gmExpr
Creating gmExpressions
gmExpr
creates a gmExpression
- Keywords
- utilities
Usage
gmExpr(expr,...,envir=parent.frame(),EXPR=substitute(expr))
Arguments
- expr
- an R-like representation of an SQL query.
- envir
- defines the environment used for evaluation of
expr
. - EXPR
- The quoted version of such an expression.
- ...
- further arguments for later use in other methods.
Details
gmExpr
creates an object of class gmExpr
, which can be used as argument in gmRead
instead of a string. Furthermore it can be extended like any other expression used in gmRead
.
For use in the geometallurgical database you need to begin every expression with root
, since data storage starts from this common root object.
The composition of an expression is done in the following way: for accessing a certain object in a class, use the $
-operator, to access its elements use square brackets []
. By specifying columnName=operation
the user can control the content of a column in the the output. Named columns are always shown in the result. If they need to be dropped set them to operation drop
. If you want to group objects by a named column, set its operation to group
. This grouping can only be done for elements at least one step down in the hierarchy.
Value
-
An object of class
gmExpr
, containing the expression in $EXPR
and the envir
as attribute.
See Also
Examples
expr <- gmExpr(root$project)
## Not run:
# gmConnectServer(MySQL(), ...)
# gmRead(expr$series)
#
# gmRead(expr$series[name=gmTitle, name=drop])
# ## naming the element gmTitle as name and dropping it in the result
#
# gmRead(expr[pID=id]$series[name=gmTitle, pID=group])
# ## grouping the series by their corresponding project in the result
# ## End(Not run)