CODEWITHSUNDEEP
pythonregex
Sam
Sam

Reputation: 2605

Regex to get rid of the last term with conditions

I would like to write a regex to remove the last character from a string, if the character is a (s).

However in doing so I would like to retain the (s) if it is preceded by another (s).

Example.

The output of Apples should be Apple.
The output of Process should be Process.

I need a regex that would capture the whole term if the expression is matched but would perform the replacement for a partial match.

I have used s$ to get rid of the last character.

Upvotes: 1

Views: 121

Answers (3)

Javier Buzzi
Javier Buzzi

Reputation: 6808

This has been talked about WAY too many times, and the consensus is always: its WAY too complicated to be handled through a simple regex. All of the solutions fail with these examples:

apples
carrots
process
processes
tennis

A solution is to use morpha:

git clone https://github.com/knowitall/morpha
cd morpha/
flex -i -Cfea -8 -omorpha.yy.c morpha.lex
gcc -o morpha morpha.yy.c
curl -s https://raw.githubusercontent.com/jhlau/predom_sense/master/lemmatiser_tools/morpha/verbstem.list > verbstem.list

now to test:

cat test.txt | ./morpha -c
apple
carrot
process
process
tennis

If you want a python solution, i suggest you go with nltk.

virtualenv env-nltk
source env-nltk/bin/activate
pip install nltk
python -c "import nltk; nltk.download()" # <- just get the whole thing, click "all" and then "download" on the "collections" tab

Now that everything is downloaded, lets fire off python and play with it.

>>> from nltk.stem.wordnet import WordNetLemmatizer
>>> lmtzr = WordNetLemmatizer()
>>> lmtzr.lemmatize('apples')
u'apple'
>>> lmtzr.lemmatize('tennis')
'tennis'
>>> lmtzr.lemmatize('process')
'process'
>>> lmtzr.lemmatize('processes')
u'process'

Upvotes: 4

riteshtch
riteshtch

Reputation: 8769

You could use negative lookbehind assertion to ensure substitution happens only if s is not preceded by another s.

>>> import re
>>> re.sub(r'(?<!s)s$', '', 'Apples')
'Apple'
>>> re.sub(r'(?<!s)s$', '', 'Process')
'Process'

Upvotes: 0

anubhava
anubhava

Reputation: 785128

You can use this negative lookbehind assertion:

(?<!s)s$

RegEx Demo

Breakup:

(?<!s)  # assert previous position doesn't have 's'
s       # match 's'
$       # assert end of line

Upvotes: 2

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