RNull
更多信息和选项
- RNull corresponds to Mathematica's Null.
- Unless you manually construct or otherwise work with the RLink internal form of expressions representing R objects, you are unlikely to be using this head.
范例
基本范例 (1)
Mathematica's Null is interpreted as R NULL during conversion to RLink's internal representation:
Of course, it also works in another direction:
You can set a variable (or part of an expression, e.g. part of a list) to NULL:
Comparison to NULL does not really work—it returns a logical vector of length 0:
You can, however, test the type of the value stored in the test variable:
The proper way to test for NULL is via the is.null built-in R function:
Vectors of zero length are also considered NULL in R:
For this reason, assigning NULL to a vector's element is an error:
Assigning NULL to an element of a list is not an error, and effectively deletes that element from a list. Here is a test list:
This will assign NULL to its second element:
This is equivalent to removal of that element from a list:
In some sense, R NULL therefore combines the behavior of Mathematica's Null and Mathematica's Sequence[].
文本
Wolfram Research (2012),RNull,Wolfram 语言函数,https://reference.wolfram.com/language/RLink/ref/RNull.html.
CMS
Wolfram 语言. 2012. "RNull." Wolfram 语言与系统参考资料中心. Wolfram Research. https://reference.wolfram.com/language/RLink/ref/RNull.html.
APA
Wolfram 语言. (2012). RNull. Wolfram 语言与系统参考资料中心. 追溯自 https://reference.wolfram.com/language/RLink/ref/RNull.html 年