[R] %in% not working

[Barry Rowlingson]

Neil Klepeis wrote:
> Thanks to Thomas and everyone on my floating point confusion,
> 
> Is there any reason why conversion to 'character' wouldn't be the safest 
> way to compare decimal numbers:
> 
>  > 1.253 %in% seq(1.1,1.3,by=0.001)
> [1] FALSE
>  > 1.253 %in% as.character(seq(1.1,1.3,by=0.001))
> [1] TRUE
>  > 0.001 %in% 1E-3
> [1] TRUE
>  > "0.001" %in% "1E-3"
> [1] FALSE
>  > as.character(0.001) %in% as.character(1E-3)
> [1] TRUE

  Impressive, but:

 > as.character(1e-4) == as.character(0.0001+.000000000000000000000001)
[1] TRUE

  - as.character gets it wrong -

  Wheras:

 > 1e-4 == 0.0001+.0000000000000000001
[1] FALSE

  - plain old numbers gets it right.

  Far better to understand what is going on with floating point numbers 
and their inherent imprecision, and then work round it!

Baz

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