How do I generate all possible pairs permutations from a list in Python?
Example:
input = [3, 8, 2]
output = ['3-8', '3-2', '8-3', '8-2', '2-3', '2-8']
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Welcome to SO. This is not a free code-writing service, hence your question is supposed to present your own attempts. Moreover, this question is a duplicate.Eli Korvigo– Eli Korvigo2017-12-07 15:03:37 +00:00Commented Dec 7, 2017 at 15:03
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4 Answers
You can use itertools.permutations:
import itertools
input = [3, 8, 2]
final_list = ["{}-{}".format(*i) for i in itertools.permutations(input, 2)]
Output:
['3-8', '3-2', '8-3', '8-2', '2-3', '2-8']
However, if you want all operations up-to and including the length of the list, you can try this:
final_list = list(itertools.chain(*[['-'.join(["{}"]*b).format(*i) for i in itertools.permutations(input, b)] for b in range(2, len(input)+1)]))
Output:
['3-8', '3-2', '8-3', '8-2', '2-3', '2-8', '3-8-2', '3-2-8', '8-3-2', '8-2-3', '2-3-8', '2-8-3']
Edit: for all possible operands:
import re
def tokenize(s):
converter = {"-":lambda x, y:x-y, '+':lambda x, y:x+y}
total = 0
stack = re.findall('\d+|[\-\+]', s)
operator = None
for i in stack:
if i.isdigit():
if not operator:
total += int(i)
else:
total = converter[operator](total, int(i))
operator = None
else:
operator = i
return total
new_list = set(list(itertools.chain(*list(itertools.chain(*[[[''.join([''.join('{}'+i) for i in b]+['{}']).format(*c) for b in itertools.permutations(['-', '+'], len(c)-1)] for c in itertools.permutations(input, x)] for x in range(2, len(input)+1)])))))
final_list = {tokenize(a):a for a in new_list}
new_final_list = [b for a, b in final_list.items()]
Output:
['3-2', '8-3', '8-2', '8-3+2', '8-2+3', '8+2', '8+3', '2-8', '3-8', '3+2-8', '2-3']
5 Comments
JapexDoe
Awesome answer, what if I had multiple operands?
Ajax1234
@JapexDoe glad to help! Regarding multiple operands, this answer will find all possible operations given a list. Do you mean an input of multiple lists, with the goal to find the operations for every one of those lists?
JapexDoe
I'm new to Python, trying to understand some of the more advanced problems. What I meant is that if I need to find both plus and minus operands with the given problem. Also: Is there a way to reduce the list down to remove all elements that yield the same outcome? (2+8 and 8+2 are both 10). Or by not using permutations? No need to spend too much time on this for me, I can probably figure something out on my own :)
Ajax1234
@JapexDoe please see my recent edit.
JapexDoe
Thanks! Your Awesome! :)
just feed your list to itertools.permutations and format accordingly in a list comprehension directly passing the tuple to format using the * operator.
import itertools
result = ["{}-{}".format(*x) for x in itertools.permutations([3, 8, 2],2)]
print(result)
result:
['3-8', '3-2', '8-3', '8-2', '2-3', '2-8']
As a side note, don't use input as a variable name as it overrides the interactive text input function.
answered Dec 7, 2017 at 14:57
Comments
Use itertools.permutations:
from itertools import permutations
input = [3, 8, 2]
output = map('-'.join, permutations(map(str, input), 2))
Comments
You can try itertools:
Data is:
input = [3, 8, 2]
import itertools
One line solution:
print(['{}-{}'.format(i[0],i[1]) for i in itertools.permutations(input,r=2)])
Detailed solution:
Above list comprehension is same as:
final_list=[]
for i in itertools.permutations(input,r=2):
final_list.append(('{}-{}'.format(i[0],i[1])))
print(final_list)
If you want the result of subtraction then:
final_list=[]
for i in itertools.permutations(input,r=2):
final_list.append((i[0]-i[1]))
print(final_list)
