Using RNode in RDataFrame

[kpachal]

Hi there,

I’m trying to create a function like these ones:
https://root.cern.ch/doc/master/df025__RNode_8C_source.html

to apply filters to an RDataFrame. But annoyingly I can’t seem to find the right thing to #include to gain access to RNode. My best guesses for header names have failed and I can’t find an example with full code.

Help?

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ROOT Version: Not Provided
Platform: Not Provided
Compiler: Not Provided

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[eguiraud]

Hi @kpachal,
ROOT::RNode comes with #include <ROOT/RDataFrame.hxx>…if you have a recent enough ROOT version The tutorial you are linking to is for ROOT “master” (latest, unreleased ROOT). ROOT::RNode is not available e.g. in ROOT v6.14.

Could this be the issue?
If yes, you can download a compiled version of ROOT master from our website and use that one, or source a nightly build of ROOT from lcg, or compile a more recent ROOT yourself.

Cheers,
Enrico

[kpachal]

Hi Enrico,

Ah – that’d be it! I was using 6.14. I’ll try to get a more recent version, but I’m on a shared cluster so I’ll have to use what’s available. In case I’m stuck with 6.14, is there an equivalent way to do this there?

Cheers,
Kate

[eguiraud]

Hi,
note that there is no more recent release of ROOT (for now: v6.16 is coming soon, with all the RNode goodness). But you can get a nightly build of ROOT master branch from the LCG releases on cmvs, if it’s available on your cluster: source /cvmfs/sft-nightlies.cern.ch/lcg/views/dev3/latest/x86_64-slc6-gcc7-opt/setup.sh – they are kind of stable, ok to use most of the time.

Otherwise, depending on what you actually need to do with RNode, you can use a template function instead.
With C++14 auto return types it’s pretty straightforward:

// c++14
template <typename RDF_t>
auto AddFilter(RDF_t node, string_view filterStr)
 {
    return node.Filter(filterStr);
 }

This becomes more awkward in C++11, where we have to specify the return type somehow (trailing return types to the rescue):

// c++11
template <typename RDF_t>
auto AddFilter(RDF_t node, string_view filterStr) -> decltype(node.Filter(filterStr))
 {
    return node.Filter(filterStr);
 }

Feel free to ask if you encounter any further problems.
Cheers,
Enrico