I would like to remove all characters from a first string s1 exactly the number of times they appear in another string s2, i.e. if s1 = "AAABBBCCCCCCD" and s2 = "ABBCCC" then the result should be s = "AABCCCD". (The order of the characters in the resulting string is actually irrelevant but it's a plus if it can be preserved.)
The following rather crude code can do this:
def reduce_string(s1, s2):
s = s1
for c in s2:
if c in s:
s = s.replace(c, "", 1)
return(s)
# examples
reduce_string("AAABBBCCCCCCD", "ABBCCC")
reduce_string("AAABBBCCCCCCD", "ABBCCCE")
My question is, can the same be achieved by clever use of some built-in function or at least in a more elegant way? Thank you for all your answers!
You can use counter objects. Subtract one against the other and join the remaining elements together.
from collections import Counter
s1 = "AAABBBCCCCCCD"
s2 = "ABBCCC"
counter = Counter(s1)
counter.subtract(Counter(s2))
result = ''.join(counter.elements())
print(result)
AABCCCD
As a one-liner:
print(''.join((Counter(s1) - Counter(s2)).elements()))
There is a filterfalse function in itertools module that you should see.
Consult the documentation here.
The filterfalse function returns elements from a iterable when the predicate is evaluated as False.
So, one possible solution might be:
import itertools
def reduce_string(s1, s2):
def predicate(letter, param=list(s2)):
if letter in param:
param.remove(letter)
return True
return False
result = itertools.filterfalse(predicate, s1)
return ''.join(result)
reduce_string("AAABBBCCCCCCD", "ABBCCC")
reduce_string("AAABBBCCCCCCD", "ABBCCCE")
However, notice how my predicate function is a little trickier when it changes the second string.
The keyword argument param is evaluated when the function predicate is created inside the reduce_string scope as a list object.
Since the reference does not change but the elements inside param, I was able to change the second string for comparisons reasons.
Now, the question remains: is there a more elegant way to define predicate function?