R: is.na() 不获取 NA 值

Question

所以我有一个数据集，只需查看它，数据集中就有明显的 NA。

 > dput(bmi.cig)
structure(list(MSI.subset.BMI = structure(c(4L, 4L, 4L, 4L, 4L, 
4L, 4L, 4L, 4L, 4L, 4L, 1L, 2L, 3L, 3L, 1L, 3L, 3L, 1L, 4L, 4L, 
4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L), .Label = c("0", "1", "2", 
"NA"), class = "factor"), MSI.subset.Cigarette = structure(c(3L, 
3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 2L, 2L, 1L, 2L, 1L, 2L, 
2L, 2L, 2L, 1L, 2L, 1L, 2L, 2L, 2L, 1L, 1L, 1L, 1L), .Label = c("1", 
"2", "NA"), class = "factor")), .Names = c("MSI.subset.BMI", 
"MSI.subset.Cigarette"), row.names = c(NA, 30L), class = "data.frame")


> head(bmi.cig)
  MSI.subset.BMI MSI.subset.Cigarette
1             NA                   NA
2             NA                   NA
3             NA                   NA
4             NA                   NA
5             NA                   NA
6             NA                   NA

我想删除任何列中包含 NA 的行，因此我使用了 ForImp 包中的列表删除函数 ld。但是，R 不识别 NA 值。

is.na(bmi.cig$MSI.subset.BMI)

我明白了

    > is.na(bmi.cig$MSI.subset.BMI)
 [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
[26] FALSE FALSE FALSE FALSE FALSE

因此，一旦我使用 ld 函数，我只会得到一个空数据集作为返回。

Answer 1

b/c 列是因子，级别是 “NA”。即，尝试

data <- structure(list(MSI.subset.BMI = structure(c(4L, 4L, 4L, 4L, 4L, 
+ 4L, 4L, 4L, 4L, 4L, 4L, 1L, 2L, 3L, 3L, 1L, 3L, 3L, 1L, 4L, 4L, 
+ 4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L), .Label = c("0", "1", "2", 
+ "NA"), class = "factor"), MSI.subset.Cigarette = structure(c(3L, 
+ 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 2L, 2L, 1L, 2L, 1L, 2L, 
+ 2L, 2L, 2L, 1L, 2L, 1L, 2L, 2L, 2L, 1L, 1L, 1L, 1L), .Label = c("1", 
+ "2", "NA"), class = "factor")), .Names = c("MSI.subset.BMI", 
+ "MSI.subset.Cigarette"), row.names = c(NA, 30L), class = "data.frame")
> class(blah[,1])

data[,1]=="NA"

NA 实际上是字符 (class("NA"))，而不是像 class(NA) 这样的 logical 类)。