Comprehension list on nested list (list of lists)

Question

It is allowed the use of a comprehension list on a "list of lists"? I would like to extract a list from a nested list. I did try this:

def main():
    a = ['1','2','3']
    b = ['4','5','6']
    c = ['7','8','9']
    board = [a,b,c]
    y = [x for x in board[1][i] if i in range(0,3)]
    print y

but I get "NameError: name 'i' is not defined". I'm using the wrong syntax or nested list cannot be used like this?

Thanks a lot!

What do you expect the output to be?

Martijn Pieters
– Martijn Pieters

2013-04-03 14:53:39 +00:00
Commented Apr 3, 2013 at 14:53 — Martijn Pieters
– Martijn Pieters, Commented Apr 3, 2013 at 14:53

Martijn Pieters · Accepted Answer · 2013-04-04 11:23:02Z

2

Nesting loops in list comprehensions work the same way as nesting regular for loops, one inside the other:

y = [x for i in range(3) for x in board[1][i]]

but in this case, just selecting board[1][:] would be easier and give you the same result; a copy of the middle row.

If you need to apply an expression to each column in that row, then just loop over board[1] directly:

y = [foobar(c) for c in board[1]]

edited Apr 4, 2013 at 11:23

answered Apr 3, 2013 at 14:54

Martijn Pieters

1.1m326 gold badges4.2k silver badges3.4k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Lornioiz Over a year ago

The comprehension list allows me to select a column too, not only a row. There is a faster way to return a column like you did with "board[1][:]" for the row? Thanks!

Collectives™ on Stack Overflow

Comprehension list on nested list (list of lists)

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related