[Haskell-beginners] Padding List with Zeros

Antoine Latter aslatter at gmail.com
Tue Sep 14 19:55:24 EDT 2010

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

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.


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