函数名称用R中的单引号引起来 [英] Function name in single quotation marks in R

问题描述

这可能是一个愚蠢的问题，但我一直困扰了很长一段时间。我已经看到人们在定义函数时使用单引号来围绕函数名称。我一直想知道这样做的好处。下面是一个简单的例子

 'row.mean'<  -  function（mat）{
 return（apply（ mat，1，mean））
} 
  

预先感谢！

解决方案

在理查德的假设下，后面的勾号允许您使用通常不被允许的名称中的符号。请参阅：

 `add + 5`<  -  function（x）{return（x + 5）} 
  

定义了一个函数，但是

  add + 5 < -  function（x）{return（x + 5）} 
  

返回

  add + 5错误< -  function（x）{：object'add'not found 
  

要引用该函数，您还需要明确使用back tick。

 > `add + 5`（3）
 [1] 8 
  

查看代码这个函数只需调用它就可以不带参数：

 > `add + 5` 
 function（x）{return（x + 5）} 
  

另请参阅此评论，它涉及名称分配中反引号与引号之间的区别： https://stat.ethz.ch/pipermail/r-help/2006-December/121608.html

注意，用法的后蜱更普遍。例如，在一个数据框中，你可以有用整数命名的列（也许从整数因子使用 reshape :: cast ）。

例如：

  test = data.frame（a =a，b =b） 
名称（test）<  -  c（1,2）
  

并检索这些列可以使用反向符号与 $ 运算符一起使用，例如：

 >测试$ 1 
错误：test $ 1中出现意外的数字常量
  

但

 >测试$`1` 
 [1] a 
等级：a 
  

Funnily您不能在分配数据框列名称时使用返回勾号;以下不起作用：

  test = data.frame（`1` =a，`2` = b）
  

响应statechular的评论，这里有两个用例。

在修复函数中使用％


c>符号我们可以天真地定义向量 x 和 y 之间的点积：



 `％。％`<  -  function（x，y）{
 
 sum（x * y）
 
 
  

给出


 > c（1,2）％。％c（1,2）
 [1] 5 
  



<请参阅： http：// dennisphdblog。 wordpress.com/2010/09/16/infix-functions-in-r/

替换功能

下面是一个很好的答案，它展示了这些内容：什么是R中的替换函数？

It may be a silly question but I have been bothered for quite a while. I've seen people use single quotation marks to surround the function name when they are defining a function. I keep wondering the benefit of doing so. Below is a naive example

'row.mean' <- function(mat){
    return(apply(mat, 1, mean))
}

Thanks in advance!

解决方案

Going off Richard's assumption, the back ticks allows you to use symbols in names which are normally not allowed. See:

`add+5` <- function(x) {return(x+5)}

defines a function, but

add+5 <-  function(x) {return(x+5)}

returns

Error in add + 5 <- function(x) { : object 'add' not found

To refer to the function, you need to explicitly use the back ticks as well.

> `add+5`(3)
[1] 8

To see the code for this function, simply call it without its arguments:

> `add+5`
function(x) {return(x+5)}

See also this comment which deals with the difference between the backtick and quotes in name assignment: https://stat.ethz.ch/pipermail/r-help/2006-December/121608.html

Note, the usage of back ticks is much more general. For example, in a data frame you can have columns named with integers (maybe from using reshape::cast on integer factors).

For example:

test = data.frame(a = "a", b = "b")
names(test) <- c(1,2)

and to retrieve these columns you can use the backtick in conjunction with the $ operator, e.g.:

> test$1
Error: unexpected numeric constant in "test$1"

but

> test$`1`
[1] a
Levels: a

Funnily you can't use back ticks in assigning the data frame column names; the following doesn't work:

test = data.frame(`1` = "a", `2` = "b")

And responding to statechular's comments, here are the two more use cases.

In fix functions

Using the % symbol we can naively define the dot product between vectors x and y:

`%.%` <- function(x,y){

    sum(x * y)

}

which gives

> c(1,2) %.% c(1,2)
[1] 5

for more, see: http://dennisphdblog.wordpress.com/2010/09/16/infix-functions-in-r/

Replacement functions

Here is a great answer demonstrating what these are: What are Replacement Functions in R?

这篇关于函数名称用R中的单引号引起来的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！