@符号在R中是什么意思？

Question

In packages like marray and limma , when complex objects are loaded, they contain "members variables" that are accessed using the @ symbol. What does this mean and how does it differ from the $ symbol?

Answer 1

See ?'@' :

• Description:

  Extract the contents of a slot in a object with a formal (S4) class structure.

• Usage:

  object@name

  ...

---

The S language has two object systems, known informally as S3 and S4.

• S3 objects, classes and methods have been available in R from the beginning, they are informal, yet very interactive . S3 was first described in the White Book (Statistical Models in S).
• S3 is not a real class system, it mostly is a set of naming conventions.
• S4 objects, classes and methods are much more formal and rigorous, hence less interactive . S4 was first described in the Green Book (Programming with Data). In R it is available through the methods package, attached by default since version 1.7.0.

See also this document: S4 Classes and Methods .

Answer 2

正如其他人所说的，@符号用于S4类，但这是Google R风格指南的注释：“除非有充分的理由使用S4对象或方法，否则请使用S3对象和方法。”

Answer 3

您将需要阅读使用@符号的S4类。