TChain::Draw histogram filling limit

ROOT
1

I have chained many TTrees together into a TChain. The chain now has about 4.3e9 entries. When I use the TChain::Draw like this:

TH1D *hnorm = new TH1D(“shift_norm”,“shift_norm”,nbins,xstart,xend);

ch->Draw(“shift>>shift_norm”,"","");

I do not appear to be getting the full number of entries in the histogram, rather just 1e9 entries exactly. Is there a limit that I’m not aware of somewhere? I know about the ch->SetEstimate() but I thought that only applied to extracting the values from the chain in vector form.

2

Try:

ch->Draw("shift>>shift_norm", "", "", 10000000000LL); // 1e10

or:

ch->Draw("shift>>shift_norm", "", "", ch->GetEntries());
3

Which version of ROOT are you using?

4

I meant to write that down, but perhaps I forgot due to embarrassment: ROOT v5.34/05, I have C++11 issues on my system so upgrading to ROOT 6 is something I’ve been avoiding.

5

This problem is indeed fixed in v6. To work around the problem in v5, either follow Pepe’s suggestion or call (once before any of the Draw)
ch->GetEntries();

Cheers,
Philippe.

6

Philippe, note that in ROOT 5, TChain::kBigNumber = 1.23456789e9 and so the original problem will always be present (unless a sufficiently high “nentries” is given in the “Draw” statement).

7

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