Problem with zero value in the Histo TH2F

Roofit and RooStats
1

I’m sorry,
I have a problem to plot a list of values having “zero” value in a histogram TH2F.
For a Bin with value “0 - Zero” the histo don’t plot the color in the bin.
How can I manage this issue?
Kind regards,
Daniele

2

Hi Daniele,

In most cases ROOT does not plot 0 values.
In case of color plot it normally ignored. To tweak ROOT histogram painter, you can call:

hpxpy->SetMinimum(-1)

In such case 0 will be not minimum value and will be displayed with the color.

Regards,
Sergey

1 Like
4

Hi Sergey,
many thanks for your replay,
but in this case with minimum “-1”, I have a blue background because all Hist value = 0 and all Hist value not filled become blu.
I need to “mark” the bin, Lat/Long with “0” in (Blue or how is reported by the color scale), but only for the specific bin and the other must be undefined(White).
Kind regards,
Daniele

5

Hi Daniele,

If you want to mark only some specific bins, just set content slightly bigger than 0:

h2->SetBinContent(h2->GetBin(20,20), 0.01);

It will be shown with color.

Regards,
Sergey

6

Hi Sergey,
I already done this approach and works, but my teacher want “0”.
I thank you in advance for your support,
Regards,
Daniele.

7

There no possibility in ROOT to draw same bin content values with different colors.
Probably, just draw TBox at position you want:

TBox *b = new TBox(-1,-1,1,1);
b->SetFillColor(kBlue);
b->Draw();
10

We cannot make the difference between bins never filled and bins having content zero because the sum of all fills is zero. Can you provide a small example showing your problem ?

11

Hi Couet,
I solved the problem with a value 0,00001.
I had to put in an Histogram a set of value where the value of some bin was “0”.
For me “0” is different from no value.
I had a map 12 X 10(BIN), not completely filled, but some of this bin was “0” but for me “0” should be plotted.
For example:
Bin(1,2)=5; Bin(3,5)=3; Bin(2,4)=0; Bin(8,4)=0; Bin(10,6)=0;Bin(1,9)=20; and the other Bin=NULL;
I want to plot the content of Bin(2,4), Bin(8,4) …that are “0” but I don’t want to plot the others BIN=NULL.
If I use the method:
Draw(“COLZ”);
The Bin with value “0” doesn’t appear.
I solved with a value slightly more than 0.
Kind regards,
Daniele

12

Yes for ROOT value “0” or “not filled” is the same.

13

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