I'm preparing some table names for an ORM, and I want to turn plural table names into single entity names. My only problem is finding an algorithm that does it reliably. Here's what I'm doing right now:
Does anyone know of a better algorithm?
Those are all general rules (and good ones) but English is not a language for the faint of heart :-).
My own preference would be to have a transformation engine along with a set of transformations (surprisingly enough) for doing the actual work.
You would run through the transformations (from specific to general) and, when a match was found, apply the transformation to the word.
Regular expressions would be an ideal approach to this due to their expressiveness. An example rule set:
1. If the word is fish, return fish.
2. If the word is sheep, return sheep.
3. If the word is "radii", return "radius".
4. If the word is "types", return "type".
5. If the word ends in "ii", replace that "ii" with "us" (octopii,virii).
: : : : :
97. If a word ends with -ies, I replace the ending with -y
98. If a word ends with -es, I remove this ending.
99. Otherwise, I just remove the trailing -s.
Note that an earlier version of the rules may not have had entry number 4. However, when we found the problem with "types" being transformed to "typ" at 98, we then created a higher-priority transformation at 4 to cater for this.
You'll basically need to keep this transformation table updated as you find all those wondrous exceptions that English has spawned.
The other possibility is to not waste your time with a general rule. Since the names of the tables will be relatively limited, just create another table (or some sort of data structure) called singulars which maps all the relevant plural table names (employees) to singular object names (employee).
Then every time a table is added, add an entry to the singulars "table" so you can singularize it.
The problem is that's based on the general rules, but English has (figuratively) a billion exceptions... What do you do with words like "fish", or "geese"?
Also, the rules are for how to turn singular nouns to plurals. The reverse mapping isn't necessarily possible (consider "freebies").
Andrew Peters has a class called Inflector.NET which provides plural-to-singular and singular-to-plural methods. As Tal has pointed out no algorithm is infallible but this covers a decent number of irregular English nouns.
Maybe take a look at source code of something like Rails Inflector
See also this answer, which recommends using Morpha (or studying the algorithm behind it).
If you know that the words that you want to lemmatize are plural nouns then you can tag them with NNS to get a more accurate output.
Input example:
$ cat test.txt
Types_NNS
Pies_NNS
Trees_NNS
Buses_NNS
Radii_NNS
Communities_NNS
Sheep_NNS
Fish_NNS
Output example:
$ cat test.txt | ./morpha -c
Type
Pie
Tree
Bus
Radius
Community
Sheep
Fish
As an improvement, you could use rules that generate multiple possibilities and then look up the results in a dictionary to weed out impossible options.
For example replace -ies with -y and -ie. Pies becomes Py and Pie. Only one of those is in the dictionary, so choose that one.
Perhaps you can even find a dictionary with frequency information and select the most common word you generate.
If you combine this with an ordered list of rules that covers a few exceptions, you might get pretty good accuracy.
Maybe you need this,It works well ,if you know how to use PHP script.It can turn plural words to single words,and turn single words to plural words too.
class BaseInflector
{
/**
* @var array the rules for converting a word into its plural form.
* The keys are the regular expressions and the values are the corresponding replacements.
*/
public static $plurals = [
'/([nrlm]ese|deer|fish|sheep|measles|ois|pox|media)$/i' => '\1',
'/^(sea[- ]bass)$/i' => '\1',
'/(m)ove$/i' => '\1oves',
'/(f)oot$/i' => '\1eet',
'/(h)uman$/i' => '\1umans',
'/(s)tatus$/i' => '\1tatuses',
'/(s)taff$/i' => '\1taff',
'/(t)ooth$/i' => '\1eeth',
'/(quiz)$/i' => '\1zes',
'/^(ox)$/i' => '\1\2en',
'/([m|l])ouse$/i' => '\1ice',
'/(matr|vert|ind)(ix|ex)$/i' => '\1ices',
'/(x|ch|ss|sh)$/i' => '\1es',
'/([^aeiouy]|qu)y$/i' => '\1ies',
'/(hive)$/i' => '\1s',
'/(?:([^f])fe|([lr])f)$/i' => '\1\2ves',
'/sis$/i' => 'ses',
'/([ti])um$/i' => '\1a',
'/(p)erson$/i' => '\1eople',
'/(m)an$/i' => '\1en',
'/(c)hild$/i' => '\1hildren',
'/(buffal|tomat|potat|ech|her|vet)o$/i' => '\1oes',
'/(alumn|bacill|cact|foc|fung|nucle|radi|stimul|syllab|termin|vir)us$/i' => '\1i',
'/us$/i' => 'uses',
'/(alias)$/i' => '\1es',
'/(ax|cris|test)is$/i' => '\1es',
'/s$/' => 's',
'/^$/' => '',
'/$/' => 's',
];
/**
* @var array the rules for converting a word into its singular form.
* The keys are the regular expressions and the values are the corresponding replacements.
*/
public static $singulars = [
'/([nrlm]ese|deer|fish|sheep|measles|ois|pox|media|ss)$/i' => '\1',
'/^(sea[- ]bass)$/i' => '\1',
'/(s)tatuses$/i' => '\1tatus',
'/(f)eet$/i' => '\1oot',
'/(t)eeth$/i' => '\1ooth',
'/^(.*)(menu)s$/i' => '\1\2',
'/(quiz)zes$/i' => '\\1',
'/(matr)ices$/i' => '\1ix',
'/(vert|ind)ices$/i' => '\1ex',
'/^(ox)en/i' => '\1',
'/(alias)(es)*$/i' => '\1',
'/(alumn|bacill|cact|foc|fung|nucle|radi|stimul|syllab|termin|viri?)i$/i' => '\1us',
'/([ftw]ax)es/i' => '\1',
'/(cris|ax|test)es$/i' => '\1is',
'/(shoe|slave)s$/i' => '\1',
'/(o)es$/i' => '\1',
'/ouses$/' => 'ouse',
'/([^a])uses$/' => '\1us',
'/([m|l])ice$/i' => '\1ouse',
'/(x|ch|ss|sh)es$/i' => '\1',
'/(m)ovies$/i' => '\1\2ovie',
'/(s)eries$/i' => '\1\2eries',
'/([^aeiouy]|qu)ies$/i' => '\1y',
'/([lr])ves$/i' => '\1f',
'/(tive)s$/i' => '\1',
'/(hive)s$/i' => '\1',
'/(drive)s$/i' => '\1',
'/([^fo])ves$/i' => '\1fe',
'/(^analy)ses$/i' => '\1sis',
'/(analy|diagno|^ba|(p)arenthe|(p)rogno|(s)ynop|(t)he)ses$/i' => '\1\2sis',
'/([ti])a$/i' => '\1um',
'/(p)eople$/i' => '\1\2erson',
'/(m)en$/i' => '\1an',
'/(c)hildren$/i' => '\1\2hild',
'/(n)ews$/i' => '\1\2ews',
'/(n)etherlands$/i' => '\1\2etherlands',
'/eaus$/' => 'eau',
'/^(.*us)$/' => '\\1',
'/s$/i' => '',
];
/**
* @var array the special rules for converting a word between its plural form and singular form.
* The keys are the special words in singular form, and the values are the corresponding plural form.
*/
public static $specials = [
'atlas' => 'atlases',
'beef' => 'beefs',
'brother' => 'brothers',
'cafe' => 'cafes',
'child' => 'children',
'cookie' => 'cookies',
'corpus' => 'corpuses',
'cow' => 'cows',
'curve' => 'curves',
'foe' => 'foes',
'ganglion' => 'ganglions',
'genie' => 'genies',
'genus' => 'genera',
'graffito' => 'graffiti',
'hoof' => 'hoofs',
'loaf' => 'loaves',
'man' => 'men',
'money' => 'monies',
'mongoose' => 'mongooses',
'move' => 'moves',
'mythos' => 'mythoi',
'niche' => 'niches',
'numen' => 'numina',
'occiput' => 'occiputs',
'octopus' => 'octopuses',
'opus' => 'opuses',
'ox' => 'oxen',
'penis' => 'penises',
'sex' => 'sexes',
'soliloquy' => 'soliloquies',
'testis' => 'testes',
'trilby' => 'trilbys',
'turf' => 'turfs',
'wave' => 'waves',
'Amoyese' => 'Amoyese',
'bison' => 'bison',
'Borghese' => 'Borghese',
'bream' => 'bream',
'breeches' => 'breeches',
'britches' => 'britches',
'buffalo' => 'buffalo',
'cantus' => 'cantus',
'carp' => 'carp',
'chassis' => 'chassis',
'clippers' => 'clippers',
'cod' => 'cod',
'coitus' => 'coitus',
'Congoese' => 'Congoese',
'contretemps' => 'contretemps',
'corps' => 'corps',
'debris' => 'debris',
'diabetes' => 'diabetes',
'djinn' => 'djinn',
'eland' => 'eland',
'elk' => 'elk',
'equipment' => 'equipment',
'Faroese' => 'Faroese',
'flounder' => 'flounder',
'Foochowese' => 'Foochowese',
'gallows' => 'gallows',
'Genevese' => 'Genevese',
'Genoese' => 'Genoese',
'Gilbertese' => 'Gilbertese',
'graffiti' => 'graffiti',
'headquarters' => 'headquarters',
'herpes' => 'herpes',
'hijinks' => 'hijinks',
'Hottentotese' => 'Hottentotese',
'information' => 'information',
'innings' => 'innings',
'jackanapes' => 'jackanapes',
'Kiplingese' => 'Kiplingese',
'Kongoese' => 'Kongoese',
'Lucchese' => 'Lucchese',
'mackerel' => 'mackerel',
'Maltese' => 'Maltese',
'mews' => 'mews',
'moose' => 'moose',
'mumps' => 'mumps',
'Nankingese' => 'Nankingese',
'news' => 'news',
'nexus' => 'nexus',
'Niasese' => 'Niasese',
'Pekingese' => 'Pekingese',
'Piedmontese' => 'Piedmontese',
'pincers' => 'pincers',
'Pistoiese' => 'Pistoiese',
'pliers' => 'pliers',
'Portuguese' => 'Portuguese',
'proceedings' => 'proceedings',
'rabies' => 'rabies',
'rice' => 'rice',
'rhinoceros' => 'rhinoceros',
'salmon' => 'salmon',
'Sarawakese' => 'Sarawakese',
'scissors' => 'scissors',
'series' => 'series',
'Shavese' => 'Shavese',
'shears' => 'shears',
'siemens' => 'siemens',
'species' => 'species',
'swine' => 'swine',
'testes' => 'testes',
'trousers' => 'trousers',
'trout' => 'trout',
'tuna' => 'tuna',
'Vermontese' => 'Vermontese',
'Wenchowese' => 'Wenchowese',
'whiting' => 'whiting',
'wildebeest' => 'wildebeest',
'Yengeese' => 'Yengeese',
];
/**
* @var array fallback map for transliteration used by [[transliterate()]] when intl isn't available.
*/
public static $transliteration = [
'À' => 'A', 'Á' => 'A', 'Â' => 'A', 'Ã' => 'A', 'Ä' => 'A', 'Å' => 'A', 'Æ' => 'AE', 'Ç' => 'C',
'È' => 'E', 'É' => 'E', 'Ê' => 'E', 'Ë' => 'E', 'Ì' => 'I', 'Í' => 'I', 'Î' => 'I', 'Ï' => 'I',
'Ð' => 'D', 'Ñ' => 'N', 'Ò' => 'O', 'Ó' => 'O', 'Ô' => 'O', 'Õ' => 'O', 'Ö' => 'O', 'Ő' => 'O',
'Ø' => 'O', 'Ù' => 'U', 'Ú' => 'U', 'Û' => 'U', 'Ü' => 'U', 'Ű' => 'U', 'Ý' => 'Y', 'Þ' => 'TH',
'ß' => 'ss',
'à' => 'a', 'á' => 'a', 'â' => 'a', 'ã' => 'a', 'ä' => 'a', 'å' => 'a', 'æ' => 'ae', 'ç' => 'c',
'è' => 'e', 'é' => 'e', 'ê' => 'e', 'ë' => 'e', 'ì' => 'i', 'í' => 'i', 'î' => 'i', 'ï' => 'i',
'ð' => 'd', 'ñ' => 'n', 'ò' => 'o', 'ó' => 'o', 'ô' => 'o', 'õ' => 'o', 'ö' => 'o', 'ő' => 'o',
'ø' => 'o', 'ù' => 'u', 'ú' => 'u', 'û' => 'u', 'ü' => 'u', 'ű' => 'u', 'ý' => 'y', 'þ' => 'th',
'ÿ' => 'y',
];
/**
* Shortcut for `Any-Latin; NFKD` transliteration rule. The rule is strict, letters will be transliterated with
* the closest sound-representation chars. The result may contain any UTF-8 chars. For example:
* `获取到 どちら Українська: ґ,є, Српска: ђ, њ, џ! ¿Español?` will be transliterated to
* `huò qǔ dào dochira Ukraí̈nsʹka: g̀,ê, Srpska: đ, n̂, d̂! ¿Español?`
*
* Used in [[transliterate()]].
* For detailed information see [unicode normalization forms](http://unicode.org/reports/tr15/#Normalization_Forms_Table)
* @see http://unicode.org/reports/tr15/#Normalization_Forms_Table
* @see transliterate()
* @since 2.0.7
*/
const TRANSLITERATE_STRICT = 'Any-Latin; NFKD';
/**
* Shortcut for `Any-Latin; Latin-ASCII` transliteration rule. The rule is medium, letters will be
* transliterated to characters of Latin-1 (ISO 8859-1) ASCII table. For example:
* `获取到 どちら Українська: ґ,є, Српска: ђ, њ, џ! ¿Español?` will be transliterated to
* `huo qu dao dochira Ukrainsʹka: g,e, Srpska: d, n, d! ¿Espanol?`
*
* Used in [[transliterate()]].
* For detailed information see [unicode normalization forms](http://unicode.org/reports/tr15/#Normalization_Forms_Table)
* @see http://unicode.org/reports/tr15/#Normalization_Forms_Table
* @see transliterate()
* @since 2.0.7
*/
const TRANSLITERATE_MEDIUM = 'Any-Latin; Latin-ASCII';
/**
* Shortcut for `Any-Latin; Latin-ASCII; [\u0080-\uffff] remove` transliteration rule. The rule is loose,
* letters will be transliterated with the characters of Basic Latin Unicode Block.
* For example:
* `获取到 どちら Українська: ґ,є, Српска: ђ, њ, џ! ¿Español?` will be transliterated to
* `huo qu dao dochira Ukrainska: g,e, Srpska: d, n, d! Espanol?`
*
* Used in [[transliterate()]].
* For detailed information see [unicode normalization forms](http://unicode.org/reports/tr15/#Normalization_Forms_Table)
* @see http://unicode.org/reports/tr15/#Normalization_Forms_Table
* @see transliterate()
* @since 2.0.7
*/
const TRANSLITERATE_LOOSE = 'Any-Latin; Latin-ASCII; [\u0080-\uffff] remove';
/**
* @var mixed Either a [[\Transliterator]], or a string from which a [[\Transliterator]] can be built
* for transliteration. Used by [[transliterate()]] when intl is available. Defaults to [[TRANSLITERATE_LOOSE]]
* @see http://php.net/manual/en/transliterator.transliterate.php
*/
public static $transliterator = self::TRANSLITERATE_LOOSE;
/**
* Converts a word to its plural form.
* Note that this is for English only!
* For example, 'apple' will become 'apples', and 'child' will become 'children'.
* @param string $word the word to be pluralized
* @return string the pluralized word
*/
public static function pluralize($word)
{
if (isset(static::$specials[$word])) {
return static::$specials[$word];
}
foreach (static::$plurals as $rule => $replacement) {
if (preg_match($rule, $word)) {
return preg_replace($rule, $replacement, $word);
}
}
return $word;
}
/**
* Returns the singular of the $word
* @param string $word the english word to singularize
* @return string Singular noun.
*/
public static function singularize($word)
{
$result = array_search($word, static::$specials, true);
if ($result !== false) {
return $result;
}
foreach (static::$singulars as $rule => $replacement) {
if (preg_match($rule, $word)) {
return preg_replace($rule, $replacement, $word);
}
}
return $word;
}
/**
* Converts an underscored or CamelCase word into a English
* sentence.
* @param string $words
* @param boolean $ucAll whether to set all words to uppercase
* @return string
*/
public static function titleize($words, $ucAll = false)
{
$words = static::humanize(static::underscore($words), $ucAll);
return $ucAll ? ucwords($words) : ucfirst($words);
}
/**
* Returns given word as CamelCased
* Converts a word like "send_email" to "SendEmail". It
* will remove non alphanumeric character from the word, so
* "who's online" will be converted to "WhoSOnline"
* @see variablize()
* @param string $word the word to CamelCase
* @return string
*/
public static function camelize($word)
{
return str_replace(' ', '', ucwords(preg_replace('/[^A-Za-z0-9]+/', ' ', $word)));
}
/**
* Converts a CamelCase name into space-separated words.
* For example, 'PostTag' will be converted to 'Post Tag'.
* @param string $name the string to be converted
* @param boolean $ucwords whether to capitalize the first letter in each word
* @return string the resulting words
*/
public static function camel2words($name, $ucwords = true)
{
$label = trim(strtolower(str_replace([
'-',
'_',
'.'
], ' ', preg_replace('/(?<![A-Z])[A-Z]/', ' \0', $name))));
return $ucwords ? ucwords($label) : $label;
}
/**
* Converts a CamelCase name into an ID in lowercase.
* Words in the ID may be concatenated using the specified character (defaults to '-').
* For example, 'PostTag' will be converted to 'post-tag'.
* @param string $name the string to be converted
* @param string $separator the character used to concatenate the words in the ID
* @param boolean|string $strict whether to insert a separator between two consecutive uppercase chars, defaults to false
* @return string the resulting ID
*/
public static function camel2id($name, $separator = '-', $strict = false)
{
$regex = $strict ? '/[A-Z]/' : '/(?<![A-Z])[A-Z]/';
if ($separator === '_') {
return trim(strtolower(preg_replace($regex, '_\0', $name)), '_');
} else {
return trim(strtolower(str_replace('_', $separator, preg_replace($regex, $separator . '\0', $name))), $separator);
}
}
/**
* Converts an ID into a CamelCase name.
* Words in the ID separated by `$separator` (defaults to '-') will be concatenated into a CamelCase name.
* For example, 'post-tag' is converted to 'PostTag'.
* @param string $id the ID to be converted
* @param string $separator the character used to separate the words in the ID
* @return string the resulting CamelCase name
*/
public static function id2camel($id, $separator = '-')
{
return str_replace(' ', '', ucwords(implode(' ', explode($separator, $id))));
}
/**
* Converts any "CamelCased" into an "underscored_word".
* @param string $words the word(s) to underscore
* @return string
*/
public static function underscore($words)
{
return strtolower(preg_replace('/(?<=\\w)([A-Z])/', '_\\1', $words));
}
/**
* Returns a human-readable string from $word
* @param string $word the string to humanize
* @param boolean $ucAll whether to set all words to uppercase or not
* @return string
*/
public static function humanize($word, $ucAll = false)
{
$word = str_replace('_', ' ', preg_replace('/_id$/', '', $word));
return $ucAll ? ucwords($word) : ucfirst($word);
}
/**
* Same as camelize but first char is in lowercase.
* Converts a word like "send_email" to "sendEmail". It
* will remove non alphanumeric character from the word, so
* "who's online" will be converted to "whoSOnline"
* @param string $word to lowerCamelCase
* @return string
*/
public static function variablize($word)
{
$word = static::camelize($word);
return strtolower($word[0]) . substr($word, 1);
}
/**
* Converts a class name to its table name (pluralized)
* naming conventions. For example, converts "Person" to "people"
* @param string $className the class name for getting related table_name
* @return string
*/
public static function tableize($className)
{
return static::pluralize(static::underscore($className));
}
/**
* Returns a string with all spaces converted to given replacement,
* non word characters removed and the rest of characters transliterated.
*
* If intl extension isn't available uses fallback that converts latin characters only
* and removes the rest. You may customize characters map via $transliteration property
* of the helper.
*
* @param string $string An arbitrary string to convert
* @param string $replacement The replacement to use for spaces
* @param boolean $lowercase whether to return the string in lowercase or not. Defaults to `true`.
* @return string The converted string.
*/
public static function slug($string, $replacement = '-', $lowercase = true)
{
$string = static::transliterate($string);
$string = preg_replace('/[^a-zA-Z0-9=\s—–-]+/u', '', $string);
$string = preg_replace('/[=\s—–-]+/u', $replacement, $string);
$string = trim($string, $replacement);
return $lowercase ? strtolower($string) : $string;
}
/**
* Returns transliterated version of a string.
*
* If intl extension isn't available uses fallback that converts latin characters only
* and removes the rest. You may customize characters map via $transliteration property
* of the helper.
*
* @param string $string input string
* @param string|\Transliterator $transliterator either a [[Transliterator]] or a string
* from which a [[Transliterator]] can be built.
* @return string
* @since 2.0.7 this method is public.
*/
public static function transliterate($string, $transliterator = null)
{
if (static::hasIntl()) {
if ($transliterator === null) {
$transliterator = static::$transliterator;
}
return transliterator_transliterate($transliterator, $string);
} else {
return strtr($string, static::$transliteration);
}
}
/**
* @return boolean if intl extension is loaded
*/
protected static function hasIntl()
{
return extension_loaded('intl');
}
/**
* Converts a table name to its class name. For example, converts "people" to "Person"
* @param string $tableName
* @return string
*/
public static function classify($tableName)
{
return static::camelize(static::singularize($tableName));
}
/**
* Converts number to its ordinal English form. For example, converts 13 to 13th, 2 to 2nd ...
* @param integer $number the number to get its ordinal value
* @return string
*/
public static function ordinalize($number)
{
if (in_array($number % 100, range(11, 13))) {
return $number . 'th';
}
switch ($number % 10) {
case 1:
return $number . 'st';
case 2:
return $number . 'nd';
case 3:
return $number . 'rd';
default:
return $number . 'th';
}
}
/**
* Converts a list of words into a sentence.
*
* Special treatment is done for the last few words. For example,
*
* ```php
* $words = ['Spain', 'France'];
* echo Inflector::sentence($words);
* // output: Spain and France
*
* $words = ['Spain', 'France', 'Italy'];
* echo Inflector::sentence($words);
* // output: Spain, France and Italy
*
* $words = ['Spain', 'France', 'Italy'];
* echo Inflector::sentence($words, ' & ');
* // output: Spain, France & Italy
* ```
*
* @param array $words the words to be converted into an string
* @param string $twoWordsConnector the string connecting words when there are only two
* @param string $lastWordConnector the string connecting the last two words. If this is null, it will
* take the value of `$twoWordsConnector`.
* @param string $connector the string connecting words other than those connected by
* $lastWordConnector and $twoWordsConnector
* @return string the generated sentence
* @since 2.0.1
*/
public static function sentence(array $words, $twoWordsConnector = ' and ', $lastWordConnector = null, $connector = ', ')
{
if ($lastWordConnector === null) {
$lastWordConnector = $twoWordsConnector;
}
switch (count($words)) {
case 0:
return '';
case 1:
return reset($words);
case 2:
return implode($twoWordsConnector, $words);
default:
return implode($connector, array_slice($words, 0, -1)) . $lastWordConnector . end($words);
}
}
}
There is some example.
echo "Inflector Test";
require('PhInflector.php');
echo "<hr>";
echo PhInflector::slug('Höäpeäöäich Médsui27:;;,.1! *"29p');
echo "<hr>";
echo PhInflector::slug('HIJO"$(/&T §!"(/&T"§:;;,.1! *"29p');
echo "<hr>";
echo PhInflector::slug('38917 jiodj d ! *"29p');
echo "<hr>";
echo PhInflector::slug('каи циефле ///!!!');
And forward github link click here.
I'm sure you can google to find plenty of libs that do this.
But if you feel like coding, you could try the reverse process: start with singular words of dictionary (download free ones, used by aspell or whatever), use pluralization rule; collect mappings and switch the direction. For "type" you would pluralize to "types", and reverse mapping would work as expected. While there are exceptions here too it is slightly easier to reliably pluralize things. I did this a while back (in mid 90s... :-) ), for an online game (a MUD), where descriptions for multiple identical items were concatenatd, and automatic pluralization was needed.
Also: given that it's finite number of tables you could just use simplest algorithm, get raw output, eyeball it and fix error cases manually. :-)
I think you have to use a list to translate plural into singular for some special words (in your example Types->Type).
I think you could have a look at the sourcecode of CakePHP (you might start your search here). They are using such an algorithm for their tablenames and fieldnames to automagically join tables.
[Edit:] Here you have some scientific work to read about "Plural inflection in English"
I'm going to try this MorphAdorner: http://morphadorner.northwestern.edu/morphadorner/download/ (Java). It's a collection of different types of NLP processing tools, and you can test them through online examples. For your problem (that is also my problem) there's the Pluralizer tool: http://morphadorner.northwestern.edu/morphadorner/pluralizer/example/
Consider the python package "inflect"
"Correctly generate plurals, singular nouns, ordinals, indefinite articles; convert numbers to words"
https://pypi.python.org/pypi/inflect
I just encounter this problem and developed a solution in 10 mins.
I think @paxdiablo provides a good thought on building a transforming engine and add rules. I build one dictionary rule and three common rules. The dictionary rule goes to a dict file to lookup exception cases, while the three common rules handle "ies", "es" and "s" respectively.
However, it may takes too much time to add all exceptions to the dictionary, e.g., pies/trees/bus etc. One improvement I have made to deal with these words is to make sure it can be converted back.
E.g., if we incorrectly apply the remove "es" rule to "trees" and convert it to "tre", when trying to add plural form back, you will get "tres", which doesn't equal to the original "tree" and you know the "es" rule should not be applied. This method can solve exceptions mentioned above without adding them to a dictionary file.
I end up with a dictionary file of 42 truly exceptional words and it could handle most of the cases.
There's a nice implementation of an inflector in uNnAddIns project that even implements an experimental spanish inflector. The idea is caught from Rails Inflector module.
It can be used as well for other things like converting from CamelCase to normal text and other goodies and for example generating browser friendly URLs from titles.
{var%20f='http://v.t.sina.com.cn/share/share.php?appkey=1515056452',u=z||d.location,p=['&url=',e(u),'&title=',e(t||d.title),'&source=',e(r),'&sourceUrl=',e(l),'&content=',c||'gb2312','&pic=',e(p||'')].join('');function%20a(){if(!window.open([f,p].join(''),'mb',['toolbar=0,status=0,resizable=1,width=440,height=430,left=',(s.width-440)/2,',top=',(s.height-430)/2].join('')))u.href=[f,p].join('');};if(/Firefox/.test(navigator.userAgent))setTimeout(a,0);else%20a();})(screen,document,encodeURIComponent,'','','https://img.manongdao.com/sparkler-677774__340.jpg', '推荐 贼婆χ 的文章《How to turn plural words singular?》','https://www.manongdao.com/article-539839.html','页面编码gb2312|utf-8默认gb2312'));){kind=link}