[Pig Wiki] Update of "UserDefinedOrdering" by OlgaN

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The following page has been changed by OlgaN:
http://wiki.apache.org/pig/UserDefinedOrdering

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  public int compare(Tuple t1, Tuple t2) { ... }
  
  }
+ }}}
+ 
+ == Examples ==
+ 
+ === Example 1 ===
+ 
+ This code implements string-based comparator to produce the data in the 
descending order.
+ 
+ {{{
+ package org.apache.pig.test;
+ 
+ import org.apache.pig.data.Tuple;
+ import org.apache.pig.ComparisonFunc;
+ 
+ public class OrdDesc extends ComparisonFunc {
+     // this is a simple example - more complex comparison will require
+     //   breakout of the individual values. I suggest you'll have
+     //   to convert "catch(IOException e) to RuntimeException('msg', e)"
+     public int compare(Tuple t1, Tuple t2) {
+         return t2.compareTo(t1);
+ }
+ }}}
+ 
+ === Example 2 ===
+ 
+ This code implements numeric comparator to produce the data in the descending 
order. 
+ Note that you need a recursive compare to account for arbitrary complex 
tuples.
+ 
+ {{{
+ package org.apache.pig.test;
+ 
+ import java.io.IOException;
+ 
+ import org.apache.pig.data.DataAtom;
+ import org.apache.pig.data.Datum;
+ import org.apache.pig.data.Tuple;
+ import org.apache.pig.ComparisonFunc;
+ 
+ public class OrdDescNumeric extends ComparisonFunc {
+     public int compare(Tuple t1, Tuple t2) {
+         try {
+             for (int i = 0; i < t1.arity(); i++) {
+                 Datum d1 = t1.getField(i);
+                 Datum d2 = t2.getField(i);
+                 int comp;
+                 if (d1 instanceof DataAtom) {
+                     comp = compare((DataAtom)d1, (DataAtom)d2);
+                 } else {
+                     comp = compare((Tuple)d1, (Tuple)d2);
+                 }
+                 if (comp != 0) {
+                     return comp;
+                 }
+             }
+             return 0;
+         } catch (IOException e) {
+             throw new RuntimeException("Error comparing keys in 
OrdDEscNumeric", e);
+         }
+     }
+ 
+     private int compare(DataAtom a1, DataAtom a2) throws IOException {
+         double num1 = a1.numval();
+         double num2 = a2.numval();
+         if (num2 > num1) {
+             return 1;
+         } else if (num2 < num1) {
+             return -1;
+         }
+         return 0;
+     }
+ }
+ 
  }}}
  
  == Semantics ==