Dynamically create histograms

ROOT
1

Hi ROOTers,
I am reading a data file, and some of the events are bad. I need to plot the bad ones in a TH1F histogram, and save them to a root file. Now, if I knew how many bads I will have, I would just create an array of histos like

TH1F *hist[10]; for (int i=0; i<11; i++) hist[i] = new TH1F(Form("blah[%d]",i),"blah",4096, 0, 4095);

But the problem is I don’t know how many bads I will have. Is there a way to create histograms on the fly, as soon I encounter a bad flag I do something similar to

if (bad)
TH1F *hist[EventNumber]=new TH1F(Form("blah[%d]",EventNumber),"blah",4096, 0, 4095) ;
for(int ii=0; ii<=256 ; i++) hist[EventNumber]->Fill(ii,eventdata[ii]);

Thanks!
Artur

2

OK I figured it. I use of TH1F’s.

3

why not to use ROOT classes like TList, TObjArray, etc?
root.cern.ch/root/htmldoc/TList.html

4

[quote]why not to use ROOT classes like TList, TObjArray, etc?
root.cern.ch/root/htmldoc/TList.html[/quote]

Because C++ programmer should prefer C++ standard library where possible. Of course, if someone wants to hold THs in a container (by value)and frequently remove some elements, vector is bad choice.

5

Well, yeah, the vector does what I need.
Thanks guys!

6

[quote]Well, yeah, the vector does what I need.
Thanks guys![/quote]

Yes, but if you have std::vector and want to remove some elements, it can be expensive - a lot of copying == possible dynamic allocation.

7

[quote=“tpochep”][quote]Well, yeah, the vector does what I need.
Thanks guys![/quote]

Yes, but if you have std::vector and want to remove some elements, it can be expensive - a lot of copying == possible dynamic allocation.[/quote]
Yes, one knows better :unamused: what he wants :wink:. He wants to remove something doesn’t he?
One knows better he wants std::list
However the ROOTForum eats :blush: the symbol “star”, that’s confusing. As result one reads “value” where the guy said “pointer” :bulb:

8

I am using a

and then

if (bad) badCounter++; for(int ii=0; ii<=256; ii++) BadEvent->Fill(ii,eventdata[ii]); BadHistos.push_back(BadEvent);
is that a bad idea to do it this way? I mean considering I don’t need to access, modify or remove any of the histos, except for writing them to the root file.

9

It is Ok.
However if you choose using the ROOT container you may have written the entire container rather each histogram separately in loop.
Another comment. I think you may avoid the counter. The container “counts” its own size anyway.
I hope the real code does

if (bad) { badCounter++; bla . . . . bla BadHistos.push_back(BadEvent); }

10

Hello, Valeri.

[quote=“fine”]
However the ROOTForum eats :blush: the symbol “star”, that’s confusing. As result one reads “value” where the guy said “pointer” :bulb:[/quote]

Yes, you are right, for example in my reply somewhere I wrote

static_cast<pointer_to_TGeoSphere>(vol->GetShape()) and the result in the forum was static_cast<TGeoSphere>(vol->GetShape()).

11

[quote=“fine”]
I hope the real code does

if (bad) { badCounter++; bla . . . . bla BadHistos.push_back(BadEvent); }[/quote]
Yeah, that’s what it does, sorry :blush: