Re: best way to get the list of unique keys from 2 alists

[Kevin Rodgers]

Kevin Rodgers wrote:
> I've got 2 alists of (SYMBOL . "STRING") pairs, and I need to get the
> list of unique symbol names to pass to completing-read as its TABLE
> argument: (("SYMBOL-NAME") ...)
>
> I know about remove-duplicates and union, but I'd like to avoid using
> cl*.el functions.
>
> Since completing-read seems to ignore nil entries in TABLE, this is what
> I've got now:
>
> (nconc (mapcar (lambda (assoc)
>                  (list (symbol-name (car assoc))))
>                alist-1)
>        (mapcar (lambda (assoc)
>                  (or (assq (car assoc) alist-1)
>                      (list (symbol-name (car assoc)))))
>                alist-2))
>
> Is there a cleaner way?

Since completing-read also accepts an obarray for its TABLE, I think
this might be a little better:

(let ((table (make-vector 83 0))) ; 83 is a suitable prime
  (mapc (lambda (assoc)
          (intern (symbol-name (car assoc)) table))
        alist-1)
  (mapc (lambda (assoc)
          (intern (symbol-name (car assoc)) table))
        alist-2)
  table)

--
Kevin Rodgers