R FNC Functions | R Table Operators | Teradata Vantage - R FNC Functions - Advanced SQL Engine - Teradata Database

An R table operator typically accesses and modifies data stored in the database to perform an assigned task.

The following sections describe FNC functions available to R table operator developers. These functions provide an interface for R scripts to access and update data and metadata from the database.

The following categories of functions are provided.

Functions for Data Manipulation

For table operators, the rows in the input and output streams are accessed following an iterator model such as the following:

1. Open the input and output streams.
2. Sequentially read the rows in the input stream.
3. Directly access the columns in the current input row.
4. Update the columns in the current output row.
5. Sequentially write the output rows.
6. Close the streams.

The following functions support the iterator model and are used to manipulate the input and output streams. These functions allow you to access and modify data in the database. Functions are also available to set and retrieve the format specification of input and output streams.

As with C protected mode table operators, a buffer is used for reading and writing rows. When a read row is issued, the system reads an entire buffer of rows so that the next time a read row is issued, it retrieves the row from the buffer. A new buffer is read when the end of the buffer is reached. Similarly, a buffer is used for writes. The size of the buffer is configurable and can be set in the cufconfig GDO(CServerMemSize).

Functions for Metadata Manipulation

For table operators, some metadata passed during query invocation can be accessed from the contract function and the operator. This metadata can be set in the contract function if it was not specified as part of the query. In addition, a contract function can set a context that can be accessed during execution of the operator.

The following functions are used to access and set this metadata and the contract context.

Functions to Access USING Clause Parameters

You can use USING clauses to pass parameters as key-value pairs to the contract function and table operator. The following functions are used to access these pairs in the contract function and table operator.

Functions for LOB Manipulation

The following functions are used to access and modify LOBs from R table operators. Using these functions, R table operators can read LOBs from input streams and create LOBs for output streams.

Functions For Setting Column Definitions

The following functions are used to generate lists for each of the supported data types. You can then pass these lists to the tdr.SetOutputColDef function. This allows you to define the lists in a quick and efficient manner so that you will not have to explicitly define each and every list used in calls to tdr.SetOutputColDef.

Some of the functions simply return the default attributes required for a specific data type. Other functions indicate certain properties about the data type, such as the length or character type, based on the parameters passed to the function.

Additional Functions for Developing R Table Operators

The following additional functions may also be useful when developing R table operators.

Prerequisite

Before calling these functions, the TDR package must be loaded by including the following statement in the R script.

library(tdr)

Terminology

R types do not include scalar types. Scalar types such as integers are typically represented as a unit vector of the given type (integer). In the following sections, unit vectors of a type are specified by giving only the type. For example, integer and character denote integer and character unit vectors, respectively. Vectors with more than one element are specified as type vector, for example, integer vector.