Get specific value form 2D-array

ROOT
1

Hi,

I have several root files and want to get value from 2D-array to make a histogram.
But I only need [1~6]x[1~3], [1~6]x[1~3], [1~6]x[1~3] data of my 9x5 array.
First I chain all of them first, then do:
mychain->SetBranchAddress("dth",&dth); Long64_t nentries = mychain->GetEntries(); for(Int_t i=0;i<nentries;i++){mychain->GetEntry(i);.......
Then I can’t find out anyway to do it…Should I store it into Vector, or is there another faster and better way to do?

Thanks.

2

What is your favorite way of access the data (i.e. for example when you don’t need the filtering) [Asking so we can tweak that method rather introducing a new one].

Cheers,
Philippe.

3

Hi,

I used:

  mychain->SetBranchAddress("dth",&dth);
  vector<Double_t> xpos;
  vector<Double_t> ypos;
  vector<Double_t> zpos;
  
  for(Int_t i=0;i<nentries;i++){
    mychain->GetEntry(i);
    
    for(Int_t j=1,k=1,l=1;j<7,k<7,l<7;i++,j++,l++){
    xpos.push_back(dth[j][1]);
    ypos.push_back(dth[k][2]);
    zpos.push_back(dth[l][3]);
    }
  }

  TH1D *histo = new TH1D(xpos.data());

Then it turned out:

Warning: Illegal numerical expression 7,k eldth2.cpp:55:
Warning: Illegal numerical expression 7,k eldth2.cpp:55:
Warning: Illegal numerical expression 7,l eldth2.cpp:55:
Error: Array index out of range dth -> [46]  valid upto dth[8][4] eldth2.cpp:56:
*** Interpreter error recovered ***
4

Rather than

j<7,k<7,l<7;

you meant

j<7 && k<7 && l<7;

Cheers,
Philippe

5

It’s really dumb that I didn’t notice it…Thanks!
But after I correct it I got:

Error: Can't call vector<double,allocator<double> >::data() in current scope eldth2.cpp:60:
Possible candidates are...
(in vector<double,allocator<double> >)
*** Interpreter error recovered ***
6

This is odd and seems like a bug in CINT. I recommend that either compile the scrip with ACLiC or upgrade to using ROOT v6.10.

Cheers,
Philippe.

7

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