Use the Stats action to extract the statistics of a column. 
Extract the statistics relative to RDataFrame columns and store them in TStatistic instances.
 
import ROOT
 
      .Define("w", "return 1./(v+1)")
 
 
ROOT::Detail::TRangeCast< T, true > TRangeDynCast
TRangeDynCast is an adapter class that allows the typed iteration through a TCollection.
 
ROOT's RDataFrame offers a modern, high-level interface for analysis of data stored in TTree ,...
 
   OBJ: TStatistic      Mean = 127.5 +- 4.628   RMS = 74.045   Count = 256    Min = 0     Max = 255
 OBJ: TStatistic      Mean = 40.8 +- 12.86    RMS = 60.318   Count = 256    Min = 0     Max = 255
- Date
 - April 2019 
 
- Author
 - Danilo Piparo (CERN) 
 
Definition in file df031_Stats.py.