Hi,
This looks like a toughy, both conceptually and implementation wise.
First, how should the Draw command decide what the user means by:
t->Draw("hit.t","hit.id == hit_list.id");
or by
t->Draw("hit.t","hit.size == hit_ref.size");
In which case should it do a lookup to find two different index that match (as David
is looking for) or do a simple index match (as it is now)?
I suppose, a new syntax could be invented to express these two differents semantics,
but it is really worth the extra complexity in syntax?
In addition, codewise it would be a non-trivial change to add this concept.
Philippe.
> -----Original Message-----
> From: owner-roottalk@pcroot.cern.ch
> [mailto:owner-roottalk@pcroot.cern.ch]On Behalf Of David Bailey (Antares
> Post Graduate)
> Sent: Thursday, July 06, 2000 10:25 AM
> To: Roottalk (E-mail)
> Subject: [ROOT] TTree::Draw and arrays
>
>
> Hi,
>
> I've been trying to use the TTree::Draw method to loop over different
> TClonesArrays and compare the values of data members of the
> objects in each
> array. Reading the release notes for v2.25, as I understand it,
> it will only
> loop over the number of entries in each array corresponding to the smaller
> of the two array sizes and will only compare entries with the same index.
> What I would like to be able to do is a double loop over all
> entries in both
> arrays and compare the values for each possible pair of entries:
>
> e.g.
>
> t->Draw("hit.t","hit.id == hit_list.id");
>
> where: hit is a TClonesArray of "hits" ( with members "t" and "id" )
> hit_list is a TClonesArray of some "hit_id" object which
> has a member
> "id" giving the corresponding value of hit.id.
>
> i.e. What I want is to be able to draw some property of "hit" iff its "id"
> corresponds to one in the "hit_list". Clearly, I could write a macro with
> the loops explicitly to do this but it would be nice to be able to do it
> automatically... Is this possible with the current release or can it be
> easily added?
>
> Thanks for your help,
>
> Cheers, Dave
>
> /------------------------------------------/
> David Bailey : Antares post-Graduate /
> Nuclear and Astrophysics Laboratory /
> Keble Road, Oxford OX1 3RH /-------/
> (01865) 273395 /------------/
> -----------------/ d.bailey2@physics.ox.ac.uk
>
>
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