Combining TH1 similar to TMultiGraph example

ROOT
#1

Is there a feasible way to combine multiple TH1s into a single plot similar to the TMultiGraph example shown here: (https://root.cern.ch/doc/master/classTMultiGraph.html)

My issue is the resulting plot is heavily convoluted when drawing using ‘same’. The generation of the TH1s is handled by a separate function so access to the Fill aspect is not possible. TStackedHisto is not what I am looking for, each TH1 should be independent.

Thank you kindly,
WillPainter

ROOT Version: 6.09/03
Platform: Ubuntu 16.04 LTS
Compiler: linuxx8664gcc

#2

Maybe a THStack drawn with “NOSTACK” or “NOSTACKB” is what you want.

Note also that you can easily create a TGraphErrors or a TGraph from your histogram.

#3

Thanks kindly,
By ‘create a TGraphErrors or a TGraph from histogram’ do you mean generate a TFit and the plot it with the corresponding parameters? Or is there another method that retains the bin structure of a TH1 in a TGraph?

#4

By construction TGraph are un-binned objects.

#5

Yes, but a single point ‘amplitude’ for each bin could be extracted (I do not know how to do this. GetBinContent() in a loop over the axis range?) then the central value of each bin and the amplitude would provide the same structure that would be lost in fitting. Is this feasible?

#6

Yes you can do that: you define the x value of each point equal to the bin center and the y value as the bin content. But you will loose the concept of bin

#7

Thank you, I will try this. Maybe the bin structure could be retained by storing the amplitude (y) twice. Once with x=BinCenter-BinWidth/2 and once with x=BinCenter+BinWidth/2, plotting with option “L” (no “P”) and a second function along the y=0 line, filling the area between. I think this should still look like a TH1 but be a TGraph.
Thanks for your assistance.

#8

But to do that the best is really to use a THStack and plot it with option option NOSTACK … (as @Wile_E_Coyote said ) it is exactly what you are looking for… no need to go to graphs.

#9

It is not quite what I need as the overlapping region of multiple semi-Gaussian distributions becomes very convoluted. My goal is to separate the different TH1s along the Z direction so they are comparable without overlapping each other.

#10

Histograms in a thstack plotted as lines with option nostack is exactly the same as multigraph. Of course do what you want. I was just pointing to what, seems to me, is much simpler

#11

Filling Tgraphs drawn with Draw(“L3D”) seems to be incompatible. ALF_L3Dmultigraph.pdf (27.1 KB)
ALFmultigraph.pdf (17.7 KB)
Histo0.pdf (14.2 KB)
Histo1.pdf (14.2 KB)
Histo2.pdf (14.1 KB)
Histo3.pdf (14.2 KB)
Histo4.pdf (14.2 KB)
MultiGraphL3Dtest.cpp (2.5 KB)

#12

Incompatible with what ?

#13

The usual method to shade the enclosed area using SetFillColor or SetFillColorAlpha and “F” in the draw options does not result in a filled area. I have tried adding an additional point at the end of the vectors so the first and last points are the same. Enclosing the area however this does not help.

#14

When drawn in 3D the multigraphs are always drawn with lines.

#15

Is there a way to override this draw function?

#16

The function doing this plot is:
https://root.cern/doc/master/TMultiGraph_8cxx_source.html#l01361

#17

Ok. I do not see a way to implement this functionality with my level of ROOT proficiency. Can I submit a request for the “L3D” Draw() mode be made compatible with the other TGraph Draw() modes, specifically “F”?

#18

You can create a Jira ticket asking for it.

#19

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