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[NEWBIE] is there an in-place map?
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Date: -- (:)
From: Jean-Christophe_Filliātre <Jean-Christophe.Filliatre@l...>
Subject: Re: [Caml-list] [NEWBIE] is there an in-place map?
Kuba Ober a écrit :
> I need functionality of map, but done in such a way that the output array
> is given as the argument, not as a return value. The closest I could get was
> 
> let inplace_map f a b = Array.blit (map f a) 0 b 0 (Array.length a)
> 
> Arrays a and b are of the same size.
> This seems very inelegant.

I guess you mean Array.map. Indeed, this is not optimal because
Array.map allocates a new array, whose contents is immediately copied
into b.

> One could use an adapter function and iteri, but that adds very noticeable 
> overhead, and doesn't seem too elegant either.
> 
> let inplace_map f a b = Array.iteri (fun i src -> b.(i) <- f src; ()) a

You may find this inelegant too, but it is clearly more efficient than
your previous version using map. Note that "; ()" can be omitted, since
the assignment <- already has type unit.

Equivalently, you could use a for loop instead of Array.iteri.

-- 
Jean-Christophe Filliātre
http://www.lri.fr/~filliatr/