CODEWITHSUNDEEP
pythonlistlist-comprehension
heltonbiker
heltonbiker

Reputation: 27575

list comprehension to merge various lists in python

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

Upvotes: 3

Views: 1953

Answers (2)

John La Rooy
John La Rooy

Reputation: 304195

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.

Upvotes: 4

user2665694
user2665694

Reputation: 

>>> 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]

Upvotes: 3

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