Import a TH1 of Variable binning into a RooDataHist

[fsoomro]

Given the absence of a reply to this and also this previous thread by iostrovskiy

Plotting RooDataHist with uneven binning

Hi! There is a RooDataSet that I want to convert into a RooDataHist with particular binning. So I create a RooDataHist with uneven binning using ::RooDataHist(name,title,vars,myBinning), and then do ::add(dataset) I can see that the binning was set correctly and all bins have ::weight() just like I expected. But I can’t find a way to plot it such that it shows actual number of events in each bin. Instead, as you can see in the attached snapshot, it plots something like events density. Is th…

I would like to ask the developers to make really clear the subtlety of the way to importing a TH1 into a RooDataHist:
Import (TH1*, kFALSE)
It is not at all made obvious that with uneven binning one should not use the simple constructor with out the ‘import’ option. Moreover, there is not one example in the tutorials with uneven binning.

Secondly, the point of plotting a RooDataHist with uneven binning is also non trivial and has cost me (and I believe many) much time and pain.
The fact that the RooHist object (which actually does the plotting) respects your correctForBinWidth choice depending on your choice of errors is a bug. It does not respect your correctForBinWidth choice if you chose the default errors, only if you specify DataError(RooAbsData::SumW2) while plotting will it respect the correctForBinWidth choice.