Show usage of RDataFrame's helper tools, contained in ROOT/RDFHelpers.hxx.
Author: Enrico Guiraud (CERN)
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Monday, March 27, 2023 at 09:46 AM.
First of all, we create a dataframe with 3 entries and define two simple columns
const auto nEntries = 3;
ROOT::RDataFrame _df(nEntries);
auto df = _df.Define("one", [] { return 1; }).Define("two", [] { return 2; });
*** Not ***
This helper takes a callable f (which must return a bool) and produces a new callable which takes the same
arguments as f but returns its negated result. Not is useful to invert the check performed by a given Filter.
Here we define a simple lambda that checks whether a value is equal to 1, and invert it with Not:
auto isOne = [] (int a) { return a == 1; };
auto isNotOne = ROOT::RDF::Not(isOne);
Both isOne and isNotOne are callables that we can use in Filters:
auto c1 = df.Filter(isOne, {"one"}).Count();
auto c2 = df.Filter(isNotOne, {"two"}).Count();
Both counts are equal to the total number of entries, as both Filters always pass.
R__ASSERT(*c1 == nEntries);
R__ASSERT(*c2 == nEntries);
*** PassAsVec *** Consider the following function, which checks if a vector consists of two elements equal to 1 and 2:
auto checkOneTwo = [] (const std::vector<int> &v) { return v.size() == 2 && v[0] == 1 && v[1] == 2; };
The following line, although it looks reasonable, would not run correctly:
df.Filter(checkOneTwo, {"one", "two"});
The reason is that Filter(..., {"one", "two"}) expects a callable that takes exactly two integers, while
checkOneTwo actually takes a vector of integers (i.e. it does not have the right signature).
PassAsVec helps passing down the single values "one", "two" to checkOneTwo as a collection: it takes a callable
f that expects a collection as argument and returns a new callable that takes single arguments instead, passes
them down to f and returns what f returns.
PassAsVec requires that number of arguments and their type is specified as template argument.
Here's an example usage (remember, PassAsVec(f) returns a new callable!):
auto c3 = df.Filter(ROOT::RDF::PassAsVec<2, int>(checkOneTwo), {"one", "two"}).Count();
R__ASSERT(*c3 == nEntries);
Draw all canvases
gROOT->GetListOfCanvases()->Draw()