I have a list:
[0, 1, 2, 3, 4, 5]
I would like to combine the first item all others except the last. The result should be a list, as the list below:
[[0], [0,1], [0,2], [0,3], [0,4], [0,1,2], [0,1,3] [0,1, 4], [0,2,3], [0,2,4], [0,3,4], [0,1,2,3], [0,1,2,4], [0, 2,3,4], [0,1,2,3,4]]
How can I do this? Thank you!
import itertools
a = [0, 1, 2, 3, 4, 5]
base = (a[0],)
items = a[1:-1]
combos = [base + combo for length in range(len(items)+1) for combo in itertools.combinations(items, length)]
# In case it matters that the sublists are lists rather than tuples:
combos = [list(combo) for combo in combos]
print combos
# [[0], [0, 1], [0, 2], [0, 3], [0, 4], [0, 1, 2], [0, 1, 3], [0, 1, 4], [0, 2, 3], [0, 2, 4], [0, 3, 4], [0, 1, 2, 3], [0, 1, 2, 4], [0, 1, 3, 4], [0, 2, 3, 4], [0, 1, 2, 3, 4]]
combos = [[base + combo ... and removing the next line. (also you can write range(len(items)+1) instead of range(0, len(items)+1))
chain.from_iterable step, too.First compute the power set of the all but the first item. Searching on "python power set" you'll get several hits, including this one. You didn't specifically mention it, but you probably want the results in lexographical order, and the implementation I selected gets you most of the way there.
That will give you all the combinations you need, .e.g [[], 1, ..., [1,2,3,4,5]] (note this includes the empty set and the whole set itself). Now just prepend 0 to each of these gives [[0],[0,1],...[0,1,2,3,4,5]].
This problem is related to powersets
>>> L = [0, 1, 2, 3, 4, 5]
>>> [[L[0]] + [k for j,k in enumerate(L[1:-1]) if i>>j&1] for i in range(1<<(len(L)-2))]
[[0], [0, 1], [0, 2], [0, 1, 2], [0, 3], [0, 1, 3], [0, 2, 3], [0, 1, 2, 3], [0, 4], [0, 1, 4], [0, 2, 4], [0, 1, 2, 4], [0, 3, 4], [0, 1, 3, 4], [0, 2, 3, 4], [0, 1, 2, 3, 4]]
If you want them sorted shortest to longest:
>>> M = [[L[0]] + [k for j,k in enumerate(L[1:-1]) if i>>j&1] for i in range(1<<(len(L)-2))
>>> sorted(M, key=len)
[[0], [0, 1], [0, 2], [0, 3], [0, 4], [0, 1, 2], [0, 1, 3], [0, 2, 3], [0, 1, 4], [0, 2, 4], [0, 3, 4], [0, 1, 2, 3], [0, 1, 2, 4], [0, 1, 3, 4], [0, 2, 3, 4], [0, 1, 2, 3, 4]]
Its a combination of the first element plus the powerset of all the elements minus the first and last elements:
from itertools import chain, combinations
test = [0, 1, 2, 3, 4, 5]
def powerset(iterable):
"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(len(s)+1))
print [test[:1] + list(c) for c in powerset(test[1:-1])]
# [[0], [0, 1], [0, 2], [0, 3], [0, 4], [0, 1, 2], [0, 1, 3], [0, 1, 4], [0, 2, 3], [0, 2, 4], [0, 3, 4], [0, 1, 2, 3], [0, 1, 2, 4], [0, 1, 3, 4], [0, 2, 3, 4], [0, 1, 2, 3, 4]]
Here is a generator.
from itertools import combinations
def custom_combination_gen(l):
start = [l[0]]
L = l[1:-1]
yield start
for y in range(1, len(L)+1):
for x in combinations(L, y):
yield start + list(x)
Running the code:
print list(custom_combination_gen([0,1,2,3,4,5]))
[[0], [0, 1], [0, 2], [0, 3], [0, 4], [0, 1, 2], [0, 1, 3], [0, 1, 4], [0, 2, 3], [0, 2, 4], [0, 3, 4], [0, 1, 2, 3], [0, 1, 2, 4], [0, 1, 3, 4], [0, 2, 3, 4], [0, 1, 2, 3, 4]]
import itertools
a = [0, 1, 2, 3, 4, 5]
myList = []
myFinalList = []
for i in xrange(0,len(a)-2): myList += list(itertools.combinations(a[1:-1],i))
for item in myList: myFinalList.append(list(item)+[a[0]])
print myFinalList
[1]excluded?