Multiple projections to a 1D histogram from multiple files

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1

I’m trying to project into a histogram (from a Tree) multiple times from different files.
It does not work, but seems to erase the histogram add each Project. Why?

2

It (re)creates an automatic temporary histogram called “htemp” (which is usually owned by the current canvas / pad).
You need to draw your projections in different canvases / pads or you need to “save” your projections in histograms with different names.

3

Thanks! You mean there is no way to actually add to a an existing histogram by projecting? I have to add up many histograms, one for each projection?

4

You can do it using, for example, something like this:

some_tree_1->Draw("some_leaf >> my_histo"); // (re)creates "my_histo"
some_tree_2->Draw("some_leaf >>+ my_histo"); // adds entries to "my_histo"
some_tree_3->Draw("some_leaf >>+ my_histo"); // adds entries to "my_histo"
5

Thanks. That way is more practical.

6

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