Source Code of R Method

There are different ways to view the source code of an R method or function. It will help to know how the function is working.

Internal Functions
If you want to see the source code of the internal function (functions from base packages), just type the name of the function at R prompt such as;

> rowMeans

Functions or Methods from S3 Class System
For S3 classes, methods function can be used to list the methods for a particular generic function or class.

> methods(predict)

Note that “Non-Visible functions are asterisked” means that the function is not exported from its package’s namespace.

One can still view its source code via the ::: function such as

> stats:::predict.lm

or by using getAnywhere() function, such as

> getAnywhere(predict.lm)

Note that the getAnywhere() function is useful as you don’t need to know from which package the function or method comes from.

Functions or Methods from S4 Class System
The S4 system is a newer method dispatch system and is an alternative to the S3 system. The package ‘Matrix’ is an example of S4 function.

> library(Matrix)
> chol2inv

The output already offers a lot of information. The standardGeneric is an indicator of an S4 function. The method to see defined S4 methods is to use showMethods(chol2inv), that is;

> showMethods(chol2inv)

The getMethod can be used to see the source code of one of the methods, such as,

> getMethod (“chol2inv”, “diagonalMatrix”)

Functions that Calls Unexported Functions
In the case of unexported functions such as ts.union, .cbindts and .makeNamesTs from the stats namespace, one can view source code of these unexported functions using ::: operator or getAnywhere() function, for example;

> stats::: .makeNamesTs
> getAnywhere(.makeNamesTs)

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