R language scalar function 1

The following example creates a function that returns the total length of all character input columns.

Code

In R AE, the main object that is provided by the user is a function that is referred to as nz.fun. It encapsulates the main AE loop and uses the R AE API to receive and output data. The following example shows the applyop implementation in R.

Enter the following code in the /tmp/applyop.R file:

nz.fun <- function () {
while(getNext()) {
op <- getInputColumn(0)
X <- c()
for (i in seq(1, inputColumnCount()-1)) {
x <- as.numeric(getInputColumn(i))
if (!is.null(x) && !is.na(x))
X <- append(X, x)
}
if (op != '+' && op != '*')
stop('incorrect operator: ', op)
setOutputInt32(0, eval(parse(text=paste(X, collapse=op))))
outputResult()
}
}

The main loop ends when getNext() returns false, which indicates that there are no more input rows to process. Each input row is accessed by the getInputColumn() that returns the value of the column that is specified by its index. The index of the first column is zero, and the index of the last column is inputColumnCount()-1. The output values are handled by the setOutput* functions, where the asterisk represents a specific data type identifier. To send the output values to the database, the outputResult() function must be called.

If an error occurs, call the standard R stop() function, or use the AE API function named userError(). Both functions interrupt program execution and return the error message to the caller.

Compilation

Compile the code as follows:

/nz/export/ae/utilities/bin/compile_ae --language r \
--version 3 --template compile --user nz --db dev \
/tmp/applyop.R

During the compilation step, the input source file is serialized by using standard R API and prepared for further execution. The output is stored under a predefined path that is accessible from the Host and on the SPUs, depending on the database and user names.

Registration

After the compilation is completed, you must register the code. For the registration step, the following conditions apply:

As the template name, udf must be specified.
User name, database name, and UDX signature including output type must match the compilation values.
The executable name must match the source file name from the compilation step.

/nz/export/ae/utilities/bin/register_ae --language r \
--version 3 --user nz --db dev --template udf \
--sig 'applyop(VARARGS)' --return INT4 --exe applyop.R

Running

When you run the registered UDAP, you get the following result:

SELECT applyop('+', 4, 10);
APPLYOP
---------
14
(1 row)
SELECT applyop('*', 3, 5);
APPLYOP
---------
15
(1 row)

The following example shows error handling:

SELECT applyop('-', 3, 5);
ERROR: Error in function () : incorrect operator: -