This function takes a list and pulls it apart into a user-defined number of pieces. It acts like a sort of reverse zip function (although it deals with only the very simplest cases).
Python, 20 lines
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Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | def unzip(p, n):
"""Split a list-like object, 'p', into 'n' sub-lists by taking
the next unused element of the main list and adding it to the
next sub-list. A list of tuples (the sub-lists) is returned.
Each of the sub-lists is of the same length; if p%n != 0, the
shorter sub-lists are padded with 'None'.
Example:
>>> unzip(['a','b','c','d','e'], 3)
[('a', 'd'), ('b', 'e'), ('c', None)]
"""
(mlen, lft) = divmod(len(p),n) # find length of longest sub-list
if lft != 0: mlen += 1
lst = [[None]*mlen for i in range(n)] # initialize list of lists
for i in range(len(p)):
(j, k) = divmod(i, n)
lst[k][j] = p[i]
return map(tuple, lst)
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This recipe was useful to me recently when I had to take a Python list and break it down into a number of different pieces, putting each consecutive item of the list into a separate sub-list.
The best way to "unzip" a list is using the zip function in this way:
you can read more details in the zip documentation.