Print out all combinations of elements in an array of arrays

Question

Say you had the following

x = [[1,2,3], [4,5,6], [7,8,9]]

What's the best way, say in python or ruby, to print out all combinations of the inner elements?

So the result would look like:

147,
148,
149,
157,
158,
159,
167,
...

This would lead to a more universal way of solving typical interview type questions like 'print all letter combinations of a phone number' or 'print the bit chart of number x.'

Anyway, thoughts?

Use [`itertools.product`](http://docs.python.org/2/library/itertools.html#itertools.product) in Python. — Ashwini Chaudhary, Mar 26 '14 at 15:24
Wow, searched and didn't see the list of lists one, guess using the word array threw it off enough. — adammenges, Mar 26 '14 at 21:18

score 4 · Answer 1 · answered Mar 26 '14 at 15:24

4

I'd do in Ruby :

x = [[1,2,3], [4,5,6], [7,8,9]]
x.first.product(*x[1..-1]).map{ |ary| ary.join.to_i }
# => [147,
#     148,
#     149,
#     157,
#     158,
#     159,
#     167,
#     168,
#     169,
#     247,
#     248,
#     249,
#     257,
#     258,
#     259,
#     267,
#     268,
#     269,
#     347,
#     348,
#     349,
#     357,
#     358,
#     359,
#     367,
#     368,
#     369]

answered Mar 26 '14 at 15:24

Arup Rakshit

116,827
30
260
317

...or `x.shift.product(*x)...` – Cary Swoveland Mar 26 '14 at 16:42
@CarySwoveland Then source array will loose data. Thus I didn't do that way. – Arup Rakshit Mar 26 '14 at 18:21

Hyperboreus · Accepted Answer · 2014-03-26T15:32:22.307

In python:

>>> x = [[1,2,3], [4,5,6], [7,8,9]]
>>> import itertools as it
>>> [x for x in it.product (*x) ]
[(1, 4, 7), (1, 4, 8), (1, 4, 9), (1, 5, 7), (1, 5, 8), (1, 5, 9), (1, 6, 7), (1, 6, 8), (1, 6, 9), (2, 4, 7), (2, 4, 8), (2, 4, 9), (2, 5, 7), (2, 5, 8), (2, 5, 9), (2, 6, 7), (2, 6, 8), (2, 6, 9), (3, 4, 7), (3, 4, 8), (3, 4, 9), (3, 5, 7), (3, 5, 8), (3, 5, 9), (3, 6, 7), (3, 6, 8), (3, 6, 9)]

Or if you want ints:

>>> [int(''.join(str(x) for x in x)) for x in it.product(*x)]
[147, 148, 149, 157, 158, 159, 167, 168, 169, 247, 248, 249, 257, 258, 259, 267, 268, 269, 347, 348, 349, 357, 358, 359, 367, 368, 369]

Or without string manipulation:

def makeNumber(t):
    sum (10 ** i * e for i, e in enumerate(t[::-1]))
x = [[1,2,3], [4,5,6], [7,8,9]]
print([makeNumber(x) for x in it.product(*x)])

end result is a number I think OP want – Arup Rakshit Mar 26 '14 at 15:27 — Arup Rakshit, Mar 26 '14 at 15:27
@ArupRakshit Added alternative. – Hyperboreus Mar 26 '14 at 15:29 — Hyperboreus, Mar 26 '14 at 15:29

score 1 · Answer 3 · answered Jun 02 '14 at 11:19

1

x = [[1,2,3], [4,5,6], [7,8,9]]
x.shift.product(*x).map(&:join)

answered Jun 02 '14 at 11:19

bluexuemei

233
3
12

1

I know this answer is correct but you need to provide more information explaining it – Jun 02 '14 at 11:42

Print out all combinations of elements in an array of arrays

3 Answers3