A way to extend the low bin edge of the lowest bin and save as .root file?

[trenta_coollime]

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ROOT Version: 6_10
Platform: Ubuntu 16.04
Compiler: gcc 630

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Hi, I have a rootfile, which has a 2D histogram with lowest bin (20,25).

Is there an easy way to extend the lower threshold such that the bin has range of (12,25) with same bincontent?

I guess one can literally use setbincontent, getbincontent functions for every single entry to recreate entire 2Dhist.

However, I expect that experts would know a much faster shortcut for my situation where I need to change only one bin’s lower threshold and save that as root file.

I appreciate your expert comments and advice

Thank you so much.

Trentacoollime.

[Wile_E_Coyote]

Are the axes of your histogram “fix bin size” or “variable bin size”?

Try (if you want to modify the “x axis”):

your_histogram->GetXaxis()->IsVariableBinSize()

If the axis is a “fix bin size” then, you will need to create a new histogram with correct axes ranges.

If the axis is a “variable bin size” then, you can simply execute (if you want to modify the “x axis”):

(*(TArrayD*)your_histogram->GetXaxis()->GetXbins())[0] = 12.; // the lowest edge

Afterwards, you need to execute:

// one must set the new proper "xmin" and "xmax" for this axis
your_histogram->GetXaxis()->SetLimits(
  (*your_histogram->GetXaxis()->GetXbins())[0],
  (*your_histogram->GetXaxis()->GetXbins())[your_histogram->GetNbinsX()]
);