Code used to calculate string similarity in PHP

In php, the string similarity similar_text function and the similarity levenshtein function are described in detail. next we will introduce in detail the string similarity introduction similar_text-calculate the similarity between two strings.
Int similar_text (string $ first, string $ second [, float & $ percent])
$ First is required. Specifies the first string to be compared.
$ Second is required. Specifies the second string to be compared.
$ Percent is optional. Specifies the name of the variable that stores the percentage similarity.

The similarity between the two strings is calculated based on the description of Oliver [1993. Note that this implementation does not use the stack in the Oliver virtual code, but is called recursively. This may cause the whole process to slow down or become faster. Note that the complexity of this algorithm is O (N ** 3), and N is the length of the longest string.

For example, we want to find the similarity between the string abcdefg and the string aeg:

The code is as follows:

$ First = "abcdefg ";
$ Second = "aeg ";
Echo similar_text ($ first, $ second); result output 3. if you want to display it as a percentage, you can use its third parameter, as shown below:
$ First = "abcdefg ";
$ Second = "aeg ";
Similar_text ($ first, $ second, $ percent );
Echo $ percent;

Use and implementation of the similar_text function. The similar_text () function is mainly used to calculate the number of matching characters of two strings. It can also calculate the similarity between two strings (expressed in percentages ). Compared with the similar_text () function, the levenshtein () function we will introduce today is faster. However, the similar_text () function provides more accurate results with fewer necessary modifications. The levenshtein () function can be used when the speed is less accurate and the string length is limited.

Instructions for Use

Let's take a look at the levenshtein () function instructions in the manual:

The levenshtein () function returns the Levenshtein distance between two strings.

Levenshtein distance, also known as the editing distance, refers to the minimum number of edits required to convert a string from one to another. Licensed editing operations include replacing one character with another, inserting one character, and deleting one character.

For example, convert kitten to sitting:

Sitten (k → s)
Sittin (e → I)
The sitting (→ g) levenshtein () function gives each operation the same weight (replacement, insertion, and deletion. However, you can set optional insert, replace, and delete parameters to define the cost of each operation.

Syntax:

Levenshtein (string1, string2, insert, replace, delete)

Parameter description

• String1 is required. The first string to be compared.
• String2 is required. The second string to be compared.
• Insert is optional. The cost of inserting a character. The default value is 1.
• Replace is optional. The cost of replacing a character. The default value is 1.
• Delete is optional. The cost of deleting a character. The default value is 1.
Tips and comments

• If one of the strings exceeds 255 characters, the levenshtein () function returns-1.
• The levenshtein () function is case insensitive.
• The levenshtein () function is faster than the similar_text () function. However, the similar_text () function provides more accurate results that require less modification.
Example

The code is as follows:

<? Php
Echo levenshtein ("Hello World", "ello World ");
Echo"
";
Echo levenshtein ("Hello World", "ello World", 10, 20, 30 );
?>

Output: 1 30

The following is a supplement:

By default, php has a function similar_text () used to calculate the similarity between strings. This function can also calculate the similarity between two strings (expressed in percentages ). However, this function is not accurate in Chinese computing, for example:

The code is as follows:

Echo similar_text ("112 people were killed in a fire in Jilin poultry company", "112 people were killed in a fire in Jilin Baoyuanfeng Poultry Company ");

The two news titles are actually the same. if similar_text () is used for similarity, the result is: 42, that is, it is only similar to 42%, so this feeling is very unreliable, today, I just collected a piece of PHP code that is used to compare the similarity between two strings and paste the code directly:

<? Php class LCS {var $ str1; var $ str2; var $ c = array ();/* returns the longest common subsequence of string 1 and string 2 */function getLCS ($ str1, $ str2, $ len1 = 0, $ len2 = 0) {$ this-> str1 = $ str1; $ this-> str2 = $ str2; if ($ len1 = 0) $ len1 = strlen ($ str1); if ($ len2 = 0) $ len2 = strlen ($ str2); $ this-> initC ($ len1, $ len2 ); return $ this-> printLCS ($ this-> c, $ len1-1, $ len2-1);}/* returns the similarity of two strings */function getSimilar ($ str1, $ str2) {$ len1 = strlen ($ str1); $ len2 = strlen ($ str2); $ len = strlen ($ this-> getLCS ($ str1, $ str2, $ len1, $ len2); return $ len * 2/($ len1 + $ len2);} function initC ($ len1, $ len2) {for ($ I = 0; $ I <$ len1; $ I ++) $ this-> c [$ I] [0] = 0; for ($ j = 0; $ j <$ len2; $ j ++) $ this-> c [0] [$ j] = 0; for ($ I = 1; $ I <$ len1; $ I ++) {for ($ j = 1; $ j <$ len2; $ j ++) {if ($ this-> str1 [$ I] ==$ this-> str2 [$ j]) {$ this-> c [$ I] [$ j] = $ this-> c [$ I-1] [$ j-1] + 1 ;} else if ($ this-> c [$ I-1] [$ j] >=$ this-> c [$ I] [$ j-1]) {$ this-> c [$ I] [$ j] = $ this-> c [$ I-1] [$ j];} else {$ this-> c [$ I] [$ j] = $ this-> c [$ I] [$ j-1] ;}}} function printLCS ($ c, $ I, $ j) {if ($ I = 0 | $ j = 0) {if ($ this-> str1 [$ I] ==$ this-> str2 [$ j]) return $ this-> str2 [$ j]; else return "";} if ($ this-> str1 [$ I] ==$ this-> str2 [$ j]) {return $ this-> printLCS ($ this-> c, $ I-1, $ j-1 ). $ this-> str2 [$ j];} else if ($ this-> c [$ I-1] [$ j] >=$ this-> c [$ I] [$ j-1]) {return $ this-> printLCS ($ this-> c, $ I-1, $ j);} else {return $ this-> printLCS ($ this-> c, $ I, $ j-1) ;}}$ lcs = new LCS (); // returns the longest common subsequence $ lcs-> getLCS ("hello word ", "hello china"); // returns similarity echo $ lcs-> getSimilar ("Jilin poultry company killed 112 people in a fire ", "112 people have been killed in a fire in Jilin Baoyuanfeng Poultry Company ");

The output result is 0.90322580645161, which is much more accurate.