Substracting two variables in root

[souvik]

Please provide the following information:

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ROOT Version (e.g. 6.12/02):
Platform, compiler (e.g. CentOS 7.3, gcc6.2):

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I have two variables in my tree. Now I want to substract them. Can you please provide a macro for me ?

Thanks in Advance

[Wile_E_Coyote]

It depends on what you want to do with them.
The simplest thing to try would be: tree->Draw("var1 - var2");

[souvik]

Thank you very much.

[souvik]

I can substract them with that command. Can you please tell me how do I save “var1 - var2” inside another tree ?

Thanks in Advance

[Axel]

You can use RDataFrame for that:

ROOT::RDataFrame df("input.root");
df.Define("diff", "var1 - var2").Snapshot("diffTree", "output.root", {{"diff"}});

or if you want to keep the original ones, use:

...Snapshot("diffTree", "output.root", {{"var1", "var2", "diff"}});