Why is NA^0 in R gives 1 and not NA

Question

I've just encounter a weird behaviour of R which I would like to understand.

When I do NA^0 it gives 1 and not NA as I would have expected.

example:

v1 <- c(2,NA,1)
v1^0
[1] 1 1 1
v1**0
[1] 1 1 1

^ and ** are arithmetic operators (help("^")) like -, +, etc. which in their case gives NA:

v1+0
[1]  2 NA  1
v1-0
[1]  2 NA  1

Why are the different operators performe differently with NAs?

I remember my mathematics teacher saying ***"Anything raise to 0 is 1".*** — Ronak Shah, Mar 13 '17 at 12:39
This is what it does. This result has been exploited on a number of SO answers to produce vectorized solutions in the presence of NA values. — lmo, Mar 13 '17 at 12:40
You can look at this: http://stackoverflow.com/questions/17863619/why-does-nan0-1 — PKumar, Mar 13 '17 at 12:41
@Ronak Shah Even a NULL value??? I know the mathematical law for numbers, but from a computer point of view, I would have expected (and prefer) that NULL value stay NULL when raised to 0... — Bastien, Mar 13 '17 at 12:42
NA is *not* equivalent to NULL. From the help file `?NA`: "NA is a logical constant of length 1 which contains a missing value indicator." and from `?NULL`, "NULL represents the null object in R." These are distinct concepts. Consider a data.frame, df, with variable v1. `df$v1 <- NA` sets the values of the variable to missing, whereas `df$v1 <- NULL` removes the variable. — lmo, Mar 13 '17 at 12:45
After a quick read of the like posted (which I missed in my search, I apologise), I see the point of that behaviour. Personnaly, I would have prefer the other behaviour to be able to use this operation as a `is.na` alternative. Anyway, thanks for the explanations. — Bastien, Mar 13 '17 at 12:50

score 0 · Answer 1 · edited May 23 '17 at 12:17

0

I voted to close this as a duplicate, but since your question seems to be "how can I avoid this behavior and return NA instead":

your_exp <- Vectorize(function(base, exp) ifelse(is.na(base),NA,base^exp))
v1 <- c(2,NA,1)

your_exp(v1,0)
# returns [1]  1 NA  1

Please see the accepted answer for why NA^0 == 1.

edited May 23 '17 at 12:17

Community

answered Mar 13 '17 at 12:47

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1 Answers1