[R] large integers in R

[Duncan Murdoch]

On 28/01/2010 5:30 AM, Benilton Carvalho wrote:
> Hi Duncan,
> 
> On Tue, Jan 26, 2010 at 9:09 PM, Duncan Murdoch <murdoch at stats.uwo.ca> wrote:
>> On 26/01/2010 3:25 PM, Blanford, Glenn wrote:
>>> Has there been any update on R's handling large integers greater than 10^9
>>> (between 10^9 and 4x10^9) ?
>>>
>>> as.integer() in R 2.9.2 lists this as a restriction but doesnt list the
>>> actual limit or cause, nor if anyone was looking at fixing it.
>> Integers in R are 4 byte signed integers, so the upper limit is 2^31-1.
>>  That's not likely to change soon.
> 
> But in the hypothetical scenario that this was to change soon and we
> were to have 64bit integer type (say, when under a 64 bit OS),
> wouldn't this allow us to have objects whose length exceeded the
> 2^31-1 limit?

Those are certainly related problems, but you don't need 64 bit integers 
to have longer vectors.  We could switch to indexing by doubles in R 
(though internally the indexing would probably be done in 64 bit ints).

A problem with exposing 64 bit ints in R is that they break the rule 
that doubles can represent any integer exactly.  If x is an integer, x+1 
is a double, and it would be unfortunate if (x+1) != (x+1L), as will 
happen with values bigger than 2^52.

Duncan Murdoch


> 
> 
> Benilton Carvalho
> 
> 
> 
> 
>> The double type in R can hold exact integer values up to around 2^52. So for
>> example calculations like this work fine:
>>
>>> x <- 2^50
>>> y <- x + 1
>>> y-x
>> [1] 1
>>
>> Just don't ask R to put those values into a 4 byte integer, they won't fit:
>>
>>> as.integer(c(x,y))
>> [1] NA NA
>> Warning message:
>> NAs introduced by coercion
>>
>> Duncan Murdoch
>>
>>> Glenn D Blanford, PhD
>>> <mailto:glenn.blanford at us.army.mil>
>>> Scientific Research Corporation
>>> gblanford at scires.com<mailto:gblanford at scires.com>
>>>
>>>
>>>        [[alternative HTML version deleted]]
>>>
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>> ______________________________________________
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>>