What is integer overflow in R and how can it happen?

Question

I have some calculation going on and get the following warning (i.e. not an error):

Warning messages:
1: In sum(myvar, na.rm = T) :
Integer overflow - use s         


        

Answer 1

In short, integer is an exact type with limited range, and numeric is a floating-point type that can represent a much wider range of value but is inexact. See the help pages (?integer and ?numeric) for further details.

As to the overflow, here is an explanation by Brian D. Ripley:

It means that you are taking the mean [in your case, the sum -- @aix] of some very large integers, and the calculation is overflowing. It is just a warning.

This will not happen in the next release of R.

You can specify that a number is an integer by giving it the suffix L, for example, 1L is the integer one, as opposed to 1 which is a floating point one, with class "numeric".

The largest integer that you can create on your machine is given by .Machine$integer.max.

> .Machine$integer.max
[1] 2147483647
> class(.Machine$integer.max)
[1] "integer"

Adding a positive integer to this causes an overflow, returning NA.

> .Machine$integer.max + 1L
[1] NA
Warning message:
In .Machine$integer.max + 1L : NAs produced by integer overflow
> class(.Machine$integer.max + 1L)
[1] "integer"

You can get round this limit by adding floating point values instead.

> .Machine$integer.max + 1
[1] 2147483648
> class(.Machine$integer.max + 1)
[1] "numeric"

Since in your case the warning is issued by sum, this indicates that the overflow happens when the numbers are added together. The suggested workaround sum(as.numeric(.)) should do the trick.