List comprehensions in python

Question

Is there any way I can combine two list a and b into c using list comprehensions in python,

a=[1,2,3]
b=['a','b']

c=['1a','1b','2a','2b','3a','3b']

possible duplicate of [Get the cartesian product of a series of lists in Python](http://stackoverflow.com/questions/533905/get-the-cartesian-product-of-a-series-of-lists-in-python) (also see http://stackoverflow.com/questions/4481724/python-convert-list-of-char-into-string). — Felix Kling, Apr 23 '12 at 14:54

jamylak · Answer 1 · 2012-04-23T15:07:34.277

6

>>> from itertools import product
>>> a=[1,2,3]
>>> b=['a','b']
>>> ['%d%s' % el for el in product(a,b)]
['1a', '1b', '2a', '2b', '3a', '3b']

With new string formatting

>>> ['{0}{1}'.format(*el) for el in product(a,b)]
['1a', '1b', '2a', '2b', '3a', '3b']

edited Apr 23 '12 at 15:07

answered Apr 23 '12 at 14:54

jamylak

+1 This is a better solution as product will be far more efficient than nested loops, and more flexible. – Gareth Latty Apr 23 '12 at 16:24

score 6 · Accepted Answer · answered Apr 23 '12 at 14:56

6

>>> a = [1,2,3]
>>> b = ['a', 'b']
>>> c = ['%d%c' % (x, y) for x in a for y in b]
>>> c
['1a', '1b', '2a', '2b', '3a', '3b']

answered Apr 23 '12 at 14:56

Maehler

score 2 · Answer 3 · answered Apr 23 '12 at 14:55

2

use c = ["%d%s" % (x,y) for x in a for y in b]

answered Apr 23 '12 at 14:55

gefei

score 2 · Answer 4 · answered Apr 23 '12 at 14:56

2

List comprehensions can loop over multiple objects.

In[3]: [str(a1)+b1 for a1 in a for b1 in b]

Out[3]: ['1a', '1b', '2a', '2b', '3a', '3b']

Note the slight subtlety of converting the number into a string.

answered Apr 23 '12 at 14:56

Andrew Jaffe

score 2 · Answer 5 · answered Apr 23 '12 at 14:56

2

Just use the "nested" version.

c = [str(i) + j for i in a for j in b]

answered Apr 23 '12 at 14:56

Xion

score 2 · Answer 6 · answered Apr 23 '12 at 15:05

2

import itertools
c=[str(r)+s for r,s in itertools.product(a,b)]

answered Apr 23 '12 at 15:05

mkurmag

score 1 · Answer 7 · answered Apr 23 '12 at 15:08

1

somewhat similar version of jamylak's solution:

>>> import itertools
>>> a=[1,2,3]
>>> b=['a','b']
>>>[str(x[0])+x[1] for x in itertools.product(a,b)]
['1a', '1b', '2a', '2b', '3a', '3b']

answered Apr 23 '12 at 15:08

Ashwini Chaudhary

7 Answers7