manipulating lists to find different variables

The following is the first line from my list l:

 [0.0, 753.128, 990.43, 686.832, 366.922, -93.454, 1.0]

This is the result of:

 print l[0]

I want to take all the first element from all such *lines of my list and assign them to another list. How can I do it in python?

Answers


Using a list comprehension:

lists = [[1,2,3], [4,5,6]]
[ l[0] for l in lists ]

That would do it. Nicer is to use map: you map a list of lists to a list of their heads:

map( lambda l: l[0], lists )

If performance is important, you may want to create an iterator over the heads of your lists:

heads = itertools.imap( lambda l: l[0], enumerate(lists))

for head in heads:
   print head 

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