[R] rounding down with as.integer

[David Winsemius]

On Dec 31, 2014, at 3:24 PM, Mike Miller wrote:

> This is probably a FAQ, and I don't really have a question about it, but I just ran across this in something I was working on:
> 
>> as.integer(1000*1.003)
> [1] 1002
> 
> I didn't expect it, but maybe I should have.  I guess it's about the machine precision added to the fact that as.integer always rounds down:
> 
> 
>> as.integer(1000*1.003 + 255 * .Machine$double.eps)
> [1] 1002
> 
>> as.integer(1000*1.003 + 256 * .Machine$double.eps)
> [1] 1003
> 
> 
> This does it right...
> 
>> as.integer( round( 1000*1.003 ) )
> [1] 1003
> 
> ...but this seems to always give the same answer and it is a little faster in my application:
> 
>> as.integer( 1000*1.003 + .1 )
> [1] 1003
> 
> 
> FYI - I'm reading in a long vector of numbers from a text file with no more than three digits to the right of the decimal.  I'm converting them to integers and saving them in binary format.
> 

So just add 0.0001 or even .0000001 to all of them and coerce to integer.


> Best,
> Mike
> 
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David Winsemius
Alameda, CA, USA