Rank Transformation Overview

By PenchalaRaju.Yanamala

Transformation type:ActiveConnected

You can select only the top or bottom rank of data with Rank transformation. Use a Rank transformation to return the largest or smallest numeric value in a port or group. You can also use a Rank transformation to return the strings at the top or the bottom of a session sort order. During the session, the Integration Service caches input data until it can perform the rank calculations.

The Rank transformation differs from the transformation functions MAX and MIN, in that it lets you select a group of top or bottom values, not just one value. For example, use Rank to select the top 10 salespersons in a given territory. Or, to generate a financial report, you might also use a Rank transformation to identify the three departments with the lowest expenses in salaries and overhead. While the SQL language provides many functions designed to handle groups of data, identifying top or bottom strata within a set of rows is not possible using standard SQL functions.

You connect all ports representing the same row set to the transformation. Only the rows that fall within that rank, based on some measure you set when you configure the transformation, pass through the Rank transformation. You can also write expressions to transform data or perform calculations.

Figure 17-1 shows a mapping that passes employee data from a human resources table through a Rank transformation. The Rank transformation only passes the rows for the top 10 highest paid employees to the next transformation.

Ranking String Values

When the Integration Service runs in the ASCII data movement mode, it sorts session data using a binary sort order.

When the Integration Service runs in Unicode data movement mode, the Integration Service uses the sort order configured for the session. You select the session sort order in the session properties. The session properties lists all available sort orders based on the code page used by the Integration Service.

For example, you have a Rank transformation configured to return the top three values of a string port. When you configure the workflow, you select the Integration Service on which you want the workflow to run. The session properties display all sort orders associated with the code page of the selected Integration Service, such as French, German, and Binary. If you configure the session to use a binary sort order, the Integration Service calculates the binary value of each string, and returns the three rows with the highest binary values for the string.

Rank Caches

During a session, the Integration Service compares an input row with rows in the data cache. If the input row out-ranks a cached row, the Integration Service replaces the cached row with the input row. If you configure the Rank transformation to rank across multiple groups, the Integration Service ranks incrementally for each group it finds.

The Integration Service stores group information in an index cache and row data in a data cache. If you create multiple partitions in a pipeline, the Integration Service creates separate caches for each partition.

Rank Transformation Properties

When you create a Rank transformation, you can configure the following properties:

Enter a cache directory.Select the top or bottom rank.Select the input/output port that contains values used to determine the rank. You can select only one port to define a rank.Select the number of rows falling within a rank.Define groups for ranks, such as the 10 least expensive products for each manufacturer.

Ports in a Rank Transformation

The Rank transformation includes input or input/output ports connected to another transformation in the mapping. It also includes variable ports and a rank port. Use the rank port to specify the column you want to rank.

The following table describes the ports in a Rank transformation:

Ports Number Required

Description

I Minimum of one

Input port. Create an input port to receive data from another transformation.

O Minimum of one

Output port. Create an output port for each port you want to link to another transformation. You can designate input ports as output ports.

V Not Required

Variable port. Can use to store values or calculations to use in an expression. Variable ports cannot be input or output ports. They pass data within the transformation only.

R One only Rank port. Use to designate the column for which you want to rank values. You can designate only one Rank port in a Rank transformation. The Rank port is an input/output port. You must link the Rank port to another transformation.

Rank Index

The Designer creates a RANKINDEX port for each Rank transformation. The Integration Service uses the Rank Index port to store the ranking position for each row in a group. For example, if you create a Rank transformation that ranks the top five salespersons for each quarter, the rank index numbers the salespeople from 1 to 5:

RANKINDEX SALES_PERSON SALES

1 Sam 10,000

2 Mary 9,000

3 Alice 8,000

4 Ron 7,000

5 Alex 6,000

The RANKINDEX is an output port only. You can pass the rank index to another transformation in the mapping or directly to a target.

Defining Groups

Like the Aggregator transformation, the Rank transformation lets you group information. For example, if you want to select the 10 most expensive items by manufacturer, you would first define a group for each manufacturer. When you configure the Rank transformation, you can set one of its input/output ports as a group by port. For each unique value in the group port, the transformation creates a group of rows falling within the rank definition (top or bottom, and a particular number in each rank).

Therefore, the Rank transformation changes the number of rows in two different ways. By filtering all but the rows falling within a top or bottom rank, you reduce the number of rows that pass through the transformation. By defining groups, you create one set of ranked rows for each group.

For example, you might create a Rank transformation to identify the 50 highest paid employees in the company. In this case, you would identify the SALARY column as the input/output port used to measure the ranks, and configure the transformation to filter out all rows except the top 50.

After the Rank transformation identifies all rows that belong to a top or bottom rank, it then assigns rank index values. In the case of the top 50 employees, measured by salary, the highest paid employee receives a rank index of 1. The next highest-paid employee receives a rank index of 2, and so on. When measuring a bottom rank, such as the 10 lowest priced products in the inventory, the Rank transformation assigns a rank index from lowest to highest. Therefore, the least expensive item would receive a rank index of 1.

If two rank values match, they receive the same value in the rank index and the transformation skips the next value. For example, if you want to see the top five retail stores in the country and two stores have the same sales, the return data might look similar to the following:

RANKINDEX SALES STORE

1 10000 Orange

1 10000 Brea

3 90000 Los Angeles

4 80000 Ventura

Creating a Rank Transformation

You can add a Rank transformation anywhere in the mapping after the source qualifier.

To create a Rank transformation:

1.

In the Mapping Designer, click Transformation > Create. Select the Rank transformation. Enter a name for the Rank. The naming convention for Rank transformations is RNK_TransformationName.

Enter a description for the transformation. This description appears in the Repository Manager.2. Click Create, and then click Done.The Designer creates the Rank transformation.

3. Link columns from an input transformation to the Rank transformation.4. Click the Ports tab and select the Rank (R) option for the rank port.If you want to create groups for ranked rows, select Group By for the port that defines the group.5. Click the Properties tab and select whether you want the top or bottom rank.

6. For the Number of Ranks option, enter the number of rows you want to select for the rank.

7. Change the other Rank transformation properties, if necessary.The following table describes the Rank transformation properties:

Setting DescriptionCache Directory Local directory where the Integration Service creates the index

and data cache files. By default, the Integration Service uses the directory entered in the Workflow Manager for the process variable $PMCacheDir. If you enter a new directory, make sure the directory exists and contains enough disk space for the cache files.

Top/Bottom Specifies whether you want the top or bottom ranking for a column.

Number of Ranks Number of rows you want to rank.Case-Sensitive String Comparison

When running in Unicode mode, the Integration Service ranks strings based on the sort order selected for the session. If the session sort order is case sensitive, select this option to enable case-sensitive string comparisons, and clear this option to have the Integration Service ignore case for strings. If the sort order is not case sensitive, the Integration Service ignores this setting. By default, this option is selected.

Tracing Level Determines the amount of information the Integration Service writes to the session log about data passing through this transformation in a session.

Rank Data Cache Size

Data cache size for the transformation. Default is 2,000,000 bytes. If the total configured session cache size is 2 GB (2,147,483,648 bytes) or more, you must run the session on a 64-bit Integration Service. You can configure a numeric value, or you can configure the Integration Service to determine the cache size at runtime. If you configure the Integration Service to determine the cache size, you can also configure a maximum amount of memory for the Integration Service to allocate to the cache.

Rank Index Cache Size

Index cache size for the transformation. Default is 1,000,000 bytes. If the total configured session cache size is 2 GB (2,147,483,648 bytes) or more, you must run the session on a 64-bit Integration Service. You can configure a numeric value, or you can configure the Integration Service to determine the cache size at runtime. If you configure the Integration Service to determine the cache size, you can also configure a maximum amount of memory for the Integration Service to allocate to the cache.

Transformation Scope

Specifies how the Integration Service applies the transformation logic to incoming data:

-

Transaction. Applies the transformation logic to all rows in a transaction. Choose Transaction when a row of data depends on all rows in the same transaction, but does not depend on rows in other transactions.

-

All Input. Applies the transformation logic on all incoming data. When you choose All Input, the PowerCenter drops incoming transaction boundaries. Choose All Input when a row of data depends on all rows in the source.

8. Click OK.