I am concerned that TTree::Draw performance is significantly faster than a manual iteration over the tree (see below). Is there a way to make it on-par with TTree::Draw? #include <iostream> #include <TFile.h> #include <TTree.h> using namespace std; int main(int argc, char *argv[]) { TFile *…

Hi, for reading just a single branch which is a double it should not be the case. I see that you are reading a file on afs: is the measurement fair (e.g. no glitches, warm caches and so on)? D

Beware also that TTree::Draw implicitly converts all data to doubles. In your case it does not matter because you have doubles, but If you had large integer values (ULong64_t) in your branch, this can lead to rounding errors. So the loop is more exact than TTree::Draw (and thus not completely equiva…

I ran these two simple scripts on both - lxplus and my laptop hard drive. The results are very similar. The execution time is 3 seconds with TTree::Draw vs 2-4 minutes with the loop. This suggests that TTree::Draw is faster than the loop by x100! Thank you for your help! get_weights.cxx (822 Bytes…

(hit twice by mistake; need to delete this post)

Hi, for completeness, could you provide the input file too? D

Try the attached code (I assume that you use it as a “compiled executable”, not as an “interpreted macro”). get_weights.cxx (779 Bytes)

I can confirm, the code example from Pepe Le Pew works just as fast as compiled TTree::Draw - both take 2 seconds to run. Do we know why in my original code it’s not that fast? I would think that disabling all branches except the one we are interested in is essentially the same as in Pepe’s example…

Thanks Pepe for the link! It explains difference between the two approaches. Meanwhile I also discovered that your way of getting a pointer to the branch, i.e. TBranch *b_mcWeightOrg; tree->SetBranchAddress("mcWeightOrg", &mcWeightOrg, &b_mcWeightOrg); leads to about 3 times faster iterati…

leads to about 3 times faster iteration in the loop, than this one Where do you place the code in this case? [Note that the SetBranchAddress branch is superior as its supports TChain while the GetBranch/SetAddress does not or need to be called wastefully within the loop). Cheers, Philippe.

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TTree::Draw vs loop

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Pepe_Le_Pew April 15, 2016, 1:02pm 9

Leak when reading std::vector ROOT

I think if one wanted to read individual branches, the code would contain something like: Both the technique I shown and the technique using BranchStatus will work. Using BranchStatus is slightly slower (especially for TTree with large number of branches) as each GetEntry needs to always ask which branches are enabled (and the selection using a sorta regex is a bit more cumbersome). So the answer to [quote]“Do I really need the TBranch?”.[/quote]Yes if you want to read only that branch (a…

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