//Chad Harrington 3/23/2015

//Skim a TTree

#include "TFile.h"

#include "TTree.h"

using namespace std;

void skim(){

int numSkip = 1013;

TFile* file = TFile::Open("bigFile.root");

TTree* tree = (TTree*) file->Get("T");

Long64_t nEntries = tree->GetEntries();

ULong64_t event;

tree->SetBranchAddress("event", &event);

tree->SetBranchStatus("*",1);

TFile *newfile = new TFile("skimmedTree.root","recreate");

TTree *newtree = tree->CloneTree(0);

for (Long64_t n=0; n<nEntries; n++) {

tree->GetEntry(n);

if (event % numSkip == 0) newtree->Fill();

}

newtree->Print();

newfile->Write();

delete file;

delete newfile;

}