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

Question

I have a list of subscriptions, for example:

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

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

[501, 501, 501, 501]

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

Answer 1

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

Answer 2

You can use 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 3

Less puffonic, functional version using map:

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

Less pythonic since it doesn't use lists. See here .