I have a following list:
mylist = ['car', 'truck', 'ship']
Currently I am able to only get all the possible combinations of 2 strings using this:
from itertools import combinations
print(list(combinations(mylist,2)))
which gives me:
[('car', 'truck'), ('car', 'ship'), ('truck', 'ship')]
However, one combination is actually all the 3 strings. Thus I would like my outcome to be:
[('car', 'truck'), ('car', 'ship'), ('truck', 'ship'), ('car', 'truck', 'ship')]
This is an adjusted case of the powerset. Typically the code for the powerset in Python looks like this:
from itertools import chain, combinations
def powerset(it):
yield from chain.from_iterable(combinations(it, r) for r in range(len(it)+1))
You can change it, though, to only accept results within a certain range. In your case, it's from 2 to the 3:
from itertools import chain, combinations
def adjusted_powerset(it):
yield from chain.from_iterable(combinations(it, r) for r in range(2, 3))
See it in action here.
If you need it to become more general, play with the range parameters. A nice template would be to create a powerset helper:
from itertools import chain, combinations
def powerset_helper(it, start, stop):
yield from chain.from_iterable(combinations(it, r) for r in range(start, stop+1))
def powerset(it):
yield from powerset_helper(it, 0, len(it))
def adjusted_powerset(it):
yield from powerset_helper(it, 2, 3)
How about this,
from itertools import combinations
mylist = ['car', 'truck', 'ship']
result = list()
for r in [2, 3]:
result.extend(combinations(mylist, r))
print(result)
[('car', 'truck'), ('car', 'ship'), ('truck', 'ship'), ('car', 'truck', 'ship')]
Actually, another combination is collections containing only one word, as well as the empty set. The set of all possible combinations n choose k for all * 0 <= k <= n* is called the powerset of the collection.
The documentation page of itertools gives an example of how to produce it. I have slightly modified it to accept a minlength variable (in your case minlength=2)
def powerset(iterable, minlength=0):
"powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)"
s = list(iterable)
return chain.from_iterable(combinations(s, r) for r in range(minlength, len(s)+1))
filter to this which removes all neither-length-2-nor-3 combinations.
itertools.combinations supports list length as an input parameter.
def combinations(iterable, r):
# combinations('ABCD', 2) --> AB AC AD BC BD CD
# combinations(range(4), 3) --> 012 013 023 123
pool = tuple(iterable)
n = len(pool)
if r > n:
return
indices = range(r)
yield tuple(pool[i] for i in indices)
while True:
for i in reversed(range(r)):
if indices[i] != i + n - r:
break
else:
return
indices[i] += 1
for j in range(i+1, r):
indices[j] = indices[j-1] + 1
yield tuple(pool[i] for i in indices)
For your case, simply add 2-string and 3-string together:
from itertools import combinations
print(list(combinations(mylist,2)) + list(combinations(mylist,3)))
('car')not in your result? what is it you actually need?list(set(combinations(mylist,2)).union(set(combinations(mylist, 3))]