[R] numeric not equal its value

[Clint Bowman]

Jannis,

Not strange.  Try with numbers that can be exactly represented in binary 
(that's what computers use), e.g.,

a<-seq(5,70,by=5)
b<-15
a==b

or fractions,

a<-seq(1/32,14/32,by=1/32)
b<-3/32
a==b

Most decimal fractions cannot be represented exactly although a bit of 
magic will display them as if they are.

A little digging into the r-help archives will find further explanation.

Clint

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On Mon, 20 May 2013, Jannis wrote:

> Dear R users,
>
>
>
> I ran into the strange situation where a number does not seem to equal its 
> value. Try this:
>
>
>
> a <- seq(0.05,0.7,0.05)[3]
>
> b <- 0.15
>
> a == b
>
>
> Should this not be TRUE? a-b yields a very small number (and not 0) so this 
> most probably is a numerical error, but why does seq create such numbers?
>
>
> Thanks a lot
> Jannis
>
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