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I want to split a python string line = '1 -1 2 3 -1 4' so that my output is a python list['1','2','3','4']. I tried solution given here and here. However, some strange output is coming. My code:

line = '1 -1 2 3 -1 4'
import re    
t=re.split("-1| ", line)

output:

['1', '', '', '2', '3', '', '', '4']

Any help is appreciated!

Community
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CKM
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6 Answers6

4

That was a tricky one :)

re.split(r"(?:\s-1)?\s",line)
#['1', '2', '3', '4']

And the fastest solution (runs about 4.5 times faster than the regex):

line.replace("-1 ", "").split()
DYZ
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1

Try: 

t=re.split("\s+",line.replace("-1"," "))
Amorpheuses
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  • I had that sol is mind. How about time complexity of the above code or Can we do that without replacing -1 by space? – CKM Feb 07 '17 at 05:22
  • Yes I would imagine it's not the most efficient of possible solutions. Would have to do some timing tests. – Amorpheuses Feb 07 '17 at 05:27
  • The replace with space appears to be consistently faster by 3-4 times - but the reader should probably do his/her own timing tests to confirm. – Amorpheuses Feb 07 '17 at 05:50
0

You can try this too with lookahead:

print re.findall('(?<=[^-])\d+', ' ' +line)
# ['1', '2', '3', '4']

This is more generic since this will filter out all negative numbers.

line = '-10 12 -10 20 3 -2 40 -5 5 -1 1' 
print re.findall('(?<=[^-\d])\d+', ' ' +line)
# ['12', '20', '3', '40', '5', '1']
Sandipan Dey
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0

I'm not using a regex but a conditional list comprehension:

>>> line = '1 -1 2 3 -1 4'
>>> [substr for substr in line.split() if not substr.startswith('-')]
['1', '2', '3', '4']
MSeifert
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   line.replace(' -1','').split(' ')
   # ['1','2','3','4'].
Sandip
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-1

I can't say whether this would be more efficient than some of the other solutions, but a list comprehension is very readable and could certainly do the trick:

line = '1 -1 2 3 -1 4'
t = [str(item) for item in line.split(" ") if int(item) >= 0]
>>> ['1', '2', '3', '4']
Zach Ward
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