问题
I have the following vector:
x <- c(3, 7, NA, 4, 8)
And I just want to know the index of the NA in the vector. If, for instance, I wanted to know the index of 7, the following code would work:
> which(x == 7)
[1] 2
I find it odd that running the same code when trying to find the index of the NA does not give me the desired result.
> which(x == NA)
integer(0)
I also tried the following but it does not work:
> which(x == "NA")
integer(0)
Your help will be much appreciated.
Edit
The question has been answered below by @ccapizzano, but can anyone explain why the codes above do not work?
回答1:
You may want to try using the which and is.na functions in the the following manner:
which(is.na(x))
[1] 3
来源：https://stackoverflow.com/questions/23840193/finding-the-index-of-an-na-value-in-a-vector