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--- root:loadtext [2010/11/12 15:09] – nchiap
+++ root:loadtext [2010/11/15 17:17] (current) – nchiap
@@ Line 34: / Line 34: @@
 You can extend this idea to plot all histograms in an unknown tree.
 The following code reads a tree form a datafile with a arbitrary number of columns
-and creats a histogram for each of them.
+and creates a histogram for each of them.
 <code C++>
+        /** Load Data into Tree **/
+        TTree *T = new TTree("myT","data from ascii file");
+        Long64_t nlines = T->ReadFile(filename);
+        /** Attache memory to tree **/
+        Int_t nCols = T->GetListOfBranches()->GetEntries();
+        std::vector<Float_t> entry(nCols, 0);
+        for (Int_t i=0; i < nCols; i++) {
+          TString colName = T->GetListOfBranches()->At(i)->GetName();
+          T->SetBranchAddress(colName.Data(),&(entry[i]));
+        }
+        /** Calculate binning **/
+        Int_t nentries = (Int_t)T->GetEntries();
+        T->GetEntry(0);
+        Float_t first = entry[0];
+        T->GetEntry(1);
+        Float_t second = entry[0];
+        Float_t step = second-first;
+        first = first - step/2;
+        Float_t last = first+step*(nlines);
+        /** Create Histograms **/
+        TH1F *h;
+        TObjArray histograms;
+        for (Int_t i = 0; i < nCols; i++) {
+          TString hName = Form("hist%d",i);
+          if (i == 1) {
+            h = new TH1F(hName,histTitle,nlines,first,last);
+          } else {
+            h = new TH1F(hName,"",nlines,first,last);
+          }
+          histograms.AddLast(h);
+        }
+        /** Fill Histograms **/
+        for (Int_t i=0;i<nentries;) {  // increment inside loop
+          T->GetEntry(i);
+          i++;
+          for (Int_t col = 1; col < nCols; col++) {
+                  h = dynamic_cast<TH1F*>(histograms[col]);
+                  h->SetBinContent(i, entry[col]);
+          }
+        }
 </code>

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