Extract integers with specific length between separators

问题

Given a list of strings like:

L = ['1759@1@83@0#1362@0.2600@25.7400@2.8600#1094@1@129.6@14.4', 
     '1356@0.4950@26.7300@2.9700', 
     '1354@1.78@35.244@3.916#1101@2@40@0#1108@2@30@0',
     '1430@1@19.35@2.15#1431@3@245.62@60.29#1074@12@385.2@58.8#1109',
     '1809@8@75.34@292.66#1816@4@24.56@95.44#1076@47@510.89@1110.61']

I need to extract all integers with length 4 between separators # or @, and also extract the first and last integers. No floats.

My solution is a bit overcomplicated - replace with space and then applied this solution:

pat = r'(?<!\S)\d{4}(?!\S)'
out = [re.findall(pat, re.sub('[#@]', ' ', x)) for x in L]
print (out)
"""
[['1759', '1362', '1094'], 
 ['1356'], 
 ['1354', '1101', '1108'], 
 ['1430', '1431', '1074', '1109'], 
 ['1809', '1816', '1076']]
"""

Is it possible to change the regex for not using re.sub necessarily for replace? Is there another solution with better performance?

回答1:

To allow first and last occurrences that has no leading or trailing separator you could use negative lookarounds:

(?<![^#])\d{4}(?![^@])

(?<![^#]) is a near synonym for (?:^|#). The same applies for the negative lookahead.

See live demo here

回答2:

Interesting problem!

This can be easily tackled with the concepts of lookahead & lookbehind.

INPUT

pattern = "(?<!\.)(?<=[#@])\d{4}|(?<!\.)\d{4}(?=[@#])"
out = [re.findall(pattern, x) for x in L]
print (out)

OUTPUT

[['1759', '1362', '1094', '1234'],
 ['1356'],
 ['1354', '1101', '1108'],
 ['1430', '1431', '1074', '1109'],
 ['1809', '1816', '1076', '1110']]

EXPLANATION

The above pattern is a combination of two separate patterns separated by an | (OR operator).

pattern_1 = "(?<!\.)(?<=[#@])\d{4}"
\d{4}     --- Extract exactly 4 digits
(?<!\.)   --- The 4 digits must not be preceded by a period(.) NEGATIVE LOOKBEHIND
(?<=[#@]) --- The 4 digits must be preceded by a hashtag(#) or at(@) POSITIVE LOOKBEHIND

pattern_2 = "(?<!\.)\d{4}(?=[@#])"
\d{4}     --- Extract exactly 4 digits
(?<!\.)   --- The 4 digits must not be preceded by a period(.) NEGATIVE LOOKBEHIND
(?=[@#]   --- The 4 digits must be followed by a hashtag(#) or at(@) POSITIVE LOOKAHEAD

To better understand these concepts, click here

回答3:

Here is a complex list comprehension without using regex if you consider the integers of length 4 without the starting # or ending @ too :

[[n for o in p for n in o] for p in [[[m for m in k.split("@") if m.isdigit() and str(int(m))==m and len(m) ==4] for k in j.split("#")] for j in L]]

Output :

[['1759', '1362', '1094'], ['1356'], ['1354', '1101', '1108'], ['1430', '1431', '1074', '1109'], ['1809', '1816', '1076']]

来源：https://stackoverflow.com/questions/55096830/extract-integers-with-specific-length-between-separators

标签

python

regex

string

findall