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Reduce multiple consecutive equal characters from a string to just one

Basically, I want to take a string, and if there are multiple '+'s in a row, i want to remove all but one. So:
"This++is+an++++ex+ampl++e"
would become
"This+is+an+ex+ampl+e"
I'm not sure whether LINQ or Regex or something else would be best suited, but it doesn't have to use any particular method.

Regex.Replace(str, #"\++", "+");

while (str.Contains("++"))
str = str.Replace("++", "+");

Microsoft's Interactive Extensions (Ix) have a method called DistinctUntilChanged that does what you want. There is a bunch of useful functionality included in that library - but it is another whole library, which you might not want to bother with.
The usage would be like this:
str = new string(str
.ToEnumerable()
.DistinctUntilChanged()
.ToArray());
If you want to remove only plus signs, then you could do this:
str = new string(str
.ToEnumerable()
.Select((c, i) => new { c, i = (c != '+' ? i : -1) })
.DistinctUntilChanged()
.Select(t => t.c)
.ToArray());

There are ways to do this with less code (and #slaks showed me how much I need to relearn regex), but this should close to as fast as is possible in most cases, if you're doing it a lot.
public static string RemoveDupes(this string replaceString, char dupeChar){
if(replaceString == null || String.Length < 2){ return replaceString; }
int startOfGood = 0;
StringBuilder result = new StringBuilder();
for(int x = 0;x<replaceString.Length-1;x++){
if(replaceString[x] == dupeChar && replaceString[x+1] == dupeChar){
result.Append(replaceString.SubString(startOfGood,x-startOfGood));//I think this works with length 0
startOfGood = x+1;
}
}
result.Append(replaceString.Substring(startOfGood,
replaceString.Length-startOfGood));
return result.ToString();
}
//Usage:
var noDupes = "This++is+an++++ex+ampl++e".RemoveDupes('+');

Performing function on each array element, returning results to new array

I'm a complete Linq newbie here, so forgive me for a probably quite simple question.
I want to perform an operation on every element in an array, and return the result of each of these operations to a new array.
For example, say I have an array or numbers and a function ToWords() that converts the numbers to their word equivalents, I want to be able to pass in the numbers array, perform the ToWords() operation on each element, and pass out a string[]
I know it's entirely possible in a slightly more verbose way, but in my Linq adventures I'm wondering if it's doable in a nice one-liner.

You can use Select() to transform one sequence into another one, and ToArray() to create an array from the result:
int[] numbers = { 1, 2, 3 };
string[] strings = numbers.Select(x => ToWords(x)).ToArray();

It's pretty straight forward. Just use the Select method:
var results = array.Select(ToWords).ToArray();
Note that unless you need an array you don't have to call ToArray. Most of the time you can use lazy evaluation on an IEnumerable<string> just as easily.

There are two different approaches - you can use Select extension method or you can use select clause:
var numbers = new List<int>();
var strings1 = from num in numbers select ToWords(num);
var strings2 = numbers.Select(ToWords);
both of them will return IEnumerable<>, which you can cast as you need (for example, with .ToArray() or .ToList()).

You could do something like this :
public static string[] ProcessStrings(int[] intList)
{
return Array.ConvertAll<int, string>(intList, new Converter<int, string>(
delegate(int number)
{
return ToWords();
}));
}
If it is a list then :
public static List<string> ProcessStrings(List<int> intList)
{
return intList.ConvertAll<string>(new Converter<int, string>(
delegate(int number)
{
return ToWords();
}));
}

Straight simple:
string[] wordsArray = array.ToList().ConvertAll(n => ToWords(n)).ToArray();
If you are OK with Lists, rather than arrays, you can skip ToList() and ToArray().
Lists are much more flexible than arrays, I see no reason on earth not to use them, except for specific cases.

Can I use LINQ to strip repeating spaces from a string?

A quick brain teaser: given a string
This is a string with repeating spaces
What would be the LINQ expressing to end up with
This is a string with repeating spaces
Thanks!
For reference, here's one non-LINQ way:
private static IEnumerable<char> RemoveRepeatingSpaces(IEnumerable<char> text)
{
bool isSpace = false;
foreach (var c in text)
{
if (isSpace && char.IsWhiteSpace(c)) continue;
isSpace = char.IsWhiteSpace(c);
yield return c;
}
}

This is not a linq type task, use regex
string output = Regex.Replace(input," +"," ");
Of course you could use linq to apply this to a collection of strings.

public static string TrimInternal(this string text)
{
var trimmed = text.Where((c, index) => !char.IsWhiteSpace(c) || (index != 0 && !char.IsWhiteSpace(text[index - 1])));
return new string(trimmed.ToArray());
}

Since nobody seems to have given a satisfactory answer, I came up with one. Here's a string-based solution (.Net 4):
public static string RemoveRepeatedSpaces(this string s)
{
return s[0] + string.Join("",
s.Zip(
s.Skip(1),
(x, y) => x == y && y == ' ' ? (char?)null : y));
}
However, this is just a general case of removing repeated elements from a sequence, so here's the generalized version:
public static IEnumerable<T> RemoveRepeatedElements<T>(
this IEnumerable<T> s, T dup)
{
return s.Take(1).Concat(
s.Zip(
s.Skip(1),
(x, y) => x.Equals(y) && y.Equals(dup) ? (object)null : y)
.OfType<T>());
}
Of course, that's really just a more specific version of a function that removes all consecutive duplicates from its input stream:
public static IEnumerable<T> RemoveRepeatedElements<T>(this IEnumerable<T> s)
{
return s.Take(1).Concat(
s.Zip(
s.Skip(1),
(x, y) => x.Equals(y) ? (object)null : y)
.OfType<T>());
}
And obviously you can implement the first function in terms of the second:
public static string RemoveRepeatedSpaces(this string s)
{
return string.Join("", s.RemoveRepeatedElements(' '));
}
BTW, I benchmarked my last function against the regex version (Regex.Replace(s, " +", " ")) and they were were within nanoseconds of each other, so the extra LINQ overhead is negligible compared to the extra regex overhead. When I generalized it to remove all consecutive duplicate characters, the equivalent regex (Regex.Replace(s, "(.)\\1+", "$1")) was 3.5 times slower than my LINQ version (string.Join("", s.RemoveRepeatedElements())).
I also tried the "ideal" procedural solution:
public static string RemoveRepeatedSpaces(string s)
{
StringBuilder sb = new StringBuilder(s.Length);
char lastChar = '\0';
foreach (char c in s)
if (c != ' ' || lastChar != ' ')
sb.Append(lastChar = c);
return sb.ToString();
}
This is more than 5 times faster than a regex!

In practice, I would probably just use your original solution or regular expressions (if you want a quick & simple solution). A geeky approach that uses lambda functions would be to define a fixed point operator:
T FixPoint<T>(T initial, Func<T, T> f) {
T current = initial;
do {
initial = current;
current = f(initial);
} while (initial != current);
return current;
}
This keeps calling the operation f repeatedly until the operation returns the same value that it got as an argument. You can think of the operation as a generalized loop - it is quite useful, though I guess it is too geeky to be included in .NET BCL. Then you can write:
string res = FixPoint(original, s => s.Replace(" ", " "));
It is not as efficient as your original version, but unless there are too many spaces it should work fine.

Linq is by definition related to enumerable (i.e. collections, list, arrays). You could transorm your string into a collection of char and select the non space one but this is definitevly not a job for Linq.

Paul Creasey's answer is the way to go.
If you want to treat tabs as whitespace as well, go with:
text = Regex.Replace(text, "[ |\t]+", " ");
UPDATE:
The most logical way to solve this problem while satisfying the "using LINQ" requirement has been suggested by both Hasan and Ani. However, notice that these solutions involve accessing a character in a string by index.
The spirit of the LINQ approach is that it can be applied to any enumerable sequence. Because any reasonably efficient solution to this problem requires maintaining some kind of state (with Ani's and Hasan's solutions it's easy to miss this fact as the state is already maintained within the string itself), a generic approach that accepts any sequence of items is likely going to be much more straightforward to implement using procedural code.
This procedural code may then be abstracted into a method that looks like a LINQ-style method, of course. But I would not recommend tackling a problem like this with the attitude of "I want to use LINQ in this solution" from the get-go because it will impose very awkward restriction on your code.
For what it's worth, here's how I'd implement the general idea.
public static IEnumerable<T> StripConsecutives<T>(this IEnumerable<T> source, T value, IEqualityComparer<T> comparer)
{
// null-checking omitted for brevity
using (var enumerator = source.GetEnumerator())
{
if (enumerator.MoveNext())
{
yield return enumerator.Current;
}
else
{
yield break;
}
T prev = enumerator.Current;
while (enumerator.MoveNext())
{
T current = enumerator.Current;
if (comparer.Equals(prev, value) && comparer.Equals(current, value))
{
// This is a consecutive occurrence of value --
// moving on...
}
else
{
yield return current;
}
prev = current;
}
}
}

Split to list, filter, then rejoin, 2 lines of code...
var test = " Alpha Beta Tango ";
var l = test.Split(' ').Where(s => !string.IsNullOrEmpty(s));
var result = string.Join(" ", l);
// result = "Alpha Beta Tango"
Refactoring as an extension method:
using Extensions;
void Main()
{
var test = " Alpha Beta Tango ";
var result = test.RemoveRepeatedSpaces();
// result = "Alpha Beta Tango";
}
static class Extentions
{
public static string RemoveRepeatedSpaces(this string s)
{
if (s == null)
return string.Empty;
var l = s.Split(' ').Where(a => !string.IsNullOrEmpty(a));
return string.Join(" ", l);
}
}

Can you reverse order a string in one line with LINQ or a LAMBDA expression

Not that I would want to use this practically (for many reasons) but out of strict curiousity I would like to know if there is a way to reverse order a string using LINQ and/or LAMBDA expressions in one line of code, without utilising any framework "Reverse" methods.
e.g.
string value = "reverse me";
string reversedValue = (....);
and reversedValue will result in "em esrever"
EDIT
Clearly an impractical problem/solution I know this, so don't worry it's strictly a curiosity question around the LINQ/LAMBDA construct.

Well, I can do it in one very long line, even without using LINQ or a lambda:
string original = "reverse me"; char[] chars = original.ToCharArray(); char[] reversed = new char[chars.Length]; for (int i=0; i < chars.Length; i++) reversed[chars.Length-i-1] = chars[i]; string reversedValue = new string(reversed);
(Dear potential editors: do not unwrap this onto multiple lines. The whole point is that it's a single line, as per the sentence above it and the question.)
However, if I saw anyone avoiding using framework methods for the sake of it, I'd question their sanity.
Note that this doesn't use LINQ at all. A LINQ answer would be:
string reverseValue = new string(original.Reverse().ToArray());
Avoiding using Reverse, but using OrderByDescending instead:
string reverseValue = new string(original.Select((c, index) => new { c, index })
.OrderByDescending(x => x.index)
.Select(x => x.c)
.ToArray());
Blech. I like Mehrdad's answer though. Of course, all of these are far less efficient than the straightforward approach.
Oh, and they're all wrong, too. Reversing a string is more complex than reversing the order of the code points. Consider combining characters, surrogate pairs etc...

I don't see a practical use for this but just for the sake of fun:
new string(Enumerable.Range(1, input.Length).Select(i => input[input.Length - i]).ToArray())

new string(value.Reverse().ToArray())

var reversedValue = value.ToCharArray()
.Select(ch => ch.ToString())
.Aggregate<string>((xs, x) => x + xs);

Variant with recursive lambda:
var value = "reverse me";
Func<String, String> f = null; f = s => s.Length == 1 ? s : f(s.Substring(1)) + s[0];
var reverseValue = f(value);
LP,
Dejan

You can use Aggregate to prepend each Char to the reversed string:
"reverse me".Aggregate("", (acc, c) => c + acc);

var reversedValue= "reverse me".Reverse().ToArray();

In addition to one previous post here is a more performant solution.
var actual0 = "reverse me".Aggregate(new StringBuilder(), (x, y) => x.Insert(0, y)).ToString();

public static string Reverse(string word)
{
int index = word.Length - 1;
string reversal = "";
//for each char in word
for (int i = index; index >= 0; index--)
{
reversal = reversal + (word.Substring(index, 1));
Console.WriteLine(reversal);
}
return reversal;
}
Quite simple. So, from this point on, I have a single method that reverses a string, that doesn't use any built-in Reverse functions.
So in your main method, just go,
Console.WriteLine(Reverse("Some word"));
Technically that's your one liner :P

If we need to support combining characters and surrogate pairs:
// This method tries to handle:
// (1) Combining characters
// These are two or more Unicode characters that are combined into one glyph.
// For example, try reversing "Not nai\u0308ve.". The diaresis (¨) should stay over the i, not move to the v.
// (2) Surrogate pairs
// These are Unicode characters whose code points exceed U+FFFF (so are not in "plane 0").
// To be represented with 16-bit 'char' values (which are really UTF-16 code units), one character needs *two* char values, a so-called surrogate pair.
// For example, try "The sphere \U0001D54A and the torus \U0001D54B.". The 𝕊 and the 𝕋 should be preserved, not corrupted.
var value = "reverse me"; // or "Not nai\u0308ve.", or "The sphere \U0001D54A and the torus \U0001D54B.".
var list = new List<string>(value.Length);
var enumerator = StringInfo.GetTextElementEnumerator(value);
while (enumerator.MoveNext())
{
list.Add(enumerator.GetTextElement());
}
list.Reverse();
var result = string.Concat(list);
Documentation: MSDN: System.Globalization.StringInfo Class

string str="a and b";
string t="";
char[] schar = str.Reverse().ToArray();
foreach (char c in schar )
{
test += c.ToString();
}

How to search a string in String array

I need to search a string in the string array. I dont want to use any for looping in it
string [] arr = {"One","Two","Three"};
string theString = "One"
I need to check whether theString variable is present in arr.

Well, something is going to have to look, and looping is more efficient than recursion (since tail-end recursion isn't fully implemented)... so if you just don't want to loop yourself, then either of:
bool has = arr.Contains(var); // .NET 3.5
or
bool has = Array.IndexOf(arr, var) >= 0;
For info: avoid names like var - this is a keyword in C# 3.0.

Every method, mentioned earlier does looping either internally or externally, so it is not really important how to implement it. Here another example of finding all references of target string
string [] arr = {"One","Two","Three"};
var target = "One";
var results = Array.FindAll(arr, s => s.Equals(target));

Does it have to be a string[] ? A List<String> would give you what you need.
List<String> testing = new List<String>();
testing.Add("One");
testing.Add("Two");
testing.Add("Three");
testing.Add("Mouse");
bool inList = testing.Contains("Mouse");

bool exists = arr.Contains("One");

I think it is better to use Array.Exists than Array.FindAll.

Its pretty simple. I always use this code to search string from a string array
string[] stringArray = { "text1", "text2", "text3", "text4" };
string value = "text3";
int pos = Array.IndexOf(stringArray, value);
if (pos > -1)
{
return true;
}
else
{
return false;
}

If the array is sorted, you can use BinarySearch. This is a O(log n) operation, so it is faster as looping. If you need to apply multiple searches and speed is a concern, you could sort it (or a copy) before using it.

Each class implementing IList has a method Contains(Object value). And so does System.Array.

Why the prohibition "I don't want to use any looping"? That's the most obvious solution. When given the chance to be obvious, take it!
Note that calls like arr.Contains(...) are still going to loop, it just won't be you who has written the loop.
Have you considered an alternate representation that's more amenable to searching?
A good Set implementation would perform well. (HashSet, TreeSet or the local equivalent).
If you can be sure that arr is sorted, you could use binary search (which would need to recurse or loop, but not as often as a straight linear search).

You can use Find method of Array type. From .NET 3.5 and higher.
public static T Find<T>(
T[] array,
Predicate<T> match
)
Here is some examples:
// we search an array of strings for a name containing the letter “a”:
static void Main()
{
string[] names = { "Rodney", "Jack", "Jill" };
string match = Array.Find (names, ContainsA);
Console.WriteLine (match); // Jack
}
static bool ContainsA (string name) { return name.Contains ("a"); }
Here’s the same code shortened with an anonymous method:
string[] names = { "Rodney", "Jack", "Jill" };
string match = Array.Find (names, delegate (string name)
{ return name.Contains ("a"); } ); // Jack
A lambda expression shortens it further:
string[] names = { "Rodney", "Jack", "Jill" };
string match = Array.Find (names, n => n.Contains ("a")); // Jack

At first shot, I could come up with something like this (but it's pseudo code and assuming you cannot use any .NET built-in libaries). Might require a bit of tweaking and re-thinking, but should be good enough for a head-start, maybe?
int findString(String var, String[] stringArray, int currentIndex, int stringMaxIndex)
{
if currentIndex > stringMaxIndex
return (-stringMaxIndex-1);
else if var==arr[currentIndex] //or use any string comparison op or function
return 0;
else
return findString(var, stringArray, currentIndex++, stringMaxIndex) + 1 ;
}
//calling code
int index = findString(var, arr, 0, getMaxIndex(arr));
if index == -1 printOnScreen("Not found");
else printOnScreen("Found on index: " + index);

In C#, if you can use an ArrayList, you can use the Contains method, which returns a boolean:
if MyArrayList.Contains("One")

You can check the element existence by
arr.Any(x => x == "One")

it is old one ,but this is the way i do it ,
enter code herevar result = Array.Find(names, element => element == "One");

I'm surprised that no one suggested using Array.IndexOf Method.
Indeed, Array.IndexOf has two advantages :
It allows searching if an element is included into an array,
It gets at the same time the index into the array.
int stringIndex = Array.IndexOf(arr, theString);
if (stringIndex >= 0)
{
// theString has been found
}
Inline version :
if (Array.IndexOf(arr, theString) >= 0)
{
// theString has been found
}

Using Contains()
string [] SomeArray = {"One","Two","Three"};
bool IsExist = SomeArray.Contains("One");
Console.WriteLine("Is string exist: "+ IsExist);
Using Find()
string [] SomeArray = {"One","Two","Three"};
var result = Array.Find(SomeArray, element => element == "One");
Console.WriteLine("Required string is: "+ result);
Another simple & traditional way, very useful for beginners to build logic.
string [] SomeArray = {"One","Two","Three"};
foreach (string value in SomeArray) {
if (value == "One") {
Console.WriteLine("Required string is: "+ value);
}
}