InvalidPathChars (deprecated insecure API)
}
static class Utils
{
public static string MakeFileSystemSafe(this string s)
{
return new string(s.Where(IsFileSystemSafe).ToArray());
}
public static bool IsFileSystemSafe(char c)
{
return !Path.GetInvalidFileNameChars().Contains(c);
}
}
Why not convert the string to a Base64 equivalent like this:
string UnsafeFileName = "salmnas dlajhdla kjha;dmas'lkasn";
string SafeFileName = Convert.ToBase64String(Encoding.UTF8.GetBytes(UnsafeFileName));
If you want to convert it back so you can read it:
UnsafeFileName = Encoding.UTF8.GetString(Convert.FromBase64String(SafeFileName));
I used this to save PNG files with a unique name from a random description.
private void textBoxFileName_KeyPress(object sender, KeyPressEventArgs e)
{
e.Handled = CheckFileNameSafeCharacters(e);
}
/// <summary>
/// This is a good function for making sure that a user who is naming a file uses proper characters
/// </summary>
/// <param name="e"></param>
/// <returns></returns>
internal static bool CheckFileNameSafeCharacters(System.Windows.Forms.KeyPressEventArgs e)
{
if (e.KeyChar.Equals(24) ||
e.KeyChar.Equals(3) ||
e.KeyChar.Equals(22) ||
e.KeyChar.Equals(26) ||
e.KeyChar.Equals(25))//Control-X, C, V, Z and Y
return false;
if (e.KeyChar.Equals('\b'))//backspace
return false;
char[] charArray = Path.GetInvalidFileNameChars();
if (charArray.Contains(e.KeyChar))
return true;//Stop the character from being entered into the control since it is non-numerical
else
return false;
}
From my older projects, I've found this solution, which has been working perfectly over 2 years. I'm replacing illegal chars with "!", and then check for double !!'s, use your own char.
public string GetSafeFilename(string filename)
{
string res = string.Join("!", filename.Split(Path.GetInvalidFileNameChars()));
while (res.IndexOf("!!") >= 0)
res = res.Replace("!!", "!");
return res;
}
I find using this to be quick and easy to understand:
<Extension()>
Public Function MakeSafeFileName(FileName As String) As String
Return FileName.Where(Function(x) Not IO.Path.GetInvalidFileNameChars.Contains(x)).ToArray
End Function
This works because a string is IEnumerable as a char array and there is a string constructor string that takes a char array.
Many anwer suggest to use Path.GetInvalidFileNameChars() which seems like a bad solution to me. I encourage you to use whitelisting instead of blacklisting because hackers will always find a way eventually to bypass it.
Here is an example of code you could use :
string whitelist = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ.";
foreach (char c in filename)
{
if (!whitelist.Contains(c))
{
filename = filename.Replace(c, '-');
}
}