python - 如何在rpy2中使用R的赋值方法？

Question

我正在使用 rpy2，我需要对 R 对象使用赋值方法。例如，从这个对象开始:

# Python code
from rpy2.robjects import r
myvar = r('c(a=1,b=2,c=3)')

假设我想分配给names(myvar) . (注意:请忽略 rpy2 提供了另一种通过 myvar.names 访问名称的方法。这仅适用于名称，不适用于任意分配方法。)在 R 中，我会这样做:

# R code
names(myvar) <- c("x", "y", "z")

但是，这在 Python 中不起作用:

# Python code
> names(myvar) = ['x', 'y', 'z']
In [62]: names(myvar) = ['x', 'y', 'z']
  File "<ipython-input-62-aa3f7998cdcb>", line 1
    names(myvar) = ['x', 'y', 'z']
                                  ^
SyntaxError: can't assign to function call

当然，我可以通过 rpy2 的字符串 eval 运行任意代码:

# Python code
r('''names(myvar) <- c("x", "y", "z")''')

但是将值插入要评估的字符串中听起来既不有趣也不安全。那么有没有办法安全地做相当于 method(object) <- value 的事情呢？通过 rpy2？

Answer 1

在 R 中，“setter”函数遵循命名约定，即“getter”的名称后跟 <-。 .例如，当做

names(myvar) <- c("x", "y", "z")

发生以下情况:

myvar <- "names<-"(myvar, c("x","y","z"))

如果我们分解它:

> myvar = c(a=1,b=2,c=3)
> # call the assignment function "names<-"    
> "names<-"(myvar, c("x","y","z")) 
x y z 
1 2 3 
> # the "names" are stored as an attribute
> attributes(myvar)
$names
[1] "x" "y" "z"
> attributes(myvar)$names <- c("a","b","c")
> myvar
a b c 
1 2 3 
> # note that the function does have a side effect
> # (unlike what I wrote in a previous version of this answer):
> # the names are changed in place. I think that this is a C-level
> # optimization specific to "names" and this may not always be
> # the case for all "setters"
> "names<-"(myvar, c("x","y","z")) 
x y z 
1 2 3 
> myvar
x y z 
1 2 3   

做类似 method(object) <- value 的事情来自 rpy2 很简单。 python 代码看起来像:

set_method = r("`method<-`")
my_object = set_method(my_object, value)