Is there an easier way to break a list into sub groups

Shalabh Chaturvedi shalabh at cafepy.com
Sun Feb 22 00:02:20 EST 2004


MetalOne wrote:

> The following does what I want, but I feel like this could maybe be a
> one liner.
> I just can't think of anything shorter.
> If there is nothing shorter, does this seem like a candidate for
> inclusion in the standard library somewhere.
> 
>>>> def groups(l, n):
>       """l is an input list.
>          n is the size of the sub group
>          returns a list of the sub groups
>       """
> ...   i=0
> ...   g = []
> ...   while i < len(l):
> ...     g.append(l[i:i+n])  #append sub group to g
> ...     i+=n
> ...   return g
> ...
>>>> l = [1,2,3,4,5,6]
>>>> groups(l,2)
> [[1, 2], [3, 4], [5, 6]]
>>>> groups(l,3)
> [[1, 2, 3], [4, 5, 6]]
>>>> groups(l,4)
> [[1, 2, 3, 4], [5, 6]]

It's generally considered more Pythonic to use the range() function instead
of incrementing counters while looping. Also, list comprehensions are a
useful tool. These combined give us one possible solution:

>>> l = range(10)
>>> n = 2
>>> [l[i:i+n] for i in range(0, len(l), n)]
[[0, 1], [2, 3], [4, 5], [6, 7], [8, 9]]
>>> n = 3
>>> [l[i:i+n] for i in range(0, len(l), n)]
[[0, 1, 2], [3, 4, 5], [6, 7, 8], [9]]
>>>


HTH,
Shalabh



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