Draw selection with float value


I have a peculiar situation; When I use Draw selection option with a branch of “int” type, int count = Tree->Draw(“y:x2”, “x1==int”, “goff”); its works;

When I take a float (decimal) value branch, for instance
int count = Tree->Draw(“y:x2”, “x3==0.08”, “goff”);

no entries (incorrect of course); Any ideas,

thanks, Damir

ROOT Version: 6
Platform: Linux
Compiler: gcc 6.3.0

So you don’t get any output either if you do this?


If not, can you post the output of Tree->Print() ? To get nice formatting like my line above, when you paste here enclose the output lines within three single left quote marks (```), see here.

I assume it’s:
(double(0.08)) - (float(0.08))
Long64_t count = Tree->Draw("y:x2", "abs(x3 - 0.08) < (0.08 * 1.e-5)", "goff"); // 1.e-5 = "5 significant decimal digits precision"

works! very nice; Different topic why this sensitivity to float, because when I do Scan I do see 0.08 going to 0.07999 which was the cause of the issue,

cheers, Damir

If you want “0.07999” to be included, you should use something like (0.08 * 2.e-4), which means slightly less than 4 significant decimal digits precision (actually, something like 1.26e-4 instead of 2.e-4 could be sufficient).

See also:

cppreference.com -> C++ -> C++ language -> Basic Concepts -> Fundamental types

Wikipedia - Floating point

“Floating point - Representable numbers, conversion and rounding”

C/C++ “double” usually means: Double-precision floating-point format

C/C++ “float” usually means: Single-precision floating-point format

This topic was automatically closed 14 days after the last reply. New replies are no longer allowed.