How to take average of vector values

Hi all,
I need a way to average all the values in a vector, and I am using std::accumulate right now with no success…

Here is a snippet of my code, the bold is the use of the vector v:

std::vector<double> v;
for(int g=0; g<8257; g++){

      for (Long64_t j=0; j< 1000; j++) { 
              Long64_t centry = chchain->LoadTree(j);
                    if (centry <0 ) break;
                   cb = chchain->GetEntry(j); cbytes += cb;

if (g==_ch){

double sum = std::accumulate(v.begin(),v.end(),0.0)
double mean = sum/941;

… but the histogram doesn’t fill… why is this?
Is there something I am doing wrong, or something else I can try?


    double sum = std::accumulate(v.begin(), v.end(), 0.0);
    double mean = sum / 941.;
    avg_compvch->Fill(g, mean);

still empty histogram :confused:

See what you get when you try:

_ch vs _ch_compression is actually a different histogram that I also make in my script, and it comes out fine.

Well, you do not show your complete source code so I can only hope that you do “SetBranchAddress” for both branches (i.e. “_ch” and “_ch_compression”).
If yes, I think you could simplify your code:

TH1D *avg_compvch = new TH1D("avg_compvch", "avg_compvch", 8257, 0, 8257);
for (Long64_t j = 0; j < 1000; j++) {
  Long64_t centry = chchain->LoadTree(j);
  if (centry < 0 ) break;
  std::cout << j << " : " << _ch << " : " << _ch_compression << std::endl;
  avg_compvch->Fill(_ch, _ch_compression);
avg_compvch->Scale(1./941.); // calculate "means"

A post was split to a new topic: Average of histograms