remove all sub-strings from a string

Question

I have a string from which I want to remove all possible combinations till the end. I tried this:

combinations = ['XY', 'ZU', 'YY']
lst_matched = list(filter(lambda val: val in mystring, combinations))
for i in matches:
    if len(mystring) > 0:
        mystring = mystring.replace(i,'')
        print('after', mystring)

If I use this with a mystring like ZXYUYY, it will identify lst_matched as [XY, YY] and my function will correctly remove these substrings from mystering.

However, after removing these substrings, the updated string now has ZUwhich is also another combination to check for.

How can I modify my code such that it searches for all possible combinations till there's no match left? Recurssion could be used but not sure how.

Answer 1

Try this:

def replace(mystring, combinations):
    val = next((val for val in combinations if val in mystring), None)
    while val is not None:
        mystring = mystring.replace(val, '')
        val = next((val for val in combinations if val in mystring), None)
    return mystring

Basically you find the first combination that can be found in mystring (this can be done with next((val for val in combinations if val in mystring), None)). If no such a combination can be found then val will be None.

Then you replace that specific combination with ''. And you repeat. You stop when such combination cannot be found anymore (i.e., when val is None).

Examples:

>>> replace('ZXYUYY', ['XY', 'ZU', 'YY'])
''
>>> replace('ZXYUYY', ['XY', 'YY'])
'ZU'
>>> replace('AZXYUYY', ['XY', 'ZU', 'YY'])
'A'
>>> replace('AZBXYUYY', ['XY', 'ZU', 'YY'])
'AZBU'

Answer 2

Just repeat the replacement until the resulting string is the same as the original string:

combinations = ['XY', 'YY', 'ZU']
mystring = 'ZXYUYY'
while True:
    new_string = mystring
    for combination in combinations:
        new_string = new_string.replace(combination, '')
    if new_string == mystring:
        break
    mystring = new_string
print(mystring)

Or more simply using a regular expression:

import re

regex = re.compile('XY|YY|ZU')
mystring = 'ZXYUYY'
while True:
    mystring, substitutions = regex.subn(mystring, '')
    if not substitutions:
        break
print(mystring)

Answer 3

You can loop over the permutations of your "combination":

from itertools import permutations
mystring = "ZXYUYY"
combinations = ['ZU', 'XY', 'YY']
for p in permutations(combinations, len(combinations)):
    for c in p:
        mystring = mystring.replace(c, "")
        print('after', mystring)
print(mystring)

Answer 4

Create an "infinite" loop that exits once the string has no occurrences of the strings from remove_list (i.e. your combinations list)

remove_list = ['XY', 'YY', 'ZU'] 

s = "ZXYUYY"
while True:
    if any(i in s for i in remove_list):
        for j in remove_list:
            s = s.replace(j, "")
    break
print(s)