how to split a string at positions before a character?
- split a string before 'a'
- input: "fffagggahhh"
- output: ["fff", "aggg", "ahhh"]
the obvious way doesn't work:
>>> h=re.compile("(?=a)")
>>> h.split("fffagggahhh")
['fffagggahhh']
>>>
7 Answers
Ok, not exactly the solution you want but I thought it will be a useful addition to problem here.
Solution without re
Without re:
>>> x = "fffagggahhh"
>>> k = x.split('a')
>>> j = [k[0]] + ['a'+l for l in k[1:]]
>>> j
['fff', 'aggg', 'ahhh']
>>>
>>> rx = re.compile("(?:a|^)[^a]*")
>>> rx.findall("fffagggahhh")
['fff', 'aggg', 'ahhh']
>>> rx.findall("aaa")
['a', 'a', 'a']
>>> rx.findall("fgh")
['fgh']
>>> rx.findall("")
['']
1 Comment
John Machin
-1
re.findall("(?:^|a)[^a]*", "aaa") produces ['', 'a', 'a']>>> r=re.compile("(a?[^a]+)")
>>> r.findall("fffagggahhh")
['fff', 'aggg', 'ahhh']
EDIT:
This won't handle correctly double as in the string:
>>> r.findall("fffagggaahhh")
['fff', 'aggg', 'ahhh']
KennyTM's re seems better suited.
2 Comments
Jeff Mercado
I wonder if the OP would want to keep the empty string from the split if it started with an 'a'.
John Machin
-1 Uncool. Fails on repeated a's ... e.g. "aaa" -> empty list
import re
def split_before(pattern,text):
prev = 0
for m in re.finditer(pattern,text):
yield text[prev:m.start()]
prev = m.start()
yield text[prev:]
if __name__ == '__main__':
print list(split_before("a","fffagggahhh"))
re.split treats the pattern as a delimiter.
>>> print list(split_before("a","afffagggahhhaab"))
['', 'afff', 'aggg', 'ahhh', 'a', 'ab']
>>> print list(split_before("a","ffaabcaaa"))
['ff', 'a', 'abc', 'a', 'a', 'a']
>>> print list(split_before("a","aaaaa"))
['', 'a', 'a', 'a', 'a', 'a']
>>> print list(split_before("a","bbbb"))
['bbbb']
>>> print list(split_before("a",""))
['']
Comments
This one works on repeated a's
>>> re.findall("a[^a]*|^[^a]*", "aaaaa")
['a', 'a', 'a', 'a', 'a']
>>> re.findall("a[^a]*|[^a]+", "ffaabcaaa")
['ff', 'a', 'abc', 'a', 'a', 'a']
Approach: the main chunks that you are looking for are an a followed by zero or more not-a. That covers all possibilities except for zero or more not-a. That can happen only at the start of the input string.
Comments
>>> foo = "abbcaaaabbbbcaaab"
>>> bar = foo.split("c")
>>> baz = [bar[0]] + ["c"+x for x in bar[1:]]
>>> baz
['abb', 'caaaabbbb', 'caaab']
Due to how slicing works, this will work properly even if there are no occurrences of c in foo.
Comments
split() takes an argument for the character to split on:
>>> "fffagggahhh".split('a')
['fff', 'ggg', 'hhh']
Comments
"aaa"—['', 'a', 'a', 'a']or['a', 'a', 'a']?