Scope Instruction - Processor

PROCESS

 

The PROCESS statement is used to convert one RowSet to another RowSet.  Uses include:

• Transformations
• Adding/Removing columns
• Filtering data
• Expanding data

Syntax

All PROCESS statements require:

• PROCESS [input]
• PRODUCE column(s)
• USING processor

Additionally, users can supply a WHERE or HAVING statement to either filter the input or output.

Example (1)

This is taken from the Processor page.

PROCESS

PRODUCE A,B,C,D

USING MyProcessor(-a);

What this is saying is:

1. Input the RowSet produced by the previous command
2. Output the columns      "A", "B", "C", and "D" with types      determined by MyProcessor
3. Use the Processor called      "MyProcessor" with the argument "-a" passed in

Example (2)

This example shows how to use WHERE and HAVING to filter the input and output Row objects.

PROCESS

PRODUCE A,B,C,D

USING MyProcessor(-a)

WHERE A != "scope"   //filter the output

HAVING A != "filter";   //filter the input

What this is saying is:

1. Input the RowSet produced by the previous command
2. Filter the input so that only rows having A not equal to      "filter" will be input
3. Output the columns      "A", "B", "C", and "D" with types      determined by MyProcessor
4. Use the Processor called      "MyProcessor" with the argument "-a" passed in
5. Filter the output so that only rows having A not equal to      "scope" will be output

Processors

 

Processors are used to take a RowSet and produce a RowSet.  Typically, they are used for:

• Transformations (i.e.      converting "A" to "Apple")
• Adding/removing columns
• Filtering (i.e removing Row objects where the first      column doesn't start with "A")

Internally, the WHERE and HAVING statements are implemented as Processors as well as many SELECT transformations.

Syntax

 

Let's look at the following script:

PROCESS

PRODUCE A,B,C,D

USING MyProcessor(-a)

WHERE A != "scope"

HAVING A != "filter";

What this is saying is:

1. Input the RowSet produced by the previous command
2. Filter the input so that only      rows having A not equal to "filter" will be further processed
3. Output the columns      "A", "B", "C", and "D"
4. Use the Processor called      "MyProcessor" with the argument "-a" passed in
5. Filter the output so that      only rows having A not equal to "scope" will be output

Note: The WHERE and HAVING clauses are optional, but the other clauses are required. 

Writing a Processor

 

Syntax

 

The easiest thing to do is to right-click in the editor and select Implement-Processor.  Here's an example of a Processor that will filter data:

#CS

public class SampleProcessor : Processor

{

         public override Schema Produces(string[] requestedColumns, string[] args, Schema inputSchema)

         {

               return inputSchema.Clone();

         }

  

         public override IEnumerable<Row> Process(RowSet input, Row outputRow, string[] args)

         {

               foreach(Row row in input.Rows)

               {

                      //  Filter rows

                      if (!row[0].String.StartsWith("A"))

                     {

                            row.Copy(outputRow);

                            yield return outputRow;

                     }

                     

               }

         }

}

#ENDCS

The two methods that need to be implemented are:

1. Produces
2. Process

Tips

• The outputRow object is      already handed to the Processor.
• Do not create your own Row      object
• Make your code efficient

转载于:https://www.cnblogs.com/yuqiyang/p/4536148.html