Tag Archives: NA

The difference between “letters[c(1,NA)]” and “letters[c(NA,NA)]“

In David Smith’s latest blog post (which, in a sense, is a continued response to the latest public attack on R), there was a comment by Barry that caught my eye. Barry wrote:

Even I get caught out on R quirks after 20 years of using it. Compare letters[c(12,NA)] and letters[c(NA,NA)] for the most recent thing that made me bang my head against the wall.

So I did, and here’s the output:

> letters[c(12,NA)]
[1] "l" NA 
>  letters[c(NA,NA)] 
 [1] NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
>

Interesting isn’t it?
I had no clue why this had happened but luckily for us, Barry gave a follow-up reply with an explanation. And here is what he wrote:
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