Eval (query directive) - Revision history

Olli: /* Examples */

2013-11-29T13:11:27Z

‎Examples

2013-11-29T13:08:08Z

2009-08-25T11:03:57Z

‎Examples

2009-08-25T10:54:23Z

‎Examples

2009-08-25T10:02:55Z

‎Examples

2009-08-25T08:24:35Z

‎Description

2009-08-25T08:23:47Z

‎Constructor

2009-08-25T08:23:08Z

‎Examples

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2009-08-21T12:44:58Z

@@ Line 36: / Line 36: @@
   importPackage(org.wandora.query2);
-  new Expr("\"BaseName: \"+val")
+  new Eval("\"BaseName: \"+val")
   .from(new BaseName())
   .from(new Instances())

@@ Line 12: / Line 12: @@
 The ''Eval'' directive contained in ''dir'' variable has some useful methods.
-* ''set(String key,Object value)'' Sets an object in an internal hash map. You can use this to store anything you like. It is cleared between queries. Ff the same sub-query is executed several times in a query, it will retain its contents between each execution.
+* ''set(String key,Object value)'' Sets an object in an internal hash map. You can use this to store anything you like. It is cleared between queries. If the same sub-query is executed several times in a query, it will retain its contents between each execution.
 * ''get(String key)'' Gets an object from the internal hash map.
 * ''empty()'' Returns an empty result iterator.
-The value on the last lime of the script is the return value of the script. it can be one of four things:
+The value on the last line of the script is the return value of the script. it can be one of four things:
 * A ''ResultIterator'' object which is returned as is as the result of the directive. It may be an empty iterator or iterate through any number of rows

@@ Line 78: / Line 78: @@
+  )
-Next example has a much more complex script in the ''Eval'' directive. It selects all players in all associations of the input that do not merge with the input topic (i.e. are not the same topic as input). Then we use ''Unique'' to remove duplicates, count the number of rows and then take average over all topics in the topic map. In the end we get the average number of topics each topic in the topic map is connected to by associations.
+Next example has a much more complex script in the ''Eval'' directive. It selects all players in all associations of the input that do not merge with the input topic (i.e. are not the same topic as input). Then we use ''Unique'' to remove duplicates, count the number of rows and then take average over all topics in the topic map. In the end we get the average number of topics each topic in the topic map is connected to by associations. You can use back-slash character to continue a string (the script itself) to next line.
   importPackage(org.wandora.query2)
@@ Line 85: / Line 85: @@
       new Unique(
         new Eval("\
   topic=input.getActiveValue();\
   as=topic.getAssociations();\
@@ Line 100: / Line 99: @@
     }\
   }\
-  ret\
+  ret;\
         ")
+      )

@@ Line 76: / Line 76: @@
       ).from(new Instances())
+    )
+  )
 [[Category:Query directives]]

@@ Line 63: / Line 63: @@
   ).as("#eval").from(new Instances().as("#instance"))
-Another way to store information is using the param object. Here we pass a java script table ''{sum:0}'' to ''Eval'' constructor and then access it in the script using ''param''.
+Another way to store information is using the param object. Here we pass a java script table ''{sum:0}'' to ''Eval'' constructor and then access it in the script using ''param''. Note that it is easier to do the same thing as this query using [[Sum (query directive) |Sum]] directive.
   importPackage(org.wandora.query2);

@@ Line 8: / Line 8: @@
 * ''val'' contains the active value of the input row.
 * ''dir'' contains the ''Eval'' directive itself.
 The ''Eval'' directive contained in ''dir'' variable has some useful methods.

@@ Line 26: / Line 26: @@
 == Constructor ==
-Eval()
+Eval(String script)
 == Examples ==

@@ Line 3: / Line 3: @@
 Evaluates a script. The script can do simple modifications to the input value or be arbitrarily complex.
-The script context is initialized with three values.
+The script context is initialized with some values.
 * ''input'' contains the entire input row.
 * ''context'' contains the query context, you can get the active topic map from it.
 * ''val'' contains the active value of the input row.
 The value on the last lime of the script is the return value of the script. it can be one of four things:
@@ Line 15: / Line 22: @@
 * Any other object which will be added in the input row with the default column name.
-In most cases the last option is sufficient and is by far the easiest to implement.
+In most cases the last option is sufficient and is by far the easiest to implement. Note that returning null falls under the last case and it will produce a result row with a null value. Easiest way to return nothing, that is zero result rows, is to use the ''empty'' method in the ''dir'' variable. Just doing ''dir.empty()'' creates a new empty ''ResultIterator''.
 == Constructor ==
@@ Line 29: / Line 36: @@
   .from(new BaseName())
   .from(new Instances())
 [[Category:Query directives]]