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README.md

HipoDataFrame

The HipoDataFrame is a library with a class derived from the ROOT7 RDataSource class to provide an adaptor for RDataFrame to read HIPO files. An attempt is made to make this somewhat efficient.

Build Directions.

Requirements

To build the HipoDataFrame library, you will need hipo4 (the parent of this project) and you will need A modern version of ROOT, version 6.26 or later is recommended. This version of ROOT must be compiled with a newer compiler capable of C++17. (recommended gcc 9 or newer, llvm 12 or newer ). The version of ROOT must be compiled with the flag -DCMAKE_CXX_STANDARD=17, so that it has the RDataFrame library.

Recommended Way

It is recommended that you build the libHipoDataFrame.so (.dylib on Mac) library together with the HIPO library using Meson. See the main README for guidance. This will install the hipo4 and HipoDataFrame libraries in /path/to/install/location/lib

You can now load the library into root with:

source <location of ROOT>/bin/thisroot.sh
export LD_LIBRARY_PATH=/path/to/install/location/lib:${LD_LIBRARY_PATH}
root 
root [0] .L libHipoDataFrame.so

(For Mac, replace LD_LIBRARY_PATH with DYLD_LIBRARY_PATH and the .so with .dylib)

NOTE: On a system where the default compiler is NOT c++17 compatible, i.e. Linux at JLab, you have to specify the compiler to cmake. You can do so with the following lines:

module use /apps/modulefiles
module load gcc/9.3.0
module load cmake/3.22.1
source ~holtrop/root/bin/thisroot.sh
cmake .. -DCMAKE_INSTALL_PREFIX=${HOME} -DCMAKE_CXX_COMPILER=$(which g++) -DCMAKE_C_COMPILER=$(which gcc)

However, unfortunately, none of the installed versions of ROOT (in /apps, or by CLAS12) are currently C++17 compatible, so use the ROOT version installed in ~holtrop/root or your own.

Using the DataFrame

See the ROOT documentation for RDataFrame

Note: The names of the Hipo schema are mangled to avoid :: and . (period) in the name, since these indicate C++ namespace and class member. So instead of :: and . we use underscores (_).

The basics:

root 
root [0] .L libHipoDataFrame.so
root [1] auto df = MakeHipoDataFrame("rec_clas_016214.evio.00000.hipo")
root [2] df.GetColumnNames() // Shows what is in the file.
root [3] auto h_px = df.Histo1D("REC_Particle_px")
root [4] h_px->DrawClone();

The result would be a histogram of the REC::Particle.px, i.e the x component of the particle momentum for all particles in the events.

The ROOT RDataFrame is very versatile and is intended by the ROOT team as the future of data analysis. See more details on the ROOT website.