list comprehension to merge various lists in pytho

问题:

I need to plot a lot of data samples, each stored in a list of integers. I want to create a list from a lot of concatenated lists, in order to plot it with enumerate(big_list) in order to get a fixed-offset x coordinate. My current code is:

biglist = []
for n in xrange(number_of_lists):
    biglist.extend(recordings[n][chosen_channel])
for x,y in enumerate(biglist):
    print x,y

Notes: number_of_lists and chosen_channel are integer parameters defined elsewhere, and print x,y is for example (actually there are other statements to plot the points.

My question is: is there a better way, for example, list comprehensions or other operation, to achieve the same result (merged list) without the loop and the pre-declared empty list?

Thanks

回答1:

import itertools
for x,y in enumerate(itertools.chain(*(recordings[n][chosen_channel] for n in xrange(number_of_lists))):
    print x,y

You can think of itertools.chain() as managing an iterator over the individual lists. It remembers which list and where in the list you are. This saves you all memory you would need to create the big list.

回答2:

>>> import itertools
>>> l1 = [2,3,4,5]
>>> l2=[9,8,7]
>>> itertools.chain(l1,l2)
<itertools.chain object at 0x100429f90>
>>> list(itertools.chain(l1,l2))
[2, 3, 4, 5, 9, 8, 7]