Re: list of unique values from a TTree

Thanks for the replies.

On Fri, May 25, 2012 at 01:20:45PM +0000, Amnon Harel wrote:
> I wonder how much quicker your PyROOT solution will be if you first:
>
> tree.SetBranchStatus( '*', 0 ) # disables all branches
> tree.SetBranchStatus( 'scandata1', 1 ) # and enables the one we really need

This gains me a little in speed, but it's still an order of magnitude slower than Draw() (tens of seconds versus less than a second).

> AFAIK this is much harder in C++. I wrote a class that can handle most cases
> (too often a complicated enough tree/chain will break a ROOT event loop).
> If you want to try it out:
>
> http://www-d0.fnal.gov/~aharel/value_lister.h
> http://www-d0.fnal.gov/~aharel/value_lister.c

Thanks, I will see if these meet my needs.

On Fri, May 25, 2012 at 02:23:53PM +0100, Tim Head wrote:
> On Fri, May 25, 2012 at 2:08 PM, Rob Mahurin <rob_at_jlab.org> wrote:
> >
> >        2. Why is this (and the equivalent GetEntry loop called from
> >           CINT) so much slower that tree.Draw("scandata1")?
> >
>
> A workaround for this might be to use something along the following
> (unfortunately) multi line snippet:
>
> tree.Draw("scandata1>>h", "goff")
> v1 = tree.GetV1() # gets an array of value you just drew
> set(v1[n] for n in xrange(tree.GetEntries())

Yes! This does exactly what I want, and is quite fast. It must move all the looping from interpreted code into compiled code, or something.

Unfortunately, only the first 1000000 elements of v1 are filled, and no exception is thrown when v1[1000000] and beyond are read. (The subset that I'm fiddling with draws 1.5M entries; len(v1) reports 2147483647, an obvious lie.) I can apparently adjust this limit by calling tree.SetEstimate() before tree.Draw().

If any developers are reading, it'd be nice if the PyDoubleBuffer acted a little more like a python object: knew its own size, supported slicing, raised an IndexError (or suchlike) when appropriate, etc.

Thanks,
Rob

-- 
Rob Mahurin
University of Manitoba, Department of Physics
and Thomas Jefferson National Accelerator Facility
12000 Jefferson Avenue Suite 6, Newport News, VA 23606
office 757-269-6510; elsewhere 865-207-2594; rob_at_jlab.org