[datatable-help] unique

[Damian Betebenner]

Thanks Matthew

I was just trying something and saw this.

I can get what I want using unique with a data.frame. It gives the result one would expect.

This did make me somewhat scared that using a "by" statement with a data.table on multiple key might skip some unique combinations.

Damian 



Damian Betebenner
Center for Assessment
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Phone (office): (603) 516-7900
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dbetebenner at nciea.org
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-----Original Message-----
From: Matthew Dowle [mailto:mdowlenoreply at virginmedia.com] On Behalf Of Matthew Dowle
Sent: Saturday, June 25, 2011 8:27 PM
To: Damian Betebenner
Cc: datatable-help at lists.r-forge.r-project.org
Subject: Re: [datatable-help] unique

The NA in the key seems to be the issue. duplicated.data.table calls
diff on the columns and assumes no NA in keys.
Can't remember - did we decide to disallow NA in keys? There were other
issues with NA in keys and some threads in the past.
Do you need the key to contain NA?
Matthew


On Sat, 2011-06-25 at 16:23 -0500, Damian Betebenner wrote:
> All,
> 
>  
> 
> I have a simple question regarding the behavior of unique with more
> than 1 key. Consider the example:
> 
>  
> 
> > dt <- data.table(X=c(NA,1,2,3), Y=c(NA,2,1,3))
> 
> > dt
> 
>       X  Y
> 
> [1,] NA NA
> 
> [2,]  1  2
> 
> [3,]  2  1
> 
> [4,]  3  3
> 
> > key(dt) <- c("X", "Y")
> 
> > unique(dt)
> 
>       X  Y
> 
> [1,] NA NA
> 
> [2,]  2  1
> 
> [3,]  3  3
> 
>  
> 
> If I understand this correctly, unique see rows 2 and 3 of dt as the
> same. 
> 
>  
> 
> Is this the behavior one wants?
> 
>  
> 
> Thanks for any clarification.
> 
>  
> 
> Damian
> 
>  
> 
>  
> 
> 
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