The argument values supplied to a PL/R function's script are the input arguments converted to a corresponding R form. See Table 4-1. Scalar PostgreSQL values become single element R vectors. One exception to this are scalar bytea values. These are first converted to R raw type, and then processed by the R unserialize command. One-dimensional PostgreSQL arrays are converted to multi-element R vectors, two-dimensional PostgreSQL arrays are mapped to R matrixes, and three-dimensional PostgreSQL arrays are converted to three-dimensional R arrays. Greater than three-dimensional arrays are not supported. Composite-types are transformed into R data.frames.
Table 4-1. Function Arguments
| PostgreSQL type | R type |
|---|---|
| boolean | logical |
| int2, int4 | integer |
| int8, float4, float8, cash, numeric | numeric |
| bytea | object |
| everything else | character |
Conversely, the return values are first coerced to R character, and therefore anything that resolves to a string that is acceptable input format for the function's declared return type will produce a result. Again, there is an exception for scalar bytea return values. In this case, the R object being returned is first processed by the R serialize command, and then the binary result is directly mapped into a PostgreSQL bytea datum. Similar to argument conversion, there is also a mapping between the dimensionality of the declared PostgreSQL return type and the type of R object. That mapping is shown in Table 4-2
Table 4-2. Function Result Dimensionality
| PgSQL return type | R type | Result | Example |
|---|---|---|---|
| scalar | array, matrix, vector | first column of first row | c(1,2,3) in R returns 1 in PostgreSQL |
| setof scalar | 1D array, greater than 2D array, vector | multi-row, 1 column set | array(1:10) in R returns 10 rows in PostgreSQL |
| scalar | data.frame | textual representation of the first column's vector | data.frame(c(1,2,3)) in R returns 'c(1, 2, 3)' |
| setof scalar | 2D array, matrix, data.frame | #columns > 1, error; #columns == 1, multi-row, 1 column set | (as.data.frame(array(1:10,c(2,5))))[,1] in R returns 2 rows of scalar |
| array | 1D array, greater than 3D array, vector | 1D array | array(1:8,c(2,2,2,2)) in R returns {1,2,3,4,5,6,7,8,1,2,3,4,5,6,7,8} |
| array | 2D array, matrix, data.frame | 2D array | array(1:4,c(2,2)) in R returns {{1,3},{2,4}} |
| array | 3D array | 3D array | array(1:8,c(2,2,2)) in R returns {{{1,5},{3,7}},{{2,6},{4,8}}} |
| composite | 1D array, greater than 2D array, vector | first row, 1 column | array(1:8,c(2,2,2)) in R returns 1 row of scalar |
| setof composite | 1D array, greater than 2D array, vector | multi-row, 1 column set | array(1:8,c(2,2,2)) in R returns 8 rows of scalar |
| composite | 2D array, matrix, data.frame | first row, multi-column | array(1:4,c(2,2)) in R returns 1 row of 2 columns |
| setof composite | 2D array, matrix, data.frame | multi-row, multi-column set | array(1:4,c(2,2)) in R returns 2 rows of 2 columns |