[R] Logical operator fails to recognize vector element

[Duncan Murdoch]

  See FAQ 7.31.

Duncan Murdoch

On 06/10/2010 12:02 PM, D. Alain wrote:
> Hi experts,
>
> I have encountered a strange phenomenon after loading spreadsheet data via
>
> >example<-read.csv("M:\\...\\mydata.csv",header=T)
>
> My data consist of two variables x and y which I have combined to a single vector using
>
> >z<-rowSums(cbind(example$x,example$y))
> >z
> [1]  9.79  9.79 17.54 12.59  2.18  9.79 	#vector z with 6 elements
>
> Now I want to identify all elements equal to 9.79, so I enter
>
> >which(z==9.79)
>
> And I get the result
>
> [1] 2 6									#R failes to identify the fist element!
>
> Taking a futher look at the elements I get the following:
>
> >  mode(z)
> [1] "numeric"
> >  mode(z[1])
> [1] "numeric"
> >  z[1]+z[2]								#I can add first and second element
> [1] 19.58
>
> But if I try to apply logical operators I get:
>
> >  z[1]==9.79
> [1] FALSE
> >  z[2]==9.79
> [1] TRUE
> >  z[1]==z[2]
> [1] FALSE
>
> When I reenter the first element via
> >  z[1]<-9.79
> >  z[1]==9.79
> [1] TRUE
>
> What is wrong with my data? Can anyone help?
>
> >  version
>                 _
> platform         i386-pc-mingw32
> arch              i386
> os                 mingw32
> system          i386, mingw32
> status
> major             2
> minor            11.1
> year              2010
> month           05
> day               31
> svn rev           52157
> language        R
> version.string  R version 2.11.1 (2010-05-31)
>
> Thanks
> D. Alain
>
>
>
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