String expressions in RDataFrame

Dear all,

I refer to the discussion in post. I’m learning how to use RDataFrame and I would like to know, please, how to use the string expressions. For instance, in ROOT: tutorials/dataframe/ File Reference, I don’t understand which is an


As I see, with

df.Define("b1", "(double) rdfentry_")\
  .Define("b2", "(int) rdfentry_ * rdfentry_").Snapshot(treeName, fileName)

a .root file is created but I don’t figure out which entries are obtained.
Thanks in advance for your time.
Best regards,


Dear @Chris90 ,

rdfentry_ is a special column, available within every RDataFrame, which represents the current entry being processed when you use it in a expression passed, for example, to Define or Filter. Learn more in the reference guide

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Ok thank you very much!


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