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--- root:loadtext [2010/11/09 16:33] – created nchiap
+++ root:loadtext [2010/11/15 17:17] (current) – nchiap
@@ Line 2: / Line 2: @@
 To read data from a text file into a tree all you need are the following two lines
 <code C++>
-  TTree *myTree = new TTree("ntuple","data from ascii file");
+  TTree *myTree = new TTree("mytree","data from ascii file");
   Long64_t nlines = myTree->ReadFile(filename,"col1:col2:col3");
+</code>
+=== Dynamic Branche Names ===
+If you do not give the structure, the first line of your file must contain the tree definition
+<code text input.csv>
+bin:hist1:hist2
+12 13
+[...]
+</code>
+To use this tree you then need to get the branch names
+<code C++>
+  TTree *myTree = new TTree("mytree","data from ascii file");
+  Long64_t nlines = myTree->ReadFile(filename);
+  TString col0Name = T->GetListOfBranches()->At(0)->GetName();
+  TString col1Name = T->GetListOfBranches()->At(1)->GetName();
+  TString col2Name = T->GetListOfBranches()->At(2)->GetName();
+  Float_t bin,hist1,hist2;
+  T->SetBranchAddress(col0Name.Data(),&bin);
+  T->SetBranchAddress(col1Name.Data(),&hist1);
+  T->SetBranchAddress(col2Name.Data(),&hist2);
+</code>
+=== Dynamic Tree Structure ===
+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 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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