[R] Help with abs function

[Jeff Newmiller]

FAQ 7.31
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Sent from my phone. Please excuse my brevity.

On June 12, 2015 8:39:48 AM PDT, "Nelson, Gary (MISC)" <gary.nelson at state.ma.us> wrote:
>I have come across some odd behavior (to me) using the abs() function
>that I wonder if anyone can explain.
>
>Using  R version 3.2.0, I created a vector of absolute values using 
>the following code:
>
>> tran<-c(7.2)
>> tgrid<-c(7.1,7.4,7.3,7.1,7.3)
>> dgrid<-abs(tgrid-tran)
>> dgrid
>[1] 0.1 0.2 0.1 0.1 0.1
>
>When I tried to extract just the rows with values>0.1, I get
>
>> dgrid[dgrid>0.1]
>[1] 0.1 0.2 0.1
>
>There should be only 1 value extracted.
>
>However, if I enter the values by hand
>
>> bgrid<-c(0.1,0.2,0.1,0.1,0.1)
>> bgrid
>[1] 0.1 0.2 0.1 0.1 0.1
>> bgrid[bgrid>0.1]
>[1] 0.2
>
>The result is correct.  So why is this happening?
>
>I did explore a little bit and found
>
>> as.character(dgrid)
>[1] "0.100000000000001"  "0.2"
>[3] "0.0999999999999996" "0.100000000000001"
>[5] "0.0999999999999996"
>
>which shows the absolute values of the negative differences  are
>slightly greater than the difference of 0.1
>
>Is this normal behavior for the abs() function?
>
>Thanks,
>
>Gary Nelson
>
>	[[alternative HTML version deleted]]
>
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