[RF] Deprecate RooDataSet constructors other than universal constructor

The `RooDataSet` constructors to construct a dataset from a part of an
existing dataset are deprecated and will be removed in ROOT 6.38. This
is to avoid interface duplication. One should use `RooAbsData::reduce()`
instead, or to change the weight column, the universal constructor with
the `Import()`, `Cut()`, and `WeightVar()` arguments.

The tutorials and tests were adjusted accordingly.

Also, fix a wrong comment in the `rf403` tutorials: they said that the
existing dataset is changed to interpret a different column as the
weight, but actually a new dataset was created. The comment is fixed in
this commit.

README/ReleaseNotes/v636/index.md

@@ -16,6 +16,7 @@ The following people have contributed to this new version:
 
 * The RooFit legacy interfaces that were deprecated in ROOT 6.34 and scheduled for removal in ROOT 6.36 are removed. See the RooFit section in the 6.34 release notes for a full list.
 * The `TPython::Eval()` function that was deprecated in ROOT 6.34 and scheduled for removal in ROOT 6.36 is removed.
+* The `RooDataSet` constructors to construct a dataset from a part of an existing dataset are deprecated and will be removed in ROOT 6.38. This is to avoid interface duplication. Please use `RooAbsData::reduce()` instead, or if you need to change the weight column, use the universal constructor with the `Import()`, `Cut()`, and `WeightVar()` arguments.
 
 ## Python Interface
 

core/foundation/inc/ROOT/RConfig.hxx

@@ -491,6 +491,14 @@
 # define _R__DEPRECATED_636(REASON) _R_DEPRECATED_REMOVE_NOW(REASON)
 #endif
 
+/* USE AS `R__DEPRECATED(6,38, "Not threadsafe; use TFoo::Bar().")`
+   To be removed by 6.38 */
+#if ROOT_VERSION_CODE <= ROOT_VERSION(6,37,0)
+# define _R__DEPRECATED_638(REASON) _R__DEPRECATED_LATER(REASON)
+#else
+# define _R__DEPRECATED_638(REASON) _R_DEPRECATED_REMOVE_NOW(REASON)
+#endif
+
 /* USE AS `R__DEPRECATED(7,00, "Not threadsafe; use TFoo::Bar().")`
    To be removed by 7.00 */
 #if ROOT_VERSION_CODE < ROOT_VERSION(6,99,0)

roofit/roofitcore/inc/RooDataSet.h

@@ -26,9 +26,10 @@ class TDirectory;
 #include "RooAbsData.h"
 #include "RooDirItem.h"
 
-#include <string_view>
+#include <ROOT/RConfig.hxx> // for R__DEPRECATED
 
 #include <list>
+#include <string_view>
 
 class RooDataSet : public RooAbsData, public RooDirItem {
 public:
@@ -43,9 +44,11 @@ class RooDataSet : public RooAbsData, public RooDirItem {
 
     // Constructor for subset of existing dataset
   RooDataSet(RooStringView name, RooStringView title, RooDataSet *data, const RooArgSet& vars,
-             const char *cuts=nullptr, const char* wgtVarName=nullptr);
+             const char *cuts=nullptr, const char* wgtVarName=nullptr)
+  R__DEPRECATED(6,38, "Use RooAbsData::reduce(), or if you need to change the weight column, the universal constructor with the Import(), Cut(), and WeightVar() arguments.");
   RooDataSet(RooStringView name, RooStringView title, RooDataSet *data, const RooArgSet& vars,
-             const RooFormulaVar& cutVar, const char* wgtVarName=nullptr) ;
+             const RooFormulaVar& cutVar, const char* wgtVarName=nullptr)
+  R__DEPRECATED(6,38, "Use RooAbsData::reduce(), or if you need to change the weight column, the universal constructor with the Import(), Cut(), and WeightVar() arguments.");
 
   RooDataSet(RooDataSet const & other, const char* newname=nullptr) ;
   TObject* Clone(const char* newname = "") const override {

roofit/roofitcore/test/stressRooFit_tests.h

@@ -2530,11 +2530,10 @@ class TestBasic403 : public RooUnitTest {
       RooFormulaVar wFunc("w", "event weight", "(x*x+10)", x);
 
       // Add column with variable w to previously generated dataset
-      RooRealVar *w = (RooRealVar *)data->addColumn(wFunc);
+      data->addColumn(wFunc);
 
       // Instruct dataset d in interpret w as event weight rather than as observable
-      RooDataSet dataw(data->GetName(), data->GetTitle(), data.get(), *data->get(), nullptr, w->GetName());
-      // data->setWeightVar(*w) ;
+      RooDataSet dataw{data->GetName(), data->GetTitle(), *data->get(), Import(*data), WeightVar("w")};
 
       // U n b i n n e d   M L   f i t   t o   w e i g h t e d   d a t a
       // ---------------------------------------------------------------

roofit/roofitcore/test/testSumW2Error.cxx

@@ -130,10 +130,9 @@ TEST(SumW2Error, ExtendedFit)
    auto *w = dataNoWeights->addColumn(*wFunc);
    RooDataSet data{dataNoWeights->GetName(),
                    dataNoWeights->GetTitle(),
-                   dataNoWeights.get(),
                    *dataNoWeights->get(),
-                   "",
-                   w->GetName()};
+                   RooFit::Import(*dataNoWeights),
+                   RooFit::WeightVar(w->GetName())};
    RooDataHist datahist{"datahist", "datahist", *data.get(), data};
 
    RooArgSet params;

tutorials/roofit/rf403_weightedevts.C

@@ -22,10 +22,11 @@
 #include "TAxis.h"
 #include "RooPlot.h"
 #include "RooFitResult.h"
-using namespace RooFit;
 
 void rf403_weightedevts()
 {
+   using namespace RooFit;
+
    // C r e a t e   o b s e r v a b l e   a n d   u n w e i g h t e d   d a t a s e t
    // -------------------------------------------------------------------------------
 
@@ -46,13 +47,13 @@ void rf403_weightedevts()
    RooFormulaVar wFunc("w", "event weight", "(x*x+10)", x);
 
    // Add column with variable w to previously generated dataset
-   RooRealVar *w = (RooRealVar *)data->addColumn(wFunc);
+   data->addColumn(wFunc);
 
    // Dataset d is now a dataset with two observable (x,w) with 1000 entries
    data->Print();
 
-   // Instruct dataset wdata in interpret w as event weight rather than as observable
-   RooDataSet wdata(data->GetName(), data->GetTitle(), data.get(), *data->get(), 0, w->GetName());
+   // Create a new dataset wdata where w is interpreted as event weight rather than as observable
+   RooDataSet wdata(data->GetName(), data->GetTitle(), *data->get(), Import(*data), WeightVar("w"));
 
    // Dataset d is now a dataset with one observable (x) with 1000 entries and a sum of weights of ~430K
    wdata.Print();

tutorials/roofit/rf403_weightedevts.py

@@ -26,7 +26,7 @@
 p0 = ROOT.RooPolynomial("px", "px", x)
 
 # Sample 1000 events from pdf
-data = p0.generate({x}, 1000)
+data = p0.generate(x, 1000)
 
 # Calculate weight and make dataset weighted
 # --------------------------------------------------
@@ -35,14 +35,14 @@
 wFunc = ROOT.RooFormulaVar("w", "event weight", "(x*x+10)", [x])
 
 # Add column with variable w to previously generated dataset
-w = data.addColumn(wFunc)
+data.addColumn(wFunc)
 
 # Dataset d is now a dataset with two observable (x,w) with 1000 entries
 data.Print()
 
-# Instruct dataset wdata in interpret w as event weight rather than as
-# observable
-wdata = ROOT.RooDataSet(data.GetName(), data.GetTitle(), data, data.get(), "", w.GetName())
+# Create a new dataset wdata where w is interpreted as event weight rather than
+# as observable
+wdata = ROOT.RooDataSet(data.GetName(), data.GetTitle(), data.get(), Import=data, WeightVar="w")
 
 # Dataset d is now a dataset with one observable (x) with 1000 entries and
 # a sum of weights of ~430K
@@ -100,10 +100,10 @@
 genPdf = ROOT.RooGenericPdf("genPdf", "x*x+10", [x])
 
 # Sample a dataset with the same number of events as data
-data2 = genPdf.generate({x}, 1000)
+data2 = genPdf.generate(x, 1000)
 
 # Sample a dataset with the same number of weights as data
-data3 = genPdf.generate({x}, 43000)
+data3 = genPdf.generate(x, 43000)
 
 # Fit the 2nd order polynomial to both unweighted datasets and save the
 # results for comparison