What's the best way to create a list of tuples containing values taken from an array?

Question

I have three arrays/lists:

list1 = range(1,10)
list2 = range(1,10)
list3 = range(1,10)

I want to create an list of tuples containing an assortment of each of the values in my three lists. Essentially I want an output such as:

combo = [(1,1,1), (1,1,2), (1,1,3) ... (1,4,2), (1,4,3) ... (4,5,4), (4,5,5) ... (10,10,9), (10,10,10)]

It seems like such as simple problem, but I don't know where to start.

Are you looking for permutations/combinations of three for the numbers 1-10? — Zach Gates, Mar 10 '15 at 20:52
Take a look at the `itertools` module https://docs.python.org/2/library/itertools.html#itertools.permutations — thumbtackthief, Mar 10 '15 at 20:52
Just a heads up, `range(1,10)` will generate the numbers `1,2,3,...,7,8,9` -- 10 *will not* be included -- if you want that, you might change the end to 11. — jedwards, Mar 10 '15 at 20:58

Alex Riley · Accepted Answer · 2015-03-10T20:59:03.000

3

You can use itertools.product to generate the Cartesian product of lists:

>>> import itertools
>>> list(itertools.product(list1, list2, list3))
[(1, 1, 1),
 (1, 1, 2),
 (1, 1, 3),
 (1, 1, 4),
 (1, 1, 5),
 (1, 1, 6),
 (1, 1, 7),
 (1, 1, 8),
 (1, 1, 9),
 (1, 2, 1),
 (1, 2, 2),
 (1, 2, 3)
 ...

itertools.product(list1, list2, list3) returns a generator object - only when you iterate over it will the tuples be returned. In the example code above, list is used to read the contents of the generator into a Python list.

Note that you can also use the repeat parameter of itertools which is much neater when your lists range over the same elements:

list(itertools.product(list1, repeat=3))

edited Mar 10 '15 at 20:59

answered Mar 10 '15 at 20:53

Alex Riley

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Wouldn't `itertools.combinations_with_replacement(range(1, 10), 3)` also work? – Zach Gates Mar 10 '15 at 20:54
2

@zachgates: it's not quite the same thing, e.g. `(1, 2, 1) in list(itertools.combinations_with_replacement(range(1, 10), 3))` is `False` – Alex Riley Mar 10 '15 at 21:00
Ahah. Cartesian product was the keyword I was missing. – Peter Li Mar 10 '15 at 21:20

score 1 · Answer 2 · answered Mar 10 '15 at 20:53

1

If I got it right, you want a Cartesian product of 3 lists? Well, there is a function for that in itertools

import itertools

result = list(itertools.product(list1, list2, list3))

answered Mar 10 '15 at 20:53

Eli Korvigo

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Zizouz212 · Answer 3 · 2015-03-10T21:01:50.103

-1

You can also just create a list and append to it using nested loops. Just remember that if you also want the number 10, you need to change your range to range(1, 11) so that it stops at the number 11. It's like a < 11 (Doesn't include the number 11).

combo = []
for i in range(1, 11):
    for j in range(1, 11):
        for k in range(1, 11):
            a = (i, j, k)
            combo.append(a)

edited Mar 10 '15 at 21:01

answered Mar 10 '15 at 20:55

Zizouz212

4,908
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This comes close to working, although the itertools.product method is better. Note that your range functions leave off the number 10. – thumbtackthief Mar 10 '15 at 20:58
It's what the OP used (and I know, it's how the `range` works). How is it that it only comes *close to working*? – Zizouz212 Mar 10 '15 at 20:59
You don't have the number 10. You are correct that the OP made the same mistake, but it wouldn't give the desired output. – thumbtackthief Mar 10 '15 at 20:59
Sure. I'll go ahead and change it. – Zizouz212 Mar 10 '15 at 21:01

score -3 · Answer 4 · answered Mar 10 '15 at 20:56

-3

Use this :

combo=[]
for i in range(1,11):
  for j in range(1,11):
    for k in range(1,11):
      combo.append( (i,j,k) )

answered Mar 10 '15 at 20:56

Aakash

83
1
12

What's the best way to create a list of tuples containing values taken from an array?

4 Answers4