r - if/while(condition){:参数长度为零时出错

Question

我收到了错误

Error in if (condition) { : argument is of length zero

要么

Error in while (condition) { : argument is of length zero

导致此错误消息的原因是什么？

经过进一步检查，似乎该值为 NULL。

condition
## NULL

为了处理此错误，如何测试NULL值？

我期望这将返回 TRUE，但是我得到了一个空的逻辑值:

condition == NULL
## logical(0)

Answer 1

参见?NULL
您必须使用is.null

‘is.null’ returns ‘TRUE’ if its argument is ‘NULL’ and ‘FALSE’ otherwise.

尝试这个:

if ( is.null(hic.data[[z]]) ) { print("is null")}

从 R Language Definition的2.1.6节开始

There is a special object called NULL. It is used whenever there is a need to indicate or specify that an object is absent. It should not be confused with a vector or list of zero length. The NULL object has no type and no modifiable properties. There is only one NULL object in R, to which all instances refer. To test for NULL use is.null. You cannot set attributes on NULL.