Python: how can I get rid of the second element of each sublist ?

Question

I have a list of sublists, such as:

[[501, 4], [501, 4], [501, 4], [501, 4]]

How can I get rid of the second element for each sublist ? (i.e. 4)

[501, 501, 501, 501]

Should I iterate the list or is there a faster way ? thanks

Answer 1

You can use a list comprehension to take the first element of each sublist:

xs = [[501, 4], [501, 4], [501, 4], [501, 4]]
[x[0] for x in xs]
# [501, 501, 501, 501]

Answer 2

a = [[501, 4], [501, 4], [501, 4], [501, 4]]
b = [c[0] for c in a]

Answer 3

A less pythonic, functional version using map:

a = [[501, 4], [501, 4], [501, 4], [501, 4]]
map(lambda x: x[0], a)

Less pythonic, since it does not use list comprehensions. See here.