Re: [Haskell-beginners] Padding List with Zeros

Hey Lorenzo-- Here's at least a partial solution to the specific case you describe: a=[0,10,20,30,40,50] b=[0,10,50] c=[2,1,-5] d [] _ _ = [] d a [] c = d a [0] c d a b [] = d a b [0] d a b c | head a == head b = (head c) : d (tail a) (tail b) (tail c) | otherwise = 0 : d (tail a) b c main = do print $ d a b c I don't know if it will do what you want if the lists aren't perfectly sized as they are in your example (meaning your example has all the lists expire at exactly the same iteration). In this example it will pad out to zero to the size of a. Someone may come up with a better example, I'm still learning as I go too. I was just looking for an opportunity to give back to the list. Cheers-- Greg On Sep 15, 2010, at 12:28 AM, Lorenzo Isella wrote:

Hi Antoine, Unfortunately these are really truly lists and not sets (for instance, the ordering of elements matter and some of them may be repeated).

Lorenzo

On 09/15/2010 01:55 AM, Antoine Latter wrote:

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Are these truly lists, or would you be better suited using Sets, Maps or IntMaps?

Then you can use some of the unionWith functions to decide what to insert, or you can simply wrap the looking functions to return zero on failure.

...

Antoine

On Sep 14, 2010 6:35 PM, "Lorenzo Isella" mailto:lorenzo.isella@gmail.com> wrote:

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Dear All, I still have to find my way with immutable lists and list comprehension. Consider the following lists

A=[0,10,20,30,40,50] B=[0,10,50] (i.e. B is a subset of list A; list A is already ordered in increasing order and so is B). C=[2,1,-5] i.e. there is a corresponding element in C for every element in B.

Now, I would like to define a new list D having length equal to the length of A. The elements of D in the position of the elements of A in common with B are equal to the corresponding entries in C, whereas the other ones are zero i.e. D=[2,1,0,0,0,-5]. How can I achieve that? The first thought that comes to my mind is to define a list of zeros which I would modify according to my needs, but that is not allowed... Many thanks

Lorenzo _______________________________________________ Beginners mailing list Beginners@haskell.org mailto:Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

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