Most efficient way to remove special characters from string
Why do you think that your method is not efficient? It's actually one of the most efficient ways that you can do it.
You should of course read the character into a local variable or use an enumerator to reduce the number of array accesses:
public static string RemoveSpecialCharacters(this string str) {
StringBuilder sb = new StringBuilder();
foreach (char c in str) {
if ((c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || c == '.' || c == '_') {
sb.Append(c);
}
}
return sb.ToString();
}
One thing that makes a method like this efficient is that it scales well. The execution time will be relative to the length of the string. There is no nasty surprises if you would use it on a large string.
Edit:
I made a quick performance test, running each function a million times with a 24 character string. These are the results:
Original function: 54.5 ms.
My suggested change: 47.1 ms.
Mine with setting StringBuilder capacity: 43.3 ms.
Regular expression: 294.4 ms.
Edit 2:
I added the distinction between A-Z and a-z in the code above. (I reran the performance test, and there is no noticable difference.)
Edit 3:
I tested the lookup+char[] solution, and it runs in about 13 ms.
The price to pay is, of course, the initialization of the huge lookup table and keeping it in memory. Well, it's not that much data, but it's much for such a trivial function...
private static bool[] _lookup;
static Program() {
_lookup = new bool[65536];
for (char c = '0'; c <= '9'; c++) _lookup[c] = true;
for (char c = 'A'; c <= 'Z'; c++) _lookup[c] = true;
for (char c = 'a'; c <= 'z'; c++) _lookup[c] = true;
_lookup['.'] = true;
_lookup['_'] = true;
}
public static string RemoveSpecialCharacters(string str) {
char[] buffer = new char[str.Length];
int index = 0;
foreach (char c in str) {
if (_lookup[c]) {
buffer[index] = c;
index++;
}
}
return new string(buffer, 0, index);
}
Fastest way to remove the leading special characters in string in c#
You could use string.TrimStart and pass in the characters you want to remove:
var result = yourString.TrimStart('-', '_');
However, this is only a good idea if the number of special characters you want to remove is well-known and small.
If that's not the case, you can use regular expressions:
var result = Regex.Replace(yourString, "^[^A-Za-z0-9]*", "");
How to remove special characters at the Beginning and End of the string and not for numeric?
In order to reproduce your issue, I created this class containing your initial attempt to solve the problem - I've refactored it a bit and renamed some of the variables, but I believe this is functionally identical to the code in your question.
namespace StackOverflow69116104SpecialChars
{
using System;
using System.Collections.Generic;
using System.Linq;
public class Cleaner
{
private readonly string[] specialCharacters = { "#", "$", ",", "/", "!", "@", "^", "&", "*", "(", ")", "'", "\"", ";", "_", ":", "|", "[", "]" };
public string[] Original(string[] words)
{
var cleaned = new List<string>();
foreach (string word in words)
{
var split = word.Split(specialCharacters, StringSplitOptions.RemoveEmptyEntries);
if (!string.IsNullOrWhiteSpace(split.FirstOrDefault()))
{
cleaned.Add(string.Join(word, split));
}
}
return cleaned.ToArray();
}
}
}
Next step, I created a unit test using your inputs and expected outputs. I've used the Xunit testing framework, but you could do the same using any unit testing framework for .net.
namespace StackOverflow69116104SpecialChars
{
using System.Text;
using Xunit;
public class UnitTest1
{
[Fact]
public void Test1()
{
// Arrange
var uncleanWords = new string[]
{
"#(Super-Good)",
"22\"",
"#50",
"2.20GHz,",
"[Personal})]",
"$44.00",
"55\"",
};
var expectedCleanedWords = new string[]
{
"Super-Good",
"22\"",
"#50",
"2.20GHz",
"Personal",
"$44.00",
"55\"",
};
// Act
var cleaner = new Cleaner();
var actualCleanedWords = cleaner.Original(uncleanWords);
// Assert
Assert.Equal(expectedCleanedWords.Length, actualCleanedWords.Length);
var sb = new StringBuilder();
for (var i = 0; i < expectedCleanedWords.Length; i++)
{
if (expectedCleanedWords[i] != actualCleanedWords[i])
{
sb.AppendLine($"At index {i} expected '{expectedCleanedWords[i]}' but was '{actualCleanedWords[i]}'.");
}
}
if (sb.Length > 0)
{
throw new Xunit.Sdk.XunitException(sb.ToString());
}
}
}
}
This fails with the message
At index 1 expected '22"' but was '22'.
At index 2 expected '#50' but was '50'.
At index 4 expected 'Personal' but was 'Personal}'.
At index 5 expected '$44.00' but was '44.00'.
At index 6 expected '55"' but was '55'.
The first failure, expected '22"' but was '22' is happening because there's no code to meet this requirement:
If a numeric value has any special character then that should be ignored. (i.e., #55 & $55.00 should remain as it is.)
There's no test for whether the string, minus the special characters, is a numeric value (which I'm going to interpret as consisting of the characters 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 or .), so let's try implementing that in a new method called Revision1, with the help of a new private method called IsNumeric.
public string[] Revision1(string[] words)
{
var cleaned = new List<string>();
foreach (string word in words)
{
var split = word.Split(specialCharacters, StringSplitOptions.RemoveEmptyEntries);
var rejoined = string.Join(word, split);
if (IsNumeric(rejoined))
{
// It's a numeric, so return it with its special characters
cleaned.Add(word);
}
else if (!string.IsNullOrWhiteSpace(split.FirstOrDefault()))
{
cleaned.Add(rejoined);
}
}
return cleaned.ToArray();
}
private static bool IsNumeric(string mightBeNumeric)
{
var r = new Regex(@"^[0-9\.]+$");
var match = r.Match(mightBeNumeric);
return match.Success;
}
And update the unit test to call this method instead of the original method:
// Act
var cleaner = new Cleaner();
var actualCleanedWords = cleaner.Revision1(uncleanWords);
The unit test still fails, but in a better way - only one failure now:
At index 4 expected 'Personal' but was 'Personal}'.
The failure at index 4 is pretty easy to fix - you've omitted } (and probably {) from your definition of special characters. Just change specialCharacters to
private readonly string[] specialCharacters = { "#", "$", ",", "/", "!", "@", "^", "&", "*", "(", ")", "'", "\"", ";", "_", ":", "|", "[", "]", "{", "}" };
Now the unit test passes.
Update 18th Sep
After I posted the original answer, @Ask_SO commented
In your code, I do not see logic to remove at the Beginning and End of the string. With this code, it removes special characters from entire string.
So I added another test case - abc#def, which should stay unchanged. Rather surprisingly, it came out as abcabc#defdef.
Looking more closely at the test cases, I noticed that there weren't any to cover a string with special characters at the start and end (which should be removed) and also in the middle (which shouldn't be removed). So I added these to the unit test, along with an empty string (just because that might prove to be problematic).
var uncleanWords = new string[]
{
"abc#def",
"$,abc#@def{}",
"_^abc#def@ghi,,",
"",
"#(Super-Good)",
"22\"",
"#50",
"2.20GHz,",
"[Personal})]",
"$44.00",
"55\"",
};
var expectedCleanedWords = new string[]
{
"abc#def",
"abc#@def",
"abc#def@ghi",
"",
"Super-Good",
"22\"",
"#50",
"2.20GHz",
"Personal",
"$44.00",
"55\"",
};
The unit test now fails on the new test cases, so I came up with a new implementation in a method called Revision2.
public string[] Revision2(string[] words)
{
var cleaned = new List<string>();
foreach (var word in words)
{
var split = word.Split(specialCharacters, StringSplitOptions.RemoveEmptyEntries);
var isNumeric = true;
foreach (var bit in split)
{
if (!IsNumeric(bit))
{
// Part of the string is neither numeric nor a special character
// so we will need to remove special characters from the start
// and end.
isNumeric = false;
break;
}
}
if (isNumeric)
{
// return the whole string unchanged
cleaned.Add(word);
}
else
{
// we need to remove special characters from the start and end
int firstNonSpecialCharacterPosition = 0;
for (var i = 0; i < word.Length; i++)
{
if (!this.specialCharacters.Contains(word[i]))
{
firstNonSpecialCharacterPosition = i;
break;
}
}
int lastNonSpecialCharacterPosition = word.Length;
for (var i = word.Length - 1; i > 0; i--)
{
if (!this.specialCharacters.Contains(word[i]))
{
lastNonSpecialCharacterPosition = i;
break;
}
}
var lengthToKeep = (lastNonSpecialCharacterPosition - firstNonSpecialCharacterPosition) + 1;
var newWord = word.Substring(firstNonSpecialCharacterPosition, lengthToKeep);
cleaned.Add(newWord);
}
}
return cleaned.ToArray();
}
This implementation passes the updated unit test. This is one of the reasons unit tests are important - when following a test-driven development approach, they provide an unambiguous definition of the expected behaviour of the code.
How can I remove extra spaces, special characters, and make string lowercase?
I would argue that trying to combine both patterns into one would make it less readable. You could keep using two calls to Regex.Replace() and just append .ToLower() to the second one:
// Remove special characters except for space and /
str1 = Regex.Replace(str1, @"[^0-9a-zA-Z /]+", "");
// Remove all but one space, trim the ends, and convert to lower case.
str1 = Regex.Replace(str1.Trim(), @"\s+", " ").ToLower();
// ^^^^^^^^^
That said, if you really have to use a one-liner, you could write something like this:
str1 = Regex.Replace(str1, @"[^A-Za-z0-9 /]+|( )+", "$1").Trim().ToLower();
This matches any character not present in the negated character class or one or more space characters, placing the space character in a capturing group, and replaces each match with what was captured in group 1 (i.e., nothing or a single space character).
For the sake of completeness, if you want to also handle the trimming with regex (and make the pattern even less readable), you could:
str1 = Regex.Replace(str1, @"[^A-Za-z0-9 /]+|^ +| +$|( )+", "$1").ToLower();
Removing special characters and spaces from strings
We can use sub to remove the and string, then with gsub remove everything other (^) than the letters (upper, lower case) and convert the case to upper (toupper)
f1 <- function(x) toupper(gsub("[^A-Za-z]", "", sub("and", "", x, fixed = TRUE)))
-testing
> f1(name1)
[1] "ADAMEVE"
> f1(name2)
[1] "SPARTACUS"
> f1(name3)
[1] "FITNESSHEALTH"
What is the best way to replace all special characters with their full names in a String Java?
One approach here would be to maintain a hashmap containing all symbols and their name replacements. Then, do a regex iteration over the input string and make all replacements.
Map<String, String> terms = new HashMap<>();
terms.put(".", " Fullstop ");
terms.put("!", " Exclamation mark ");
terms.put("\"", " Double quote ");
terms.put("#", " Hashtag ");
String input = "The quick! brown #fox \"jumps\" over the lazy dog.";
Pattern pattern = Pattern.compile("[.!\"#]");
Matcher matcher = pattern.matcher(input);
StringBuffer buffer = new StringBuffer();
while (matcher.find()) {
matcher.appendReplacement(buffer, terms.get(matcher.group(0)));
}
matcher.appendTail(buffer);
System.out.println("input: " + input);
System.out.println("output: " + buffer.toString());
This prints:
input: The quick! brown #fox "jumps" over the lazy dog.
output: The quick Exclamation mark brown Hashtag fox Double quote jumps Double quote over the lazy dog Fullstop
The above approach appears a bit verbose, but in practice all the core replacement logic is happening within a one line while loop. If you are on Java 8, you could also use a Matcher stream approach, but the logic would be more or less the same.
Replace multiple (special) characters - most efficient way?
For an efficient solution you could use str.maketrans for this. Note that once the translation table is defined, it's onle a matter of mapping the characters in the string. Here's how you could do so:
symbols = ["`", "~", "!", "@", "#", "$", "%", "^", "&", "*", "(", ")", "_", "-", "+",
"=", "{", "[", "]", "}", "|", "\\", ":", ";", "\"", "<", ",", ">", ".", "?", "/"]
Start by creating a dictionary from the symbols using dict.fromkeys setting a single space as value for each entry and create a translation table from the dictionary:
d = dict.fromkeys(''.join(symbols), ' ')
# {'`': ' ', ',': ' ', '~': ' ', '!': ' ', '@': ' '...
t = str.maketrans(d)
Then call the string translate method to map the characters in the above dictionary with an empty space:
s = '~this@is!a^test@'
s.translate(t)
# ' this is a test '
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