需要的示例：更改对象的默认打印方法

Question

我需要一些专业术语以及一小段示例代码。不同类型的对象具有输入对象名称的特定方式，并按下Enter键，lm对象显示模型摘要，矢量列出矢量内容。

我希望能够写出自己的方式来“显示”特定类型对象的内容。理想情况下，我希望能够从现有类型的对象中分离出来。

我该怎么做呢？

Answer 1

下面是一个让你开始的例子。一旦您了解了如何分派S3方法的基本概念，请查看methods("print")返回的任何打印方法，以了解如何获得更有趣的打印样式。

## Define a print method that will be automatically dispatched when print() 
## is called on an object of class "myMatrix" 
print.myMatrix <- function(x) { 
    n <- nrow(x) 
    for(i in seq_len(n)) { 
     cat(paste("This is row", i, "\t: ")) 
     cat(x[i,], "\n") 
     } 
} 

## Make a couple of example matrices 
m <- mm <- matrix(1:16, ncol=4) 

## Create an object of class "myMatrix". 
class(m) <- c("myMatrix", class(m)) 
## When typed at the command-line, the 'print' part of the read-eval-print loop 
## will look at the object's class, and say "hey, I've got a method for you!" 
m 
# This is row 1 : 1 5 9 13 
# This is row 2 : 2 6 10 14 
# This is row 3 : 3 7 11 15 
# This is row 4 : 4 8 12 16 

## Alternatively, you can specify the print method yourself. 
print.myMatrix(mm) 
# This is row 1 : 1 5 9 13 
# This is row 2 : 2 6 10 14 
# This is row 3 : 3 7 11 15 
# This is row 4 : 4 8 12 16