[R] unique and precision of long integers

[Uwe Ligges]

Michael Herron wrote:
> 
> Hello.
> 
> I have a dataset with about 500,000 observations, most of which are
> not unique.  The first 10 observations look like
> 
> 901000000000100000010100101011002
> 901101101110100000010100101011002
> 901000000000100000010100000001002
> 901000000000100000010101001011002
> 901000000000100000010101010011002
> 901000000000100000010100110101002
> 901000000000100000010100101011002
> 900000000000100000010010101011002
> 901000000000100000010100101101002
> 901000000000100000010100101011002
> 
> Each digit reflects a separate field, but above all spaces are
> removed.
> 
> I read in the data with scan(), and then use unique() to get the
> unique observations.  But, when I print these elements to a file I
> lose precision.  For instance, let x be a vector of the first 10
> observations from the dataset:
> 
> > write (x,file="output",ncol=1)
> 
> more output
> 
> 9.01e+32
> 9.011011e+32
> 9.01e+32
> 9.01e+32
> 9.01e+32
> 9.01e+32
> 9.01e+32
> 9e+32
> 9.01e+32
> 9.01e+32
> 
> Is there a way to get all the digits back?
> 
> > write (format(x,digits=22),file="output",ncol=1)
> 
> does not do it, and I cannot seem to increase digits >22.


Converting into characters should do the trick.


Uwe Ligges


BTW: You don't expect to get exact results calculating with such
numbers, do you?
If so, you have to think about some precision problems. Example:

> 90000000000000000000 == 90000000000000000001
[1] TRUE
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