How to group list items into tuple?

Question

I have a list of numbers, how can I group every n numbers into a tuple?

For example, if I have a list a = range(10) and I want to group every 5 items into a tuple, so:

b = [(0,1,2,3,4),(5,6,7,8,9)]

How can I do this? I also want to raise an error if len(a) is not an integer multiple of n.

http://stackoverflow.com/questions/434287/what-is-the-most-pythonic-way-to-iterate-over-a-list-in-chunks — avasal, Mar 07 '13 at 08:52

score 12 · Answer 1 · answered Mar 07 '13 at 08:46

12

>>> a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> [tuple(a[i:i+5]) for i in range(0, len(a), 5)]
[(0, 1, 2, 3, 4), (5, 6, 7, 8, 9)]

answered Mar 07 '13 at 08:46

linbo

2,393
3
22
45

score 1 · Answer 2 · answered Mar 07 '13 at 08:58

In [18]: def f(lst,n):    
    ...:     if len(lst)%n != 0:
    ...:         raise ValueError("{} is not a multiple of {}".format(len(lst),n))
    ...:     return zip(*[iter(lst)]*n)

In [19]: lst = range(10)

In [20]: f(lst,5)
Out[20]: [(0, 1, 2, 3, 4), (5, 6, 7, 8, 9)]

In [21]: f(range(9),5)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-21-814a68e0035f> in <module>()
----> 1 f(range(9),5)

<ipython-input-18-3ca911a04fd3> in f(lst, n)
      1 def f(lst,n):
      2     if len(lst)%n != 0:
----> 3         raise ValueError("{} is not a multiple of {}".format(len(lst),n))
      4     return zip(*[iter(lst)]*n)

ValueError: 9 is not a multiple of 5

This looks great! Thanks! Although I'm not sure how did `zip(*[iter(lst)]*n)` work... — LWZ, Mar 07 '13 at 09:04
@LWZ -- if you read through the questions, linked in the comments, you will find different implementations of the actual splitting with corresponding discussion... — root, Mar 07 '13 at 09:07

score 1 · Answer 3 · answered Mar 07 '13 at 09:09

1

determine that N is your group length

if (len(your_list)%n==0):
    wish_list = [ tuple(your_list[i:i+N]) for i in range(0, len(your_list), N) ]
else:
    raise Exception("not divisible by N")

answered Mar 07 '13 at 09:09

How to group list items into tuple?

3 Answers3

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