I've got a python list
alist = [ [0, 4, 5, 5], [2, 2, 4, 5], [6, 7, 8,13]], [ [3, 4, 5, 5], [2, 2, 4, 5], [6, 7, 8,999] ]
I need the result is
alist = [[0,4,8,13], [3, 4, 8, 999]]
It means first two and last two numbers in each alist element.
I need a fast way to do this as the list could be huge.
The object is actually a tuple, rather than a list. This can trip you up if you're expecting it to be mutable and it's hard to read. Consider using the continuation character \ for long lines:
alist = [ [0, 4, 5, 5], [2, 2, 4, 5], [6, 7, 8,13]], [ [3, 4, 5, 5], [2, 2, 4, 5], [6, 7, 8, 999] ]
is clearer as
alist = [ [0, 4, 5, 5], [2, 2, 4, 5], [6, 7, 8,13]], \
[ [3, 4, 5, 5], [2, 2, 4, 5], [6, 7, 8, 999] ]
which also helps you spot the double bracket that makes this a tuple. For a list:
alist = [ [0, 4, 5, 5], [2, 2, 4, 5], [6, 7, 8,13], \
[ [3, 4, 5, 5], [2, 2, 4, 5], [6, 7, 8, 999] ]]
If list comprehension as suggested in Javier's answer doesn't meet your speed requirement, consider a numpy array.