What would be the most efficient way of inverting (i.e. multiplying with -1) the integers in the strings in a list using python?
Example input:
['-1 -2 -3 -4 -5 -6 -7 -8 9 -10 11',' -17 18 19 20 -21 22 -23 ',' -36 -37 -38 39 40 41 42 -43 44 ']
Desired output:
['1 2 3 4 5 6 7 8 -9 10 -11', '17 -18 -19 -20 21 -22 23', '36 37 38 -39 -40 -41 -42 43 -44']
Using simple list comprehensions
>>> lst = ['-1 -2 -3 -4 -5 -6 -7 -8 9 -10 11',' -17 18 19 20 -21 22 -23 ',' -36 -37 -38 39 40 41 42 -43 44 ']
>>> [' '.join(map(lambda x: str(-int(x)), s.split())) for s in lst]
['1 2 3 4 5 6 7 8 -9 10 -11', '17 -18 -19 -20 21 -22 23', '36 37 38 -39 -40 -41 -42 43 -44']
This does what you want. Hopefully the variable and function names make it relatively clear what's going on.
list_of_strings = ['-1 -2 -3 -4 -5 -6 -7 -8 9 -10 11',' -17 18 19 20 -21 22 -23 ',' -36 -37 -38 39 40 41 42 -43 44 ']
def process(string_of_ints):
return ' '.join( str(-int(each_word)) for each_word in string_of_ints.split() )
result = [ process(each_string) for each_string in list_of_strings ]
print(result)
It can be collapsed into one line at the cost of some clarity:
result = [ ' '.join( str(-int(each_word)) for each_word in each_string.split() ) for each_string in list_of_strings ]
(NB: "invert" is really a potentially misleading word - in mathematics, when used unqualified, the most common interpretation means do 1/x, not -x; in computing it might mean any one of a number of different things, including reversing the order of a sequence).
A slightly different approach then what has been posted so far
l=['-1 -2 -3 -4 -5 -6 -7 -8 9 -10 11',' -17 18 19 20 -21 22 -23 ',' -36 -37 -38 39 40 41 42 -43 44 ']
for i in xrange(len(l)):
tmp=[]
for s in l[i].split():
tmp.append(str(-int(s)))
l[i]=' '.join(tmp)
print l
['1 2 3 4 5 6 7 8 -9 10 -11', '17 -18 -19 -20 21 -22 23', '36 37 38 -39 -40 -41 -42 43 -44']
