Re: multiple histos with the same name

From: Rene Brun <>
Date: Wed, 8 Jun 2005 23:30:03 +0200 (MEST)

Hi Brett,

Thanks for sending a link to your code and presentation. I had a very quick look at your system and I have the following few immediate comments:

  -your interface to booking/filling is only a very small subset    of the histogramming system. For example

    -you do not have support for variable bin width histograms
    -you do not support profile 1 and 2-D
    -you do not support 3-d histograms
    -you cannot fill with arrays
    -you cannot fill with strings

    .. just to mention a few

  -Your Fill1d(const char* pathname function and Fill2d will be    extremely inefficient.

  -In a real application, you will probably see a mixture of calls    to HistMan and normal ROOT calls. This will be very confusing.

  -people opening a normal ROOT histogram file and viewing it    via TBrowser will automatically load in memory (a la ROOT)    the histograms or other objects associated with the file.

Sorry to list only these negative points. I understand the possible benefits of an histogram manager.

Rene Brun

On Wed,
2005, Brett Viren wrote:

> Hi Rene,
> We had a similar issue with histogram name clashes. In our case it
> was triggered by multiple instances of the same analysis modules (each
> configured differently) wanting to write the same named histograms in
> one job.
> We overcame this by developing a little class (HistMan) that helps
> organize histograms in a hierarchy of TFolders which can optionally be
> rooted in the "//root/ROOT Memory" folder, thus visible from a
> TBrowser. SetDirectory(0) is called as in your example to detach the
> histogram from ROOT's bookkeeping. Each analysis module is then
> assigned a unique path in the hierarchy thus allowing same-named
> histograms to exist and be kept separate.
> This class also provides a simple Book/Fill and I/O interface. It's
> only dependent on ROOT and the code is here if anyone is interested:
> This talk gives some description:
> (You get to see the talk a week before my collaborators <grin>).
> Regards,
> -Brett.
Received on Wed Jun 08 2005 - 23:30:13 MEST

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