What is the best way to compare two strings to see how similar they are?

Examples:

    My String
    My String With Extra Words

Or

    My String
    My Slightly Different String

What I am looking for is to determine how similar the first and second string in each pair is. I would like to score the comparison and if the strings are similar enough, I would consider them a matching pair.

Is there a good way to do this in C#?

Compare string similarity

I have two strings which I&#39;d like to compare: `String` and `String:`. Is there a library function that would return true when passed these two strings, but false for say `String` and `OtherString`?

To be precise, I want to know whether one string is a prefix of another.

Check if one string is a prefix of another

I&#39;m reading encrypted credentials/connection strings from a config file. Resharper tells me, &quot;String.IndexOf(string) is culture-specific here&quot; on this line:

    if (line.Contains(&quot;host=&quot;)) {
    	_host = line.Substring(line.IndexOf(
    		&quot;host=&quot;) + &quot;host=&quot;.Length, line.Length - &quot;host=&quot;.Length);

...and so wants to change it to:

    if (line.Contains(&quot;host=&quot;)) {
    	_host = line.Substring(line.IndexOf(&quot;host=&quot;, System.StringComparison.Ordinal) + &quot;host=&quot;.Length, line.Length - 	&quot;host=&quot;.Length);

The value I&#39;m reading will always be &quot;host=&quot; regardless of where the app may be deployed. Is it really sensible to add this &quot;System.StringComparison.Ordinal&quot; bit? 

More importantly, could it hurt anything (to use it)?

Could string comparisons really differ based on culture when the string is guaranteed not to change?

I&#39;m trying to get a case-insensitive search with two strings in JavaScript working.

Normally it would be like this:

    var string=&quot;Stackoverflow is the BEST&quot;;
    var result= string.search(/best/i);
    alert(result);

The `/i` flag would be for case-insensitive.

But I need to search for a second string; without the flag it works perfect:

    var string=&quot;Stackoverflow is the BEST&quot;;
    var searchstring=&quot;best&quot;;
    var result= string.search(searchstring);
    alert(result);

If I add the `/i` flag to the above example it would search for searchstring and not for what is in the variable &quot;searchstring&quot; (next example not working):

    var string=&quot;Stackoverflow is the BEST&quot;;
    var searchstring=&quot;best&quot;;
    var result= string.search(/searchstring/i);
    alert(result);

How can I achieve this?

Case-insensitive search

I&#39;m trying to compare a character array against a string like so:

    const char *var1 = &quot; &quot;;
    var1 = getenv(&quot;myEnvVar&quot;);
    
    if(var1 == &quot;dev&quot;)
    {
       // do stuff
    }

This if statement never validates as true... when I output var1 it is &quot;dev&quot;, I was thinking maybe it has something to do with a null terminated string, but the strlen of &quot;dev&quot; and var1 are equal... I also thought maybe var1 == &quot;dev&quot; was comparing &quot;dev&quot; against the memory location of var1 instead of the value. *var1 == &quot;dev&quot; results in an error.... tried many things, probably a simple solution for the saavy c++ developer (I havent coded c++ in a looong time).


edit:
we&#39;ve tried

    if(strcmp(var1, &quot;dev&quot;) == 0)

and 

    if(strncmp(var1, &quot;dev&quot;, 3) == 0)


Thanks


edit: After testing at home I&#39;m just going to suggest my co-worker changes the datatype to a string. I believe he was comparing a char array of a large size against a string. I put together a program that outputs sizeof, strlen, etc to help us work through it. Thanks to everyone for the help.


C++ Compare char array with string

How can I make the line below case insensitive?

    drUser[&quot;Enrolled&quot;] = 
          (enrolledUsers.FindIndex(x =&gt; x.Username == (string)drUser[&quot;Username&quot;]) != -1);

I was given some advice earlier today that suggested I use: 

    x.Username.Equals((string)drUser[&quot;Username&quot;], StringComparison.OrdinalIgnoreCase)));

the trouble is I can&#39;t get this to work, I&#39;ve tried the line below, this compiles but returns the wrong results, it returns enrolled users as unenrolled and unenrolled users as enrolled.

    drUser[&quot;Enrolled&quot;] = 
          (enrolledUsers.FindIndex(x =&gt; x.Username.Equals((string)drUser[&quot;Username&quot;], 
                                     StringComparison.OrdinalIgnoreCase)));

Can anyone point out the problem?

How can I do a case insensitive string comparison?

What is the correct way to check for equality between Strings in JavaScript?

What is the correct way to check for string equality in JavaScript?

I&#39;m looking for a Python module that can do simple fuzzy string comparisons.  Specifically, I&#39;d like a percentage of how similar the strings are.  I know this is potentially subjective so I was hoping to find a library that can do positional comparisons as well as longest similar string matches, among other things.

Basically, I&#39;m hoping to find something that is simple enough to yield a single percentage while still configurable enough that I can specify what type of comparison(s) to do.

Good Python modules for fuzzy string comparison?

I am trying to compare strings in bash. I already found an answer on how to do it on [stackoverflow][1]. In script I am trying, I am using the code submitted by Adam in the mentioned question:

    #!/bin/bash
    string=&#39;My string&#39;;
    
    if [[ &quot;$string&quot; == *My* ]]
    then
      echo &quot;It&#39;s there!&quot;;
    fi
    
    needle=&#39;y s&#39;
    if [[ &quot;$string&quot; == *&quot;$needle&quot;* ]]; then
      echo &quot;haystack &#39;$string&#39; contains needle &#39;$needle&#39;&quot;
    fi

I also tried approach from [ubuntuforums][2] that you can find in 2nd post

    if [[ $var =~ regexp ]]; then
      #do something
    fi

In both cases I receive error:

    [[: not found

What am I doing wrong?
  [1]: https://stackoverflow.com/questions/229551/string-contains-in-bash
  [2]: http://ubuntuforums.org/showthread.php?t=562398

String comparison in bash. [[: not found

How do I compare two strings in Perl?

I am learning Perl, I had this basic question looked it up here on StackOverflow and found no good answer so I thought I would ask.

How do I compare two strings in Perl?

I want `apple` and `Apple` comparison to be `true`.
Currently


    &quot;Apple&quot; == &quot;Apple&quot;  # returns TRUE
    &quot;Apple&quot; == &quot;APPLE&quot;  # returns FALSE


How to compare strings ignoring the case

When comparing two strings in c# for equality, what is the difference between InvariantCulture and Ordinal comparison?

Difference between InvariantCulture and Ordinal string comparison

I want to compare several strings to each other, and find the ones that are the most similar.  I was wondering if there is any library, method or best practice that would return me which strings are more similar to other strings.  For example:

 - &quot;The quick fox jumped&quot; -&gt; &quot;The fox jumped&quot; 
 - &quot;The quick fox jumped&quot; -&gt;  &quot;The fox&quot;

This comparison would return that the first is more similar than the second.

I guess I need some method such as:

    double similarityIndex(String s1, String s2)

Is there such a thing somewhere?

EDIT: Why am I doing this? I am writing a script that compares the output of a MS Project file to the output of some legacy system that handles tasks.  Because the legacy system has a very limited field width, when the values are added the descriptions are abbreviated.  I want some semi-automated way to find which entries from MS Project are similar to the entries on the system so I can get the generated keys.  It has drawbacks, as it has to be still manually checked, but it would save a lot of work

Similarity String Comparison in Java

How can I check whether a string is not null and not empty?

    public void doStuff(String str)
    {
		if (str != null &amp;&amp; str != &quot;**here I want to check the &#39;str&#39; is empty or not**&quot;)
		{
			/* handle empty string */
		}
        /* ... */
	}

Check whether a string is not null and not empty

I fall into a surprising issue. 

I loaded a text file in my application and I have some logic which compares the value having &#181;.

And I realized that even if the texts are same the compare value is false.

     Console.WriteLine(&quot;μ&quot;.Equals(&quot;&#181;&quot;)); // returns false
     Console.WriteLine(&quot;&#181;&quot;.Equals(&quot;&#181;&quot;)); // return true

In later line the character  &#181; is copy pasted.

Any idea will be helpful.



How to compare &#39;μ&#39; and &#39;&#181;&#39; in C#

Why does the following statement return `true`?

    &quot;608E-4234&quot; == &quot;272E-3063&quot;

I have also tried this with single quotes around the strings. The only way I can get it to evaulate to `false` is by using the `===` operator instead of `==`

My guess is PHP is treating it as some sort of equation but it seems a bit of a strange one.

Can anybody elaborate?

Why does PHP convert a string with the letter E into a number?

I would like to know how to check whether a string starts with &quot;hello&quot; in Python.

In Bash I usually do:

    if [[ &quot;$string&quot; =~ ^hello ]]; then
     do something here
    fi

How do I achieve the same in Python?

Checking whether a string starts with XXXX

In C there is a `switch` construct which enables one to execute different conditional branches of code based on an test integer value, e.g.,

```c
int a;
/* Read the value of &quot;a&quot; from some source, e.g. user input */
switch (a) {
  case 100:
    // Code
    break;
  case 200:
    // Code
    break;
  default:
    // Code
    break;
}
```

How is it possible to obtain the same behavior (i.e. avoid the so-called &quot;`if`-`else` ladder&quot;) for a string value, i.e., a `char *`?

How can I compare strings in C using a `switch` statement?

I fall into a surprising issue. 

I loaded a text file in my application and I have some logic which compares the value having &#181;.

And I realized that even if the texts are same the compare value is false.

     Console.WriteLine(&quot;μ&quot;.Equals(&quot;&#181;&quot;)); // returns false
     Console.WriteLine(&quot;&#181;&quot;.Equals(&quot;&#181;&quot;)); // return true

In later line the character  &#181; is copy pasted.

However, these might not be the only characters that are like this.

Is there any way in C# to compare the characters which look the same but are actually different?

How to compare Unicode characters that &quot;look alike&quot;?

I want to write a `cmp`-like function that compares two version numbers and returns `-1`, `0`, or `1` based on their compared values.

 - Return `-1` if version A is older than version B
 - Return `0` if versions A and B are equivalent
 - Return `1` if version A is newer than version B

Each subsection is supposed to be interpreted as a number, therefore 1.10 &gt; 1.1. 

Desired function outputs are

    mycmp(&#39;1.0&#39;, &#39;1&#39;) == 0
    mycmp(&#39;1.0.0&#39;, &#39;1&#39;) == 0
    mycmp(&#39;1&#39;, &#39;1.0.0.1&#39;) == -1
    mycmp(&#39;12.10&#39;, &#39;11.0.0.0.0&#39;) == 1
    ...

And here is my implementation, open for improvement:


    def mycmp(version1, version2):
        parts1 = [int(x) for x in version1.split(&#39;.&#39;)]
        parts2 = [int(x) for x in version2.split(&#39;.&#39;)]

        # fill up the shorter version with zeros ...
        lendiff = len(parts1) - len(parts2)
        if lendiff &gt; 0:
            parts2.extend([0] * lendiff)
        elif lendiff &lt; 0:
            parts1.extend([0] * (-lendiff))
    
        for i, p in enumerate(parts1):
            ret = cmp(p, parts2[i])
            if ret: return ret
        return 0

I&#39;m using Python 2.4.5 btw. (installed at my working place ...).

Here&#39;s a small &#39;test suite&#39; you can use

    assert mycmp(&#39;1&#39;, &#39;2&#39;) == -1
    assert mycmp(&#39;2&#39;, &#39;1&#39;) == 1
    assert mycmp(&#39;1&#39;, &#39;1&#39;) == 0
    assert mycmp(&#39;1.0&#39;, &#39;1&#39;) == 0
    assert mycmp(&#39;1&#39;, &#39;1.000&#39;) == 0
    assert mycmp(&#39;12.01&#39;, &#39;12.1&#39;) == 0
    assert mycmp(&#39;13.0.1&#39;, &#39;13.00.02&#39;) == -1
    assert mycmp(&#39;1.1.1.1&#39;, &#39;1.1.1.1&#39;) == 0
    assert mycmp(&#39;1.1.1.2&#39;, &#39;1.1.1.1&#39;) == 1
    assert mycmp(&#39;1.1.3&#39;, &#39;1.1.3.000&#39;) == 0
    assert mycmp(&#39;3.1.1.0&#39;, &#39;3.1.2.10&#39;) == -1
    assert mycmp(&#39;1.1&#39;, &#39;1.10&#39;) == -1




Version number comparison in Python

I have two strings like

    string1=&quot;abc def ghi&quot;

and

    string2=&quot;def ghi abc&quot;

How to get that this two string are same without breaking the words?

How do I compare two strings in python if order does not matter?

I was unable to find this on php.net. Is the double equal sign (`==`) case sensitive when used to compare strings in PHP?

Is == in PHP a case-sensitive string comparison?

I have two postcodes `char*` that I want to compare, ignoring case.
Is there a function to do this?

Or do I have to loop through each use the `tolower` function and then do the comparison?

Any idea how this function will react with numbers in the string

Thanks

Case Insensitive String Comparison in C

Both the following comparisons evaluate to true:

1)

    @&quot;foo&quot; == @&quot;foo&quot;;

2)

    NSString *myString1 = @&quot;foo&quot;;
    NSString *myString2 = @&quot;foo&quot;;
    myString1 == myString2;

However, there are definitely times where two `NSString`s cannot be compared using the equality operator, and `[myString1 isEqualToString:myString2]` is required instead.  Can someone shed some light on this?

Understanding NSString comparison

I need a way to compare multiple strings to a test string and return the string that closely resembles it:

    TEST STRING: THE BROWN FOX JUMPED OVER THE RED COW
    
    CHOICE A   : THE RED COW JUMPED OVER THE GREEN CHICKEN
    CHOICE B   : THE RED COW JUMPED OVER THE RED COW
    CHOICE C   : THE RED FOX JUMPED OVER THE BROWN COW

(If I did this correctly) The closest string to the &quot;TEST STRING&quot; should be &quot;CHOICE C&quot;.  What is the easiest way to do this?

I plan on implementing this into multiple languages including VB.net, Lua, and JavaScript.  At this point, pseudo code is acceptable.  If you can provide an example for a specific language, this is appreciated too!

Getting the closest string match

What does &quot;compare two strings lexicographically&quot; mean?



String Comparison in Java

I need to compare strings  to decide whether they represent the same thing.  This relates to case titles entered by humans where abbreviations and other small details may differ.  For example, consider the following two titles:

    std::string first = &quot;Henry C. Harper v. The Law Offices of Huey &amp; Luey, LLP&quot;;

As opposed to:

    std::string second = &quot;Harper v. The Law Offices of Huey &amp; Luey, LLP&quot;;

A human can quickly gauge that these are most likely one and the same.  The current approach I have taken is to normalize the strings by lowercasing all letters and removing all punctuation and spaces giving:

    std::string firstNormalized = &quot;henrycharpervthelawofficesofhueylueyllp&quot;;

And:

    std::string secondNormalized = &quot;harpervthelawofficesofhueylueyllp&quot;;

Comparing in this case, one is a sub-sequence of the other, but you can imagine other more complex variations where that does not necessarily occur, yet they have significant sub-sequences in common.  There could also be occasional human entry errors such as transposed letters and spelling errors.

Perhaps some kind of character diff program could help?  I&#39;ve seen good line diff programs for comparing differences in code to be checked in, is there something like that on a character basis, maybe in boost?  If you could count the number of consecutive characters in common and take the ratio to the characters unshared, perhaps that would be a good heuristic?

In the end, I need a Boolean decision as to whether to consider them the same or not.  It doesn&#39;t have to be perfect, but it should ideally rarely be wrong.

What algorithm can I use that will give me some kind of quantification as to how similar the two strings are to each other which I can then convert into a yes/no answer by way of some heuristic?

What are some algorithms for comparing how similar two strings are?

I&#39;m looking for a way to compare a string with an array of strings. Doing an exact search is quite easy of course, but I want my program to tolerate spelling mistakes, missing parts of the string and so on.

Is there some kind of framework which can perform such a search? I&#39;m having something in mind that the search algorithm will return a few results order by the percentage of match or something like this.

Comparing strings with tolerance

Is there a simple ignore-case-comparison for PostgreSQL?

I want to replace:

    SELECT id, user_name 
        FROM users 
            WHERE lower(email) IN (lower(&#39;adamB@a.com&#39;), lower(&#39;eveA@b.com&#39;));

With something like:

    SELECT id, user_name 
        FROM users 
            WHERE email IGNORE_CASE_IN (&#39;adamB@a.com&#39;, &#39;eveA@b.com&#39;);

The `like` and `ilike` operators work on single values (e.g. `like &#39;adamB@a.com&#39;`), but not on sets.

PostgreSQL: Case insensitive string comparison

I&#39;ve been trying to figure out how I can make a query with MySQL that checks if the value (string `$haystack` ) in a certain column contains certain data (string `$needle`), like this:

    SELECT *
    FROM `table`
    WHERE `column`.contains(&#39;{$needle}&#39;)


In PHP, the function is called `substr($haystack, $needle)`, so maybe:

    WHERE substr(`column`, &#39;{$needle}&#39;)=1

MySQL query String contains

I am learning `fuzzywuzzy` in Python.

I understand the concept of `fuzz.ratio`, `fuzz.partial_ratio`, `fuzz.token_sort_ratio` and `fuzz.token_set_ratio`. My question is when to use which function?

 - Do I check the 2 strings&#39; length first, say if not similar, then rule
   out `fuzz.partial_ratio`?
 - If the 2 strings&#39; length are similar, I&#39;ll use
   `fuzz.token_sort_ratio`?   
 - Should I always use `fuzz.token_set_ratio`?

Anyone knows what criteria SeatGeek uses?

I am trying to build a real estate website, thinking to use `fuzzywuzzy` to compare addresses.

When to use which fuzz function to compare 2 strings

I am walking a directory that contains eggs to add those eggs to the `sys.path`.  If there are two versions of the same .egg in the directory, I want to add only the latest one.

I have a regular expression `r&quot;^(?P&lt;eggName&gt;\w+)-(?P&lt;eggVersion&gt;[\d\.]+)-.+\.egg$` to extract the name and version from the filename.  The problem is comparing the version number, which is a string like `2.3.1`.

Since I&#39;m comparing strings, 2 sorts above 10, but that&#39;s not correct for versions.

    &gt;&gt;&gt; &quot;2.3.1&quot; &gt; &quot;10.1.1&quot;
    True

I could do some splitting, parsing, casting to int, etc., and I would eventually get a workaround.  But this is Python, [not Java][1].  Is there an elegant way to compare version strings?

  [1]: https://stackoverflow.com/questions/6701948/efficient-way-to-compare-version-strings-in-java

How do I compare version numbers in Python?

I have a function that returns five characters with mixed case. If I do a query on this string it will return the value regardless of case.

How can I make MySQL string queries case sensitive?

How can I make SQL case sensitive string comparison on MySQL?

Why does `&quot;hello&quot; is &quot;hello&quot;` produce `True` in Python?

I read the following [here](http://zetcode.com/tutorials/pythontutorial/keywords/):

 &gt; If two string literals are equal, they have been put to same
 memory location. A string is an immutable entity. No harm can
 be done.

So there is one and only one place in memory for every Python string? Sounds pretty strange. What&#39;s going on here?

Python: Why does (&quot;hello&quot; is &quot;hello&quot;) evaluate as True?

In PowerShell I have an array of string objects, and I have an object that contains string objects. In Java you can do a `.equals(aObject)` to test if the string values match, whereas doing a `==` test if the two objects refer to the same location in memory.

How do I run an equivalent `.equals(aObject)` in powershell?

I&#39;m doing this:

    $arrayOfStrings[0].Title -matches $myObject.item(0).Title

These both have the exact same string values, but I get a return value of false. Any suggestions?


How to compare the contents of two string objects in PowerShell

While answering [this question][1], I became uncertain about something that I didn&#39;t manage to find a sufficient answer to.

What are the practical differences between using the binary `utf8_bin` and the case insensitive `utf8_general_ci` collations? 

I can see three:

 1. Both have a different sorting order; `_bin`&#39;s sorting order is likely to put any umlauts to the end of the alphabet, because byte values are compared (right?)

 2. Only case sensitive searches in `_bin` 

 3. No `A = &#196;` equality in `_bin`

Are there any other differences or side-effects to be aware of?




Reference:

 * [9.1.2. Character Sets and Collations in MySQL][2]
 * [9.1.7.6. The _bin and binary Collations][3] in the mySQL manual
 * [9.1.7.7. The BINARY Operator][4]

Similar questions that don&#39;t address the issue:

 * https://stackoverflow.com/questions/2344118/utf-8-general-bin-unicode 


  [1]: https://stackoverflow.com/questions/5526169/what-is-the-best-mysql-collation-for-german-language/5526189#5526189
  [2]: http://dev.mysql.com/doc/refman/5.0/en/charset-mysql.html
  [3]: http://dev.mysql.com/doc/refman/5.0/en/charset-binary-collations.html
  [4]: http://dev.mysql.com/doc/refman/5.0/en/charset-binary-op.html

All String Comparison Solutions on Gang of Coders

Total of 36 String Comparison Solutions