About the ore.frame Class

1.4.2.2 About the ore.frame Class

An ore.frame object represents a relational query for an Oracle Database instance.

It is the OML4R equivalent of a data.frame. Typically, you get ore.frame objects that are proxies for database tables. You can then add new columns, or make other changes, to the ore.frame proxy object. Any such change does not affect the underlying table. If you then request data from the source table of the ore.frame object, the transparency layer function generates a SQL query that has the additional columns in the select list, but the table is not changed.

In R, the elements of a data.frame have an explicit order. You can specify elements by using integer indexing. In contrast, relational database tables do not define any order of rows and therefore cannot be directly mapped to R data structures.

OML4R has both ordered and unordered ore.frame objects. If a table has a primary key, which is a set of one or more columns that form a distinct tuple within a row, you can produce ordered results by performing a sort using an ORDER BY clause in a SELECT statement. However, ordering relational data can be expensive and is often unnecessary for transparency layer operations. For example, ordering is not required to compute summary statistics when invoking the summary function on an ore.frame.

See Also:

"Moving Data to and from the Database" for information on ore.create

"Creating Ordered and Unordered ore.frame Objects".

Example 1-4 Classes of a data.frame and a Corresponding ore.frame

This example creates a data.frame with columns that contain different data types and displays the structure of the data.frame. The example then invokes the ore.push function to create a temporary table in the database that contains a copy of the data of the data.frame. The ore.push invocation also generates an ore.frame object that is a proxy for the table. The example displays the classes of the ore.frame object and of the columns in the data.frame and the ore.frame objects.

df <- data.frame(a="abc",
                 b=1.456,
                 c=TRUE,
                 d=as.integer(1),
                 e=Sys.Date(),
                 f=as.difftime(c("0:3:20", "11:23:15")))
ore.push(df)
class(of)
class(df$a
class(of$a)
class(df$b)
class(of$b)
class(df$c)
class(of$c)
class(df$d)
class(of$d)
class(df$e)
class(of$e)
class(df$f)
class(of$f)

Listing for Example 1-4

R> df <- data.frame(a="abc",
+                   b=1.456,
+                   c=TRUE,
+                   d=as.integer(1),
+                   e=Sys.Date(),
+                   f=as.difftime(c("0:3:20", "11:23:15")))
R> ore.push(df)
R> class(of)
[1] "ore.frame"
attr(,"package")
[1] "OREbase"
R> class(df$a)
[1] "factor"
R> class(of$a)
[1] "ore.factor"
attr(,"package")
[1] "OREbase"
R> class(df$b)
[1] "numeric"
R> class(of$b)
[1] "ore.numeric"
attr(,"package")
[1] "OREbase"
R> class(df$c)
[1] "logical"
R> class(of$c)
[1] "ore.logical"
attr(,"package")
[1] "OREbase"
R> class(df$d)
[1] "integer"
R> class(of$d)
[1] "ore.integer"
attr(,"package")
[1] "OREbase"
R> class(df$e)
[1] "Date"
R> class(of$e)
[1] "ore.date"
attr(,"package")
[1] "OREbase"
R> class(df$f)
[1] "difftime"
R> class(of$f)
[1] "ore.difftime"
attr(,"package")
[1] "OREbase"

Parent topic: Transparency Layer Support for R Data Types and Classes