I have three items in a list of lists:
test = [[a,b,c],[d,e,f],[g,h,i]]
I want it to look like this:
test = [[a,b,c,d,e,f],[g,h,i]]
what is the best way to do this in python?
Thanks for the help
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I guess there is a typo in your example.user189– user1892014-07-04 13:48:01 +00:00Commented Jul 4, 2014 at 13:48
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5 Answers
>>> test = [[1,2,3], [4,5,6], [7,8,9]]
>>> test[0].extend(test.pop(1)) # OR test[0] += test.pop(1)
>>> test
[[1, 2, 3, 4, 5, 6], [7, 8, 9]]
10 Comments
English Grad
Can you use pop for a range? say if I wanted to combine all 3 could I write: test[0].extend(test.pop(1:2))
falsetru
@EnglishGrad, No,
list.pop does not accept a range.English Grad
So what would I do if I wanted to put the 3 lists together? just use the + like stated below?
falsetru
@EnglishGrad, To get this:
[[1, 2, 3, 4, 5, 6, 7, 8, 9]] ?falsetru
@EnglishGrad, Using list comprehension:
[[x for xs in test for x in xs]]. If you want a flat list: [x for xs in test for x in xs] |
test = [test[0] + test[1], test[2]]
1 Comment
mhawke
You mean
[test[0]+..., not [list[0]+...If you want to flatten of an arbitrary slice, use a slice assignment and a list comprehension on the part you want to flatten.
This flatten from position n to end of the list:
>>> test = [[1,2,3],[4,5,6],[7,8,9],[10,11,12],[13,14,15]]
>>> n=2
>>> test[n:]=[[i for s in test[n:] for i in s]]
>>> test
[[1, 2, 3], [4, 5, 6], [7, 8, 9, 10, 11, 12, 13, 14, 15]]
This flattens up to n (but including n):
>>> test = [[1,2,3],[4,5,6],[7,8,9],[10,11,12],[13,14,15]]
>>> test[0:n]=[[i for s in test[0:n] for i in s]]
>>> test
[[1, 2, 3, 4, 5, 6], [7, 8, 9], [10, 11, 12], [13, 14, 15]]
This flattens in the middle (from and including n to include the additional groups specified):
>>> test = [[1,2,3],[4,5,6],[7,8,9],[10,11,12],[13,14,15]]
>>> test[n:n+2]=[[i for s in test[n:n+2] for i in s]]
>>> test
[[1, 2, 3], [4, 5, 6], [7, 8, 9, 10, 11, 12], [13, 14, 15]]
Flatten all the sublists:
>>> test = [[1,2,3],[4,5,6],[7,8,9],[10,11,12],[13,14,15]]
>>> n=len(test)
>>> test[0:n]=[[i for s in test[0:n] for i in s]]
>>> test
[[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]]
Note that in each case the slice on the assignment side is the same as the slice on the list comprehension side. This allows the use of the same slice object for each.
For the last case of flattening the whole list, obviously, you can just do test=[[i for s in test for i in s]] but the fact the logic is consistent allows you to wrap this in a function use a slice object.
1 Comment
pylang
This is awesome @dawg
You could combine the first two items in the list of list with the + operator and you should use '' for your strings
test = [['a','b','c'],['e','f','g'],['h','i','j']]
result = [test[0] + test[1], test[2]]
print result
output:
[['a', 'b', 'c', 'e', 'f', 'g'], ['h', 'i', 'j']]
Comments
Using the more_itertools package:
import more_itertools as mit
list(mit.chunked(mit.flatten(test), 6))
# [[1, 2, 3, 4, 5, 6], [7, 8, 9]]