Entering numbers with decimals

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Entering numbers with decimals

Mike Leahy
Hello list,

I'm just getting started with R, and I'm trying to determine how R
treats large numbers that have decimals.  Take the following two examples:

> x <- c(999999999999999.9)
> sprintf("%.5f",x)
[1] "999999999999999.87000"

> y <- c(9999999999999999.9)
> sprintf("%.5f",y)
[1] "10000000000000000.00000"

I realize that I have no idea what I'm doing as far as using R is
concerned, but maybe someone can tell me what would be the best way to
input/output numbers such that they don't get rounded off in unexpected
ways.  I've been searching online and looking through various R manuals,
but I haven't found anything that really clarifies this so far...

Thanks in advance for any advice,

Mike

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Re: Entering numbers with decimals

Duncan Murdoch
On 4/8/2006 3:51 PM, Mike Leahy wrote:

> Hello list,
>
> I'm just getting started with R, and I'm trying to determine how R
> treats large numbers that have decimals.  Take the following two examples:
>
>> x <- c(999999999999999.9)
>> sprintf("%.5f",x)
> [1] "999999999999999.87000"
>
>> y <- c(9999999999999999.9)
>> sprintf("%.5f",y)
> [1] "10000000000000000.00000"
>
> I realize that I have no idea what I'm doing as far as using R is
> concerned, but maybe someone can tell me what would be the best way to
> input/output numbers such that they don't get rounded off in unexpected
> ways.  I've been searching online and looking through various R manuals,
> but I haven't found anything that really clarifies this so far...

R uses standard double precision storage for floating point numbers,
which means approximately 15-16 decimal place accuracy.  There isn't
anything you can easily do to improve this in general, though the gmp
package allows some calculations to high precision.

Duncan Murdoch

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