R help - Aug 2008 - Significant digits for checking values of variable?

FAQ 7.31

On Wed, Aug 27, 2008 at 11:51 AM, David Afshartous
<dafshartous at med.miami.edu> wrote:
>
> All,
>
> I'm witnessing some strange behavior when checking the values of one of
my
> variables.  My guess is that it has something to do with the number of
> significant digits being represented, but perhaps not as my variable was
> created from other variables that only had one decimal place.  See below.
> I'm sure this is something basic, any suggestions much appreciated.
>
> Cheers,
> David
>
>
>> visit.2.SEK.delta.baseline
>  [1]  0.1 -0.7  0.8 -0.1 -0.5  0.8  0.7  0.2  0.4  0.3  0.6  0.6  0.3  0.8
> 0.8  0.3  0.4  0.8
>> visit.2.SEK.delta.baseline > 0
>  [1]  TRUE FALSE  TRUE FALSE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE 
TRUE
> TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
>> visit.2.SEK.delta.baseline ==  .8
>  [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
FALSE
> FALSE FALSE FALSE FALSE FALSE FALSE
> ### but some of the values are equal to .8
>
> ## here it is okay when I try to reproduce
>>  junk = c(0.1, -0.7,0.8, -0.1, -0.5,  0.8,  0.7,  0.2,  0.4,  0.3, 
0.6,  0.6,
> 0.3,  0.8,  0.8,  0.3,  0.4,  0.8 )
>> junk == .8
>  [1] FALSE FALSE  TRUE FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE
FALSE
> FALSE  TRUE  TRUE FALSE FALSE  TRUE
>
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>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

All,

I'm witnessing some strange behavior when checking the values of one of my
variables.  My guess is that it has something to do with the number of
significant digits being represented, but perhaps not as my variable was
created from other variables that only had one decimal place.  See below.
I'm sure this is something basic, any suggestions much appreciated.

Cheers,
David

> visit.2.SEK.delta.baseline
 [1]  0.1 -0.7  0.8 -0.1 -0.5  0.8  0.7  0.2  0.4  0.3  0.6  0.6  0.3  0.8
0.8  0.3  0.4  0.8
> visit.2.SEK.delta.baseline > 0
 [1]  TRUE FALSE  TRUE FALSE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
> visit.2.SEK.delta.baseline ==  .8
 [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
FALSE FALSE FALSE FALSE FALSE FALSE
### but some of the values are equal to .8

## here it is okay when I try to reproduce
>  junk = c(0.1, -0.7,0.8, -0.1, -0.5,  0.8,  0.7,  0.2,  0.4,  0.3,  0.6, 
0.6,
0.3,  0.8,  0.8,  0.3,  0.4,  0.8 )
> junk == .8
 [1] FALSE FALSE  TRUE FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE
FALSE  TRUE  TRUE FALSE FALSE  TRUE