TAxis FixedToVariable and VariableToFixed proposal

[Wile_E_Coyote]

I would like to propose that two methods are added to the TAxis class: FixedToVariable and VariableToFixed.
So, an axis which was created as a “fixed bin sizes” one could be converted into a “variable bin sizes” one and the opposite.
Note: in case of the “VariableToFixed” method, we would not preserve bin widths, only the “low-edge”, the “upper-edge” and the number of bins would be used / preserved.

I guess I would like to have:

FixedToVariable(Double_t *xbins = 0)
FixedToVariable(Double_t xmin = 0., Double_t xmax = 0.)
VariableToFixed(Double_t xmin = 0., Double_t xmax = 0.)

If the user provides “xbins” or “xmin < xmax” then use them when calculating new bin edges / limits, otherwise calculate bin edges using the existing “low-edge” and “upper-edge” of the axis.

I don’t have any preference for what these methods should return, so maybe “void” is a good choice.

BTW. maybe you could also think about adding a “Scale” method:

Can we shift histogram for several channels?

I’m not sure if this is fully kosher, but suit yourself : #include "TAxis.h" #include "TH1.h" #include "TArrayD.h" Double_t ScaleX(Double_t x) { Double_t v; v = 10 * x + 100; // "linear scaling" function example return v; } Double_t ScaleY(Double_t y) { Double_t v; v = 20 * y + 200; // "linear scaling" function example return v; } Double_t ScaleZ(Double_t z) { Double_t v; v = 30 * z + 300; // "linear scaling" function example return v; } void ScaleAxis(TAxis *a, Double_t (…

[couet]

I guess @moneta can comment about your suggestion.

[ksmith]

Was @moneta able to comment on this? A similar question was asked:

TAxis::GetXbins does not always return bin edges

Hi, I am attempting to build a 2D histogram with bins defined in 1D histograms, but it appears that the TAxis::GetXbins function does not always produce an array of bin edges. For the case where a user provides the number of bins and min and max, the edge array is not produced. In the case where an array of edges is passed GetXbins works as expected. This makes generalized code that can read from either type of histogram much more difficult. Below is an example where the wrong bin edges are pro…