Efficiently performing arithmetic with TNtuple branches

[KAM]

Is there an efficient way to perform arithmetic with the branches of a TNtuple? By this, I mean adding and subtracting branches, multiplying a branch by a scalar, etc.

In my case, I’d like to multiply all entries in one branch by a number (e.g. multiply all elements by, say, 12), and then add this branch to another branch, element-wise (which branch the result is stored in doesn’t matter, afterwards I no longer need the original two branches). The branches in question have hundreds of millions of entries, so doing this entry-by-entry is painfully slow. Is there a better way?

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[dastudillo]

See for instance here:

TTree Draw() and dump to TGraph

Hello root people, I wish to use the TTree->Draw() fucntion to produce a TGraph. I what to use this function along with the “gOff” option. How do I do it? tree->Draw("y:x>>mygraph","z>0","gOff"); TGraph *mygraph = (TGraph*)gDirectory->Get("mygraph"); Is giving me funny behaviour later on when I wish to plot the graph, with axis not appearing, but a stats box appearing. Right now the following code is doing what I want…but I do not like the need to have a pad appear just to be a temporary hold…

where you would use TTree::Draw (e.g. tree->Draw("2*x+3*y"), save to a TGraph and then fill the new branch from the graph points (or perhaps directly fill the new branch from the GetV array/s, without going through TGraph). The arithmetics part is fast, but doesn’t directly save to a new or existing branch.
The link Rene Brun gave doesn’t seem to work anymore but it’s here (scroll down to the section he mentions):
https://root.cern/doc/master/classTTree.html#a73450649dc6e54b5b94516c468523e45