R help - Feb 2011 - Problem with long number (from character to numeric class)

Hello,

I have a text file with one column containing long number but stored as
string.
I download the file with read.table (and colClass) and the first row of this
column is :

"095842087016731010"

As I need to make some calculations with these numbers, I tried to convert
them using as.numeric.
But then I get
as.numeric("095842087016731010")
95842087016731008

I understand the disappearing of the first 0 but I don't understand the
substitution of the last 0 by 8.

Is there a way to avoid that ?
Thanks in advance,
Ptit Bleu. 
-- 
View this message in context:
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Sent from the R help mailing list archive at Nabble.com.

PtitBleu <ptit_bleu <at> yahoo.fr> writes:
> I have a text file with one column containing long number but stored as
> string.
> I download the file with read.table (and colClass) and the first row of
this
> column is :
> 
> "095842087016731010"
> 
> As I need to make some calculations with these numbers, I tried to convert
> them using as.numeric.
> But then I get
> as.numeric("095842087016731010")
> 95842087016731008
> 
  I think you are running into the limitations of double precision
values.  Take a look at the inverse of your value and compare it
to the "eps" values in .Machine.  Then see the R wiki (search for
"precision") for alternatives for extended precision calculations.

  Ben Bolker

On Feb 9, 2011, at 6:15 AM, PtitBleu wrote:
> 
> Hello,
> 
> I have a text file with one column containing long number but stored as
> string.
> I download the file with read.table (and colClass) and the first row of
this
> column is :
> 
> "095842087016731010"
> 
> As I need to make some calculations with these numbers, I tried to convert
> them using as.numeric.
> But then I get
> as.numeric("095842087016731010")
> 95842087016731008
> 
> I understand the disappearing of the first 0 but I don't understand the
> substitution of the last 0 by 8.
> 
> Is there a way to avoid that ?
> Thanks in advance,
> Ptit Bleu. 
I get:
> as.numeric("095842087016731010")
[1] 9.584209e+16

# See ?as.character
> as.character(as.numeric("095842087016731010"))
[1] "95842087016731008"


I suspect you would need to look at using one of the R packages that support
arbitrary/infinite precision representations if you need to deal with very large
integers. Perhaps look at gmp and Rmpfr.

You are hitting R's limit of 15 significant digits, resulting in the loss of
precision in the internal representation of the number, which is in turn,
presented in the resultant coercion.

HTH,

Marc Schwartz

FAQ 7.31

For 'numerics' there is a limit of about 15 digits of accuracy in the
number.

On Wed, Feb 9, 2011 at 7:15 AM, PtitBleu <ptit_bleu at yahoo.fr>
wrote:
>
> Hello,
>
> I have a text file with one column containing long number but stored as
> string.
> I download the file with read.table (and colClass) and the first row of
this
> column is :
>
> "095842087016731010"
>
> As I need to make some calculations with these numbers, I tried to convert
> them using as.numeric.
> But then I get
> as.numeric("095842087016731010")
> 95842087016731008
>
> I understand the disappearing of the first 0 but I don't understand the
> substitution of the last 0 by 8.
>
> Is there a way to avoid that ?
> Thanks in advance,
> Ptit Bleu.
> --
> View this message in context:
http://r.789695.n4.nabble.com/Problem-with-long-number-from-character-to-numeric-class-tp3297121p3297121.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?

On Feb 9, 2011, at 7:15 AM, PtitBleu wrote:
>
> Hello,
>
> I have a text file with one column containing long number but stored  
> as
> string.
> I download the file with read.table (and colClass) and the first row  
> of this
> column is :
>
> "095842087016731010"
>
> As I need to make some calculations with these numbers, I tried to  
> convert
> them using as.numeric.
> But then I get
> as.numeric("095842087016731010")
> 95842087016731008
Your number is many powers of ten above the maximum possible integer  
value 2*10^9. So you are seeing the floating point number that  
resulted from coercion, and R does not have arbitrary precision  
arithmetic in its base repertoire.
> I understand the disappearing of the first 0 but I don't understand  
> the
> substitution of the last 0 by 8.
>
> Is there a way to avoid that ?
There is a package that handles bignums, Brobdingnag.
. And there is interfaces to the symbolic algebra system, Yacas.  
But.... Do you really need arbitrary precision?

> Thanks in advance,
> Ptit Bleu.
> -- 

David Winsemius, MD
West Hartford, CT

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at
r-project.org]
> On Behalf Of PtitBleu
> Sent: Wednesday, February 09, 2011 4:15 AM
> To: r-help at r-project.org
> Subject: [R] Problem with long number (from character to numeric class)
> 
> 
> Hello,
> 
> I have a text file with one column containing long number but stored as
> string.
> I download the file with read.table (and colClass) and the first row of
> this
> column is :
> 
> "095842087016731010"
> 
> As I need to make some calculations with these numbers, I tried to convert
> them using as.numeric.
> But then I get
> as.numeric("095842087016731010")
> 95842087016731008
> 
> I understand the disappearing of the first 0 but I don't understand the
> substitution of the last 0 by 8.
> 
> Is there a way to avoid that ?
> Thanks in advance,
What kind of processing do you need to do with these numbers?  There may be
better ways to handle the problem.

Dan

Daniel Nordlund
Bothell, WA USA