Re: Couple of questions/comments regarding TRefs in a array (5.18.00a)

Hi Constantin,

Constantin Loizides wrote:
> Dear all,
>
> I'd like to store an array of TRefs in a class that
> itself is stored in a TClonesArray. The TRefs can point
> to objects in different branches of the same tree.
> The following are my findings/questions for 5.18.00a.
>
> a) Using a TRefArray:
> TRefs stored in TRefArray seem not to support
> autoloading via TTree::BranchRef()?

correct. We will implement this possibility in a medium term version. For the time being you must associate a TRef object to the TRefArray to force the autoloading of another branch.
>
> Also not sure if TRefArray would be split?
This does not make sense. The TRefArray elements are streamed to the same buffer.
>
> Assuming the above two points could be
> made to work. What happens if I merge two trees created
> in different processes? From the description of the
> TRefArray I would rather guess that this is not
> supported?

You can perfectly merge two trees containing TRef and TRefArray. The corresponding TProcessID objects from all the files are copied to the result file.
>
> b) Using a TClonesArray of TRef
> Autoloading worked but the TClonesArray was not split.
> Is this a restriction when having a TClonesArray inside
> a TClonesArray?

This a violation of the good old principles of a TClonesArray, ie having variable length collections
in a variable length collection.
>
> c) Using a std::vector of TRef
> Autoloading and splitting works, so this is what I am
> using for now.

Yes, this should be OK, although far much less efficient (memory, time and file space wise)
than a TRefArray.
> My experience with ROOT and std::vector
> is limited however. In particular I'd like to know if
> I have to "trim" the std::vector to its minimal size
> before storing it? In other words assuming its capacity
> is bigger than its size, on read time would I recreate
> the std::vector as it was before with the larger
> capacity or would ROOT create the std::vector just with
> the needed size?

std::vector are automatically trimmed to the exact size and rebuilt at the correct length
when reading. This is done automatically.

Rene Brun
>
> Thanks,
> Constantin
>
Received on Mon Jul 14 2008 - 10:35:22 CEST