Re: Hash tables - how to look up values?

[Bastien <bzg@gnu.org>]

Hi Thorsten,

Thorsten Jolitz <tjolitz@googlemail.com> writes:

> I would need a function that does the opposite of 
>
> ,--------------------
> | (gethash key table)
> `--------------------
>
> i.e. something like 
>
> ,-------------------
> | (getkey val table)
> `-------------------
>
> that returns the corresponding key of a known (string) value in a hash
> table (similar to 'rassoc' for alists). 
>
> I could not find such a function - does it exist already?

I don't think so.  But here is a start:

(let (key-found)
  (maphash (lambda (key val)
	     (when (equal val "my_value")
	       (setq key-found key)))
	   hashtest)
  key-found)

Of course, the shortcoming is that it stops at the first key it finds,
and discards multiple keys if several have the same value.

HTH,

-- 
 Bastien