Changes between Version 15 and Version 16 of DatabaseBasedAnalysis/rootifysql

Timestamp:

08/05/18 20:22:56 (6 years ago)

Author:

tbretz

Comment:

--

DatabaseBasedAnalysis/rootifysql

@@ -6 +6 @@
 The idea of {{{rootifysql}}} is to conveniently request data from a MySQL database and write the contents returned into a tree in a root-file. Root trees offer a lot of nice features how to access the data fast and how to create plots easily.
 
-For details, please refer either to the Draw-function of TTree (e.g. https://root.cern.ch/doc/master/classTTree.html#a73450649dc6e54b5b94516c468523e45) or checkout the root user manual (https://root.cern.ch/guides/users-guide), in particular the section about '''Trees'''.
+For details, please refer either to the Draw-function of TTree (e.g. https://root.cern.ch/doc/master/classTTree.html#a73450649dc6e54b5b94516c468523e45) or checkout the root user manual (https://root.cern.ch/guides/users-guide), in particular the section about '''Trees'''. A mini-tutorial is given at the end of the page.
 
 In the following basic knowledge on C++, {{{root}}} and root trees is assumed.
@@ -476 +476 @@
 
 In case of success, {{{rootifysql}}} returns 0, a value>0 otherwise.
+
+== Analysis with root ==
+
+Here is a short example how to access the data from the root file, assuming a filename '''rootify.root''', the default tree name '''Result''' and two branches with name '''Col0''' and '''Col1'''
+{{{#!cpp
+void example()
+{
+    // Create chain for the tree Result
+    // This is just easier than using TFile/TTree
+    TChain c("Result");
+
+    // Add the input file to the
+    c.AddFile("rootify.root");
+
+    // Assume you want to convert Col1 from RAD to DEG
+    c.SetAlias("col1deg", "Col1*TMath::RadToDeg()");
+
+    // Plot Col0 if Col1>PI
+    new TCanvas;
+    c.Draw("Col0", "Col1>TMath::Pi()");
+
+    // Plot Col1 in degree versus Col0
+    new TCanvas;
+    c.Draw("Col0:col1deg", "");
+}
+}}}
+
+or
+
+{{{#!cpp
+void example()
+{
+    // Create chain for the tree Result
+    // This is just easier than using TFile/TTree
+    TChain c("Result");
+
+    // Add the input file to the
+    c.AddFile("rootify.root");
+
+    // All columns are stores as doubles
+    double col0, col1;
+
+    // Connect the variables to the coresponding leaves
+    c.SetBranchAddress("Col0", &col0);
+    c.SetBranchAddress("Col1", &col1);
+
+    for (int i=0; i<c.GetEntries(); i++)
+    {
+        // read the i-th event from the file
+        c.GetEntry(i);
+
+        cout << col0 << " " << col1 << endl;
+    }
+}
+}}}
+
+Assuming the code is written to '''example.C''', both are executed with {{{root example.C}}}. Instead of {{{Draw()}}} also {{{Select()}}} can be used to print the data to the console.
+
+For details, please refer either to the Draw-function of TTree (e.g. https://root.cern.ch/doc/master/classTTree.html#a73450649dc6e54b5b94516c468523e45) or checkout the root user manual (https://root.cern.ch/guides/users-guide), in particular the section about '''Trees'''.