Re: [Haskell-beginners] How to select items from one list depending on another

On Wed, Nov 10, 2010 at 16:08, Alexey Levan wrote:

2010/11/10 C K Kashyap :

...

Hi, I have this problem at hand -

Given two lists

list1 = [0,1,2,0,1,4]

list2 = [1,2,3,4,5,6]

I need to take items from the second list only when the corresponding item in list1 is non-zero.

list3 = map snd $ filter takeValid $ zip list1 list2 where                       takeValid (a,b) = a /= 0

Is there a shorter way?

You can use list comprehenison and pattern matching here:

list3 = [xs | (0, xs) <- zip list1 list2]

Or, since the OP asked for the "opposite": [b | (a, b) <- zip list1 list2, a /=0 ] /M -- Magnus Therning                        (OpenPGP: 0xAB4DFBA4) magnus＠therning．org          Jabber: magnus＠therning．org http://therning.org/magnus         identi.ca|twitter: magthe