[Caml-list] Possible function to add to Hashtbl?

[Caml-list] Possible function to add to Hashtbl?

[Jeremy Fincher]

On the rare occasions I do find myself using the using multiple bindings of 
a
single key in a hashtbl, I also find myself needing a "remove_all" function,
which removes all the bindings to a particular key in a hashtbl.  Perhaps 
such a
function should be added to the module?

I'm sure there's a more efficient way to implement such a function in the
hashtbl module, but here's what I've been using thus far:

-----
let hashtbl_remove_all h key =
  for i=1 to List.length (Hashtbl.find_all h key) do
    Hashtbl.remove h key;
  done
-----

Jeremy


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Re: [Caml-list] Possible function to add to Hashtbl?

[Jean-Christophe Filliatre]

 > I'm sure there's a more efficient way to implement such a function in the
 > hashtbl module, but here's what I've been using thus far:
 > 
 > -----
 > let hashtbl_remove_all h key =
 >   for i=1 to List.length (Hashtbl.find_all h key) do
 >     Hashtbl.remove h key;
 >   done
 > -----

To avoid allocating the list, you can do like this:

======================================================================
let rec remove_all h k = 
  try
    let _ = Hashtbl.find h k in Hashtbl.remove h k; remove_all h k
  with Not_found -> 
    ()
======================================================================

But conversely, you compute the hash key several times.

-- 
Jean-Christophe Filliatre (http://www.lri.fr/~filliatr)

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