r - 从字符串中计算 NA_integer_

Question

如何(从文件中)读取“NA_integer”之类的值，并让 R 将其解释为显式键入 NA_integer 。

这是我失败的两次尝试:

q <- "NA_integer_"
get(q)        # Returns "Error in get(q) : object 'NA_integer_' not found"
eval(q)       # Returns the character value

这是我能得到的最接近的结果。但我不喜欢它，因为它牺牲了很多普遍性。

f <- "as.integer"
v <- NA
do.call(f, list(v))

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Answer 1

根据？NA

NA is a logical constant of length 1 which contains a missing value indicator. NA can be coerced to any other vector type except raw. There are also constants NA_integer_, NA_real_, NA_complex_ and NA_character_ of the other atomic vector types which support missing values: all of these are reserved words in the R language.

所以我们需要

q <- "NA_integer_"

然后使用

eval(parse(text=q))
#[1] NA