Internal representation of int NA

Question

This is question about R internals. How integer NA values are represented in R? Unlike floating there is no magic bit sequence to represent NaNs.

# Create big array. newer versions of R won't allocate memory to store data
# Instead star/end values are stored internally
a <- 1:1e6 # 

# Change some random value. This will cause and array to be allocated
a[123] <- NA
typeof(a)

At this point a is still an array of integers. How a[123] represented internally? Does R use some magic number to indicate that an integer is NA?

My primary interest in internal representation of integers is related to binary read/write (readBin/writeBin). How to handle NA when performing binary I/O with external sources, e.g. via sockets?

Maybe this will give you an answer : https://stackoverflow.com/questions/51684861/how-does-r-represent-na-internally — Rémi Coulaud, Jun 08 '19 at 15:44

score 4 · Accepted Answer · answered Jun 08 '19 at 15:44

4

R uses the minimum integer value to represent NA. On a 4-byte system, valid integer values are usually -2,147,483,648 to 2,147,483,647 but in R

> .Machine$integer.max
[1] 2147483647
> -.Machine$integer.max
[1] -2147483647
> -.Machine$integer.max - 1L
[1] NA
Warning message:
In -.Machine$integer.max - 1L : NAs produced by integer overflow

Also,

> .Internal(inspect(NA_integer_))
@7fe69bbb79c0 13 INTSXP g0c1 [NAM(7)] (len=1, tl=0) -2147483648

answered Jun 08 '19 at 15:44

Martin Morgan

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I have updated my question, but I think the answer is evident from your post – quantum_well Jun 08 '19 at 15:50
1

`.Machine$integer.max + 1L` is outside the 'usual' range, so is replaced by the NA value. – Martin Morgan Jun 08 '19 at 17:13

Internal representation of int NA

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