Problem with initializing an array of TH1D objects

ROOT
1

Dear Root Experts,

I have the following problem: I have an array of TH1D objects and I want to use the same style TH1D to initialize them all. If I do this initialization explicitly by specifying the index of each object in the array than everything is perfectly fine (see attached macro withoutLoop.C), but if I use the loop, than the code crashes (see attached macro withLoop.C).

Can anybody suggest what I am missing here?

I am using ROOT 5.24/00 (tags/v5-24-00@29258, Jul 01 2009, 12:22:53 on linuxx8664gcc)

Cheers,
Ante
withLoop.C (250 Bytes)
withoutLoop.C (286 Bytes)

2

I suggest to use one of the 2 methods shown in the example below

Rene

[code]void withLoop()
{
TH1D style(“styleName”,“styleTitle”,1,0,1);
TH1D *histArray[2];

for(Int_t i=0;i<2;i++) {
histArray[i]= (TH1D*)style.Clone(Form(“styleName%d”,i));
cout<<(histArray[i])->GetName()<<endl;
}
}
void withLoop2() {
TH1D style(“styleName”,“styleTitle”,1,0,1);
TH1D *histArray[2];

for(Int_t i=0;i<2;i++) {
histArray[i]= new TH1D(style);
histArray[i]->SetName(Form(“styleName%d”,i));
cout<<(histArray[i])->GetName()<<endl;
}
}
[/code]

3

Dear Rene,

Thanks for your quick and helpful reply!

However, I have one additional small question related to the arrays of TH1D objects:

Namely, if I have:

TH1D *histArray[2];
TList *list;

and I want to add all elements of histArray to the list without looping, I cannot of course naively use

list->Add(histArray);

because that is equivalent to

list->Add(&histArray[0]);

Could you suggest how to proceed here?

Thanks you very much for your time.

Cheers,
Ante

4

You can insert directly your histograms inside the list as shown below. You can add a Tlist to a TList, but not insert the objects of a list into another list.

Rene

[code]void withLoop()
{
TH1D style(“styleName”,“styleTitle”,1,0,1);
TList listH;

for(Int_t i=0;i<2;i++) {
TH1D h= (TH1D)style.Clone(Form(“styleName%d”,i));
listH.Add(h);
cout<GetName()<<endl;
}
listH.ls();
}
[/code]

5

Dear Rene,

Thanks for your reply!

I know that I can add histograms directly to TList in the way you have outlined or that I can have nested TLists, but my question was going in a slightly different direction.

Namely, if I have an array of histograms and a list

TH1D *histArray[n];
TList *list;

than I thought (naively) that perhaps it is possible to call method Add() of TList in the following way (or something similar)

list->Add([] histArray);

and than the list ‘would know’ that I want to store all entries of histArray, without a need to loop over all entries of histArray in my code. This would become very handy for multi-dimensional arrays.

In principle the analogous syntax could work if I want to access entries of histArray from the list, but I do not claim that I really understand all possible issues and sideeffects here :wink:

So I will stick to what is available now in Root and organize my histograms in the nested lists, instead of arrays.

Thanks once again for your replies.

Cheers,
Ante