Weird error in R when importing (64-bit) integer with many digits

Question

I am importing a csv that has a single column which contains very long integers (for example: 2121020101132507598)

a<-read.csv('temp.csv',as.is=T)

When I import these integers as strings they come through correctly, but when imported as integers the last few digits are changed. I have no idea what is going on...

1 "4031320121153001444" 4031320121153001472
2 "4113020071082679601" 4113020071082679808
3 "4073020091116779570" 4073020091116779520
4 "2081720101128577687" 2081720101128577792
5 "4041720081087539887" 4041720081087539712
6 "4011120071074301496" 4011120071074301440
7 "4021520051054304372" 4021520051054304256
8 "4082520061068996911" 4082520061068997120
9 "4082620101129165548" 4082620101129165312

Answer 1

As others have noted, you can't represent integers that large. But R isn't reading those values into integers, it's reading them into double precision numerics.

Double precision can only represent numbers to ~16 places accurately, which is why you see your numbers rounded after 16 places. See the gmp, Rmpfr, and int64 packages for potential solutions. Though I don't see a function to read from a file in any of them, maybe you could cook something up by looking at their sources.

UPDATE: Here's how you can get your file into an int64 object:

# This assumes your numbers are the only column in the file
# Read them in however, just ensure they're read in as character
a <- scan("temp.csv", what="")
ia <- as.int64(a)

Answer 2

R's maximum intger value is about 2E9. As @Joshua mentions in another answer, one of the potential solutions is the int64 package.

Import the values as character instead. Then convert to type int64.

require(int64)
a <- read.csv('temp.csv', colClasses = 'character', header=FALSE)[[1]]
a <- as.int64(a)
print(a)
[1] 4031320121153001444 4113020071082679601 4073020091116779570
[4] 2081720101128577687 4041720081087539887 4011120071074301496
[7] 4021520051054304372 4082520061068996911 4082620101129165548

Answer 3

You simply cannot represent integers that big. See

.Machine

which on my box has

$integer.max
[1] 2147483647

Answer 4

The maximum value of a 32-bit signed integer is 2,147,483,647. Your numbers are much larger.

Try importing them as floating point values instead.

There4 are a few caveats to be aware of when dealing with floating point arithmetic in R or any other language:

http://blog.revolutionanalytics.com/2009/11/floatingpoint-errors-explained.html

http://blog.revolutionanalytics.com/2009/03/when-is-a-zero-not-a-zero.html

http://floating-point-gui.de/basic/