Re: [ferret_users] number of opened datasets

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

David Wang wrote:
> Thank you, Ansley.
>
> It's a nice workaround, providing I don't change the current dataset 
> with SET DATA.
Yes, true. In a future version we'll add a symbol that lets the user get 
the total number of open datasets though. We've been working on adding 
more of this kind of thing, to let you access information that Ferret 
knows but doesn't make available to the programmer to use in scripts.

You could also do something of the sort yourself, by setting up a symbol 
that you increment every time you open a dataset, which might be 
feasible if you always use a script to open the dataset.  This kind of 
thing, having small "utility" scripts that do operations, are useful 
when a set of scripts will be used over and over to do similar things 
but with different inputs.

  yes? GO open_a_dset  datatsetname.nc

and then open_a_dset.jnl opens the dataset, maybe checks to see that 
this was successful, and increments the counter.  This particular script 
would let the calling script continue if one dataset was unavailable 
(something you might NOT want to do!)

  ! open_a_dset.jnl

  SET MODE ignore_error 
  USE $1
  IF ($ferret_last_error"0|*>1") EQ 1` THEN
      ECHO "error opening dataset" $1 !Ferret will have issued error 
msgs, too...
      EXIT/SCRIPT
  ENDIF
  CANCEL MODE ignore_error

  DEFINE SYMBOL n_open_dsets = ($n_open_dsets"0") + 1  
  EXIT


Ansley
> David
>
> Ansley Manke wrote:
> > Hi David,
> > There isn't such a symbol, per se. (That's a good  idea though).  
> > However you can get this information if you know a variable in the 
> > last dataset opened, by using `var,RETURN=dsetnum`
> >
> >     yes? use etopo120
> >     yes? use etopo60
> >     yes? use etopo20
> >
> >     yes? let dsetnum = `rose,return=dsetnum`
> >      !-> DEFINE VARIABLE dsetnum = 3
> >
> >
> >
> > David Wang wrote:
> > > Hi Ferreters,
> > >
> > > I wonder if there is any system symbol (or means) keeping track of 
> > > the number of opened datasets in the current session. I'd like loop 
> > > around all datasets with the command:
> > >
> > > repeat/name=m/range=1:`number_of_datasets` let/data=`m` v2 = v1[t=@ave]
> > >
> > > without manually counting and specifying the number of datasets.
> > >
> > > Thanks,
> > > David