[DF] Display gets confused by friend columns, prints them twice #8450
Description
The following code:
#include <ROOT/RDataFrame.hxx>
#include <TFile.h>
#include <TTree.h>
int main() {
ROOT::RDataFrame(32).Define("idx", "rdfentry_").Snapshot("t1", "f.root");
ROOT::RDF::RSnapshotOptions opts;
opts.fMode = "update";
ROOT::RDataFrame("t1", "f.root")
.Define("x", "idx*idx")
.Snapshot("t2", "f.root", {"x", "idx"}, opts);
TFile f("f.root");
auto *tmain = f.Get<TTree>("t1");
auto *tfriend = f.Get<TTree>("t2");
tmain->AddFriend(tfriend);
ROOT::RDataFrame(*tmain).Display(".*", 100)->Print();
return 0;
}prints
idx | t2.x | x | t2.idx |
0 | 0 | 0 | 0 |
1 | 1 | 1 | 1 |
2 | 4 | 4 | 2 |
3 | 9 | 9 | 3 |
4 | 16 | 16 | 4 |
5 | 25 | 25 | 5 |
where idx and t2.idx are actually two different columns (one in the main tree and the other in the friend tree) but x and t2.x are two valid spellings of the same column, which should then be printed only once.
I think Display gets tripped up by the output of RLoopManager::GetColumnNames(), which reports the two valid spellings of x. It should instead use the same logic as Snapshot, which removes duplicates.