Remove repeated letters in Python

Question

How do i remove repeated letters in a string?

Tried this without success..

def shorten_string(char_str):
    new=''
    for i in range(0,len(char_str)-1):
       if char_str[i-1] != char_str[i]:
           new += char_str[i]
return new

EDIT: Misunderstanding: i do not want to delete all repeated characthers. Just if they are repeated in order.

input: lloolleellaa
outpu: lolela

can you add sample output and input. – harshil9968 Dec 05 '16 at 14:09 — harshil9968, Dec 05 '16 at 14:09
@harshil9968 Check the first line of the post. – 001 Dec 05 '16 at 14:11 — 001, Dec 05 '16 at 14:11
See http://stackoverflow.com/a/9841401/3832970 – Wiktor Stribiżew Dec 05 '16 at 14:15 — Wiktor Stribiżew, Dec 05 '16 at 14:15

score 8 · Answer 1 · answered Dec 05 '16 at 14:12

8

It is the same logic as is for all languages. This is a frequent question asked in interviews. Basically you assign each character of the string to a data structure. The choice of the data structure differs from language and performance. Sometimes they might also ask if the order matters or not.

>>> foo = 'haalllooo'
>>> ''.join(sorted(set(foo), key=foo.index))
'halo'

answered Dec 05 '16 at 14:12

roymustang86

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See edit, I wrote the question in a bad way i guess. – Sander B Dec 05 '16 at 14:18
@SanderB Then the solution by Dan D. does what you need. – Keiwan Dec 05 '16 at 14:20
1

I upvoted this before I realized that it actually has a major bug that deletes **all** duplicated letters, not just the ones that are next to each other. By the time I realized the error, it was too late to take the upvote back. Beware this answer doesn't answer the question. – Barker May 05 '20 at 00:22
It worked for me too in the Roman Urdu case. Thanks – Bilal Chandio Oct 05 '20 at 19:48

Dan D. · Accepted Answer · 2016-12-05T14:23:13.343

Removing adjacent equal items can be done as follows with groupby:

>>> import itertools
>>> ''.join(c[0] for c in itertools.groupby('haalllooo'))
'halo'

This simply takes the heads of each of the groups of equal items.

>>> ''.join(c[0] for c in itertools.groupby('haalllooo thheeerrree tttthhhiiisss iiisss aaann eeeexxxaaammpppllleee'))
'halo there this is an example'

To keep only the unique items in order:

def unique(it):
    s = set()
    for x in it:
        if x not in s:
           s.add(x)
           yield x

This can be used like this:

>>> ''.join(unique('haalllooo'))
'halo'
>>> ''.join(unique('haalllooo thheeerrree tttthhhiiisss iiisss aaann eeeexxxaaammpppllleee'))
'halo terisnxmp'

You should consider adding this as an answer to the duplicate. A solution which only removes adjacent items isn't represented on that question yet. — Chris Mueller, Dec 05 '16 at 14:37

score 2 · Answer 3 · edited Feb 10 '19 at 13:49

2

My solution with regex:

>>> import re

>>> re.compile(r'(.)\1{1,}', re.IGNORECASE).sub(r'\1', "haalllooo thheeerrree tttthhhiiisss iiisss aaann eeeexxxaaammpppllleee")
'halo there this is an example'

But note that Dan's solution is 4x faster then regex!!

edited Feb 10 '19 at 13:49

Zoe

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answered Feb 10 '19 at 12:24

Thomas Decaux

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Remove repeated letters in Python

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