How do I coalesce a sequence of identical characters into just one?

Suppose I have this:

My---sun--is------very-big---.

I want to replace all multiple hyphens with just one hyphen.

import re

astr='My---sun--is------very-big---.'

print(re.sub('-+','-',astr))
# My-sun-is-very-big-.

If you want to replace any run of consecutive characters, you can use

>>> import re
>>> a = "AA---BC++++DDDD-EE$$$$FF"
>>> print(re.sub(r"(.)\1+",r"\1",a))
A-BC+D-E$F

If you only want to coalesce non-word-characters, use

>>> print(re.sub(r"(\W)\1+",r"\1",a))
AA-BC+DDDD-EE$FF

If it's really just hyphens, I recommend unutbu's solution.

If you really only want to coalesce hyphens, use the other suggestions. Otherwise you can write your own function, something like this:

>>> def coalesce(x):
...     n = []
...     for c in x:
...         if not n or c != n[-1]:
...             n.append(c)
...     return ''.join(n)
...
>>> coalesce('My---sun--is------very-big---.')
'My-sun-is-very-big-.'
>>> coalesce('aaabbbccc')
'abc'

As usual, there's a nice itertools solution, using groupby:

>>> from itertools import groupby
>>> s = 'aaaaa----bbb-----cccc----d-d-d'
>>> ''.join(key for key, group in groupby(s))
'a-b-c-d-d-d'

How about:

>>> import re
>>> re.sub("-+", "-", "My---sun--is------very-big---.")
'My-sun-is-very-big-.'

the regular expression "-+" will look for 1 or more "-".

re.sub('-+', '-', "My---sun--is------very-big---")

How about an alternate without the re module:

'-'.join(filter(lambda w: len(w) > 0, 'My---sun--is------very-big---.'.split("-")))

Or going with Tim and FogleBird's previous suggestion, here's a more general method:

def coalesce_factory(x):
    return lambda sent: x.join(filter(lambda w: len(w) > 0, sent.split(x)))

hyphen_coalesce = coalesce_factory("-")
hyphen_coalesce('My---sun--is------very-big---.')

Though personally, I would use the re module first :)

• mcpeterson

Another simple solution is the String object's replace function.

while '--' in astr:
    astr = astr.replace('--','-')

if you don't want to use regular expressions:

    my_string = my_string.split('-')
    my_string = filter(None, my_string)
    my_string = '-'.join(my_string)

I have

my_str = 'a, b,,,,, c, , , d'

I want

'a,b,c,d'

compress all the blanks (the "replace" bit), then split on the comma, then if not None join with a comma in between:

my_str_2 = ','.join([i for i in my_str.replace(" ", "").split(',') if i])