The variable .Classis set to the class attribute of x, .Generic is set to the string “mean” and a search is made for the correct method to invoke. The class attributes of any other arguments to mean are ignored. If they are then there will be no.Generic, .Class or .Method. In this case thegeneric argument of NextMethod must be specified.
However the object, i.e. the first argument has been evaluated. function is being evaluated the actual expression used as an argument is stored in the promise together with a pointer to the environment the function was called from.
Execution will halt on the next statement that is evaluated in R. A symbolic debugger such asgdb can be used to debug compiled code.
object-oriented system R has a class system and a mechanism for dispatching based on the class of an object. The dispatch mechanism for interpreted code relies on four special objects that are stored in the evaluation frame.
The result is the concatenation of the list of formal arguments with the function body. Conversely such a list can be converted to a function using as.function. This functionality is mainly included for S compatibility. Notice that environment information is lost when as.list is used, whereasas.function has an argument that allows the environment to be set. When the group is Ops the special variable .Method is a string vector with two elements.
In the case of $, the index argument is of mode”symbol” even when using the x$”abc” form. It is important to be aware that class methods do not necessarily behave in the same way as the basic methods, for example with respect to partial matching. The difference between the two lies in the argument handling. When a function is called, a new environment (called theevaluation environment) is created, whose enclosure (seeEnvironment objects) is the environment from the function closure. This new environment is initially populated with the unevaluated arguments to the function; as evaluation proceeds, local variables are created within it.
The debugger provides access only to interpreted expressions. If a function calls a foreign language (such as C) then no access to the statements in that language is provided.
There is no way to change the other arguments in the call to the method; these remain as they were in the call to the generic. This is in contrast to NextMethod where the arguments in the call to the next method can be altered. When the method is invoked it is called with arguments that are the same in number and have the same names as in the call to the generic. They are matched to the arguments of the method according to the standard R rules for argument matching.
The purpose of this manual is to document the language per se. That is, the objects that it works on, and the details of the expression evaluation process, which are useful to know when programming R functions. Major subsystems for specific tasks, such as graphics, are only briefly described in this manual and will be documented separately. Internally, a function definition is stored as a function call with function name function and two arguments, the arglist and the body. The arglist is stored as a tagged pairlist where the tags are the argument names and the values are the default expressions.
It is evaluated so that the required method can be determined. In this case the first argument in the call to the generic is not evaluated and is discarded.
R has an elaborate class system1, principally controlled via the class attribute. This attribute is a character vector containing the list of classes that an object inherits from. This forms the basis of the “generic methods” functionality in R. Environments are created implicitly by function calls, as described inFunction objects and Lexical environment. In this case the environment contains the variables local to the function (including the arguments), and its enclosure is the environment of the currently called function.
They can be used anywhere that an R object is required. In particular they can be passed as arguments to functions and returned as values from functions.
When (if) the argument is evaluated the stored expression is evaluated in the environment that the function was called from. Since only a pointer to the environment is used any changes made to that environment will be in effect during this evaluation. The resulting value is then also stored in a separate spot in the promise.
2 Functions as objects
- The dispatch mechanism for interpreted code relies on four special objects that are stored in the evaluation frame.
- These special objects are .Generic, .Class, .Method and.Group.
- object-oriented system R has a class system and a mechanism for dispatching based on the class of an object.
After the initial call to UseMethod these special variables, not the object itself, control the selection of subsequent methods. The operator [ is a generic function which allows class methods to be added, and the $ and [[ operators likewise. Thus, it is possible to have user-defined indexing operations for any structure. Such a function, say [.foo is called with a set of arguments of which the first is the structure being indexed and the rest are the indices.
What r means?
R is a system for statistical computation and graphics. It provides, among other things, a programming language, high level graphics, interfaces to other languages and debugging facilities. This manual details and defines the R language.
The value of .Class is taken to be the class attribute of the object which is the first argument to the current function. The value of.Method is the name of the current function. These choices for default values ensure that the behaviour of a method doesn’t change depending on whether it is called directly or via a call to a generic. If the first argument to UseMethod is not supplied it is assumed to be the name of the current function. If two arguments are supplied to UseMethod then the first is the name of the method and the second is assumed to be the object that will be dispatched on.
In R, generic functions are used to determine the appropriate method. The generic function is responsible for determining the class of its argument(s) and uses that information to select the appropriate method. The call to UseMethod has the effect of placing some special objects in the evaluation frame. These special objects are used to by R to handle the method dispatch and inheritance.
If substitute is invoked inside a function, the local variables of the function are also subject to substitution. generic functions is to provide print andsummary methods for statistical objects, generally the output of some model fitting process. To do this, each model attaches a class attribute to its output and then provides a special method that takes that output and provides a nice readable version of it. The user then needs only remember that print or summary will provide nice output for the results of any analysis. When mean is called it can have any number of arguments but its first argument is special and the class of that first argument is used to determine which method should be called.
.Class is the class of the object, .Generic is the name of the generic function and .Method is the name of the method currently being invoked. If the method was invoked through one of the internal interfaces then there may also be an object called .Group.
The elements of .Method are set to the name of the method if the corresponding argument is a member of the class that was used to determine the method. Otherwise the corresponding element of .Method is set to the zero length string, “”.
parse tree for the first is matched against the second argument, which can be a tagged list or an environment frame. If it is a simple local object, its value is inserted, except if matching against the global environment. If it is a promise (usually a function argument), the promise expression is substituted.
Subsequent evaluations retrieve this stored value (a second evaluation is not carried out). Access to the unevaluated expression is also available using substitute.
What does R mean in a text message?
The “R” inside the circle stands for “registered.” The “R” and circle together form the federal trademark registration symbol. In commerce, the symbol shows that your business officially owns its trademark by U.S. Patent and Trade Office (pto.gov) standards.
These special objects are .Generic, .Class, .Method and.Group. There is a separate dispatch mechanism used for internal functions and types that will be discussed elsewhere. functions that are specialized to carry out specific calculations on objects, usually of a specific class.
Evaluation of expressions
The special exception for substituting at the top level is admittedly peculiar. substitutewill recognize a promise variable and substitute the value of its expression slot.