How to split a list into a given number of sub-lists in python [duplicate]

Question

Possible Duplicates:
splitting a list of arbitrary size into only roughly N-equal parts
How do you split a list into evenly sized chunks in Python?

I need to create a function that will split a list into a list of list, each containing an equal number of items (or as equal as possible).

e.g.

def split_lists(mainlist, splitcount):
    ....


mylist = [1,2,3,4,5,6]

split_list(mylist,2) will return a list of two lists of three elements - [[1,2,3][4,5,6]].

split_list(mylist,3) will return a list of three lists of two elements.

split_list(mylist,4) will return a list of two lists of two elements and two lists of one element.

I don't care which elements appear in which list, just that the list is divided up as evenly as possible.

Answer 1

numpy.split does this already:

• http://docs.scipy.org/doc/numpy/reference/generated/numpy.split.html

Examples:

>>> mylist = np.array([1,2,3,4,5,6])

split_list(mylist,2) will return a list of two lists of three elements - [[1,2,3][4,5,6]].

>>> np.split(mylist, 2)
[array([1, 2, 3]), array([4, 5, 6])]

split_list(mylist,3) will return a list of three lists of two elements.

>>> np.split(mylist, 3)
[array([1, 2]), array([3, 4]), array([5, 6])]

split_list(mylist,4) will return a list of two lists of two elements and two lists of one element.

You may probably want to add an exception capture for the cases when the remainder of length(mylist)/n is not 0:

>>> np.split(mylist, 4)
ValueErrorTraceback (most recent call last)
----> 1 np.split(mylist, 4)
...
ValueError: array split does not result in an equal division