updated the documentation (README) to include examples with iterator

README.md

@@ -65,6 +65,59 @@ Output:
 
 <img src="https://github.com/gavalian/hipo/blob/master/documents/screenshots/histogram_vz.png" width="800">
 
+## Iterators
+
+Iterators can be used to read through bank. There are several ways to construct iterators, through expressions and
+through lambda functions. Here is an example with expressions:
+
+```c++
+  hipo::reader   r(file);
+  hipo::banklist list = r.getBanks({"REC::Particle","REC::Event"});
+  while( r.next(list)){
+      hipo::iterator it = hipo::iterator::reduce(list[0],"charge!=0");
+      for(it.begin(); !it.end(); it.next()){
+        printf("\t pid [%d] = %d\n",it.index(), list[0].getInt(0,it.index()));
+      }
+  }
+```
+
+Here is an example with lambda function:
+
+```c++
+  hipo::reader   r(file);
+  hipo::banklist list = r.getBanks({"REC::Particle","REC::Event"});
+  std::function charged = [](hipo::bank &b, int row) { return b.getInt("charge",row)!=0 ? 1.0 : 0.0;};
+
+  while( r.next(list)&&counter<350){
+    hipo::iterator it = hipo::iterator::reduce(charged,list[0]);
+    for(it.begin(); !it.end(); it.next()){
+      printf("\t pid [%d] = %d\n",it.index(), list[0].getInt(0,it.index()));
+    }
+  }
+```
+
+Iterators can be used also to get indicies of the refernce bank. For example:
+
+```c++
+  hipo::reader   r(file);
+  hipo::banklist list = r.getBanks({"REC::Particle","REC::Calorimeter"});
+
+  while( r.next(list)&&counter<350){
+    int status = list[0].getInt("status",0);
+    if(list[0].getInt(0,0)==11&&abs(status)>=2000&&abs(status)<3000){
+      hipo::iterator it = hipo::iterator::link(list[1],0,1);
+      double energy = 0.0;
+      for(it.begin(); !it.end(); it.next()){
+        energy += list[1].getFloat("energy",it.index());
+      }
+      printf("total energy = %f\n",energy);
+    }
+  }
+```
+
+In the example above, the link function will return an iterator for the bank "REC::Calorimeter"
+where the column number 1 (which is "pindex") has a value of 0. Then by itarating over the returned
+indicies the total energy can be calculated.
 
 ## Analysis
 

examples/histograms.cc

@@ -166,23 +166,17 @@ void example7(const char *file){
 }
 
 void example8(const char *file){
+
   hipo::reader   r(file);
   hipo::banklist list = r.getBanks({"REC::Particle","REC::Event"});
-  int counter = 0;
-
-  std::function charged = [](hipo::bank &b, int row) {
-    int charge = b.getInt("charge",row);
-    if(charge!=0) return 1.0; return 0.0;
-  };
+  std::function charged = [](hipo::bank &b, int row) { return b.getInt("charge",row)!=0 ? 1.0 : 0.0;};
 
+  int counter = 0;
   while( r.next(list)&&counter<350){
     counter++;
     hipo::iterator it = hipo::iterator::reduce(charged,list[0]);
     list[0].show();
     it.show();
-      //for(it.begin(); !it.end(); it.next()){
-      //  printf("\t pid [%d] = %d\n",it.index(), list[0].getInt(0,it.index()));
-      //}
   }
 }