[R] About basic logical operators

[Duncan Murdoch]

On 05/03/2013 7:53 PM, Victor hyk wrote:
> Hello everyone,
>            I have a basic question regarding logical operators.
> > x<-seq(-1,1,by=0.02)
> > x
>    [1] -1.00 -0.98 -0.96 -0.94 -0.92 -0.90 -0.88 -0.86 -0.84 -0.82 -0.80 -0.78
>   [13] -0.76 -0.74 -0.72 -0.70 -0.68 -0.66 -0.64 -0.62 -0.60 -0.58 -0.56 -0.54
>   [25] -0.52 -0.50 -0.48 -0.46 -0.44 -0.42 -0.40 -0.38 -0.36 -0.34 -0.32 -0.30
>   [37] -0.28 -0.26 -0.24 -0.22 -0.20 -0.18 -0.16 -0.14 -0.12 -0.10 -0.08 -0.06
>   [49] -0.04 -0.02  0.00  0.02  0.04  0.06  0.08  0.10  0.12  0.14  0.16  0.18
>   [61]  0.20  0.22  0.24  0.26  0.28  0.30  0.32  0.34  0.36  0.38  0.40  0.42
>   [73]  0.44  0.46  0.48  0.50  0.52  0.54  0.56  0.58  0.60  0.62  0.64  0.66
>   [85]  0.68  0.70  0.72  0.74  0.76  0.78  0.80  0.82  0.84  0.86  0.88  0.90
>   [97]  0.92  0.94  0.96  0.98  1.00
> > x[x<=0.02]
>   [1] -1.00 -0.98 -0.96 -0.94 -0.92 -0.90 -0.88 -0.86 -0.84 -0.82 -0.80 -0.78
> [13] -0.76 -0.74 -0.72 -0.70 -0.68 -0.66 -0.64 -0.62 -0.60 -0.58 -0.56 -0.54
> [25] -0.52 -0.50 -0.48 -0.46 -0.44 -0.42 -0.40 -0.38 -0.36 -0.34 -0.32 -0.30
> [37] -0.28 -0.26 -0.24 -0.22 -0.20 -0.18 -0.16 -0.14 -0.12 -0.10 -0.08 -0.06
> [49] -0.04 -0.02  0.00
> > x[x<0.2]
>   [1] -1.00 -0.98 -0.96 -0.94 -0.92 -0.90 -0.88 -0.86 -0.84 -0.82 -0.80 -0.78
> [13] -0.76 -0.74 -0.72 -0.70 -0.68 -0.66 -0.64 -0.62 -0.60 -0.58 -0.56 -0.54
> [25] -0.52 -0.50 -0.48 -0.46 -0.44 -0.42 -0.40 -0.38 -0.36 -0.34 -0.32 -0.30
> [37] -0.28 -0.26 -0.24 -0.22 -0.20 -0.18 -0.16 -0.14 -0.12 -0.10 -0.08 -0.06
> [49] -0.04 -0.02  0.00  0.02  0.04  0.06  0.08  0.10  0.12  0.14  0.16  0.18
> [61]  0.20
> >
>       Why does "x[x<=0.02]" return  no 0.02

You don't have a 0.02 in your dataset.  Evaluate x[52] - 0.02 and you 
won't get zero due to rounding (as Jeff said, see FAQ 7.31).
> but "x[x<0.2]" return a subsample with 0.02?

You don't have 0.2, either.  Evaluate x[61] - 0.2 and you get a negative 
value.

Duncan Murdoch

>       Anyone who can tell me why?
>       Thanks!
>
>       Victor
>
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>
>
>
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