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[搜索]波特词干（Porter Streamming）提取算法详解（2）
下面分为5大步骤来使用前面提到的替换条件来进行词干提取。
左边是规则，右边是提取成功或者失败的例子（用小写字母表示）。
步骤1
SSES -> SS caresses -> caress
IES -> I ponies -> poni
ties -> ti
SS -> SS caress -> caress
S -> cats -> cat
(m>0) EED -> EE feed -> feed
agreed -> agree
(*v*) ED -> plastered -> plaster
bled -> bled
(*v*) ING -> motoring -> motor
sing -> sing
AT -> ATE conflat(ed) -> conflate
BL -> BLE troubl(ed) -> trouble
IZ -> IZE siz(ed) -> size
(*d and not (*L or *S or *Z))
-> single letter
hopp(ing) -> hop
tann(ed) -> tan
fall(ing) -> fall
hiss(ing) -> hiss
fizz(ed) -> fizz
(m=1 and *o) -> E fail(ing) -> fail
fil(ing) -> file
(*v*) Y -> I happy -> happi
sky -> sky
通过步骤1的处理，复数和过去分词就被处理了。
步骤2
(m>0) ATIONAL -> ATE relational -> relate
(m>0) TIONAL -> TION conditional -> condition
rational -> rational
(m>0) ENCI -> ENCE valenci -> valence
(m>0) ANCI -> ANCE hesitanci -> hesitance
(m>0) IZER -> IZE digitizer -> digitize
(m>0) ABLI -> ABLE conformabli -> conformable
(m>0) ALLI -> AL radicalli -> radical
(m>0) ENTLI -> ENT differentli -> different
(m>0) ELI -> E vileli - > vile
(m>0) OUSLI -> OUS analogousli -> analogous
(m>0) IZATION -> IZE vietnamization -> vietnamize
(m>0) ATION -> ATE predication -> predicate
(m>0) ATOR -> ATE operator -> operate
(m>0) ALISM -> AL feudalism -> feudal
(m>0) IVENESS -> IVE decisiveness -> decisive
(m>0) FULNESS -> FUL hopefulness -> hopeful
(m>0) OUSNESS -> OUS callousness -> callous
(m>0) ALITI -> AL formaliti -> formal
(m>0) IVITI -> IVE sensitiviti -> sensitive
(m>0) BILITI -> BLE sensibiliti -> sensible
步骤3
(m>0) ICATE -> IC triplicate -> triplic
(m>0) ATIVE -> formative -> form
(m>0) ALIZE -> AL formalize -> formal
(m>0) ICITI -> IC electriciti -> electric
(m>0) ICAL -> IC electrical -> electric
(m>0) FUL -> hopeful -> hope
(m>0) NESS -> goodness -> good
步骤4
(m>1) AL -> revival -> reviv
(m>1) ANCE -> allowance -> allow
(m>1) ENCE -> inference -> infer
(m>1) ER -> airliner -> airlin
(m>1) IC -> gyroscopic -> gyroscop
(m>1) ABLE -> adjustable -> adjust
(m>1) IBLE -> defensible -> defens
(m>1) ANT -> irritant -> irrit
(m>1) EMENT -> replacement -> replac
(m>1) MENT -> adjustment -> adjust
(m>1) ENT -> dependent -> depend
(m>1 and (*S or *T)) ION -> adoption -> adopt
(m>1) OU -> homologou -> homolog
(m>1) ISM -> communism -> commun
(m>1) ATE -> activate -> activ
(m>1) ITI -> angulariti -> angular
(m>1) OUS -> homologous -> homolog
(m>1) IVE -> effective -> effect
(m>1) IZE -> bowdlerize -> bowdler
通过前面的四个步骤，后缀就被去掉了，剩下最后一步做一些微调操作。
步骤5
(m>1) E -> probate -> probat
rate -> rate
(m=1 and not *o) E -> cease -> ceas
(m > 1 and *d and *L) -> single letter
controll -> control
roll -> roll
有人专门对Porter的算法进行了测评，发现词干提取能显著提高召回率，而且轻度提取对准确率影响不大，但是深度提取会严重影响准确率，所以他们建议，首先使用轻度提取，如果查询结果太少时再使用深度提取。