Hi
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Marine
> Regis
> Sent: Thursday, June 30, 2016 12:32 AM
> To: r-help at r-project.org
> Subject: [R] data.table: ?group counter? with NAs
>
> Hello,
>
> I would like to add a counter column in a data frame based on a set of
> identical rows. To do this, I tested:
>
> DF =
data.table(x=c("a","a","a","b","c","d","e","f","f"),
> y=c(1,3,2,8,8,4,NA,NA,NA))
>
> DF[ , Index := .GRP, by = c("y") ]
>
> DF
>
>
>
> However, the rows with NAs are considered to be identical.
Why they shall not be considered identical if you consider rows 4 and 5
identical?
You can do
DF[ , Index := .GRP, by = c("x","y") ]
But in that case rows 4 and 5 are NOT identical.
So you should state your rules for identical rows a little bit more clearly.
Cheers
Petr
>
> So, how can I obtain:
>
> x y Index
>
> 1: a 1 1
>
> 2: a 3 2
>
> 3: a 2 3
>
> 4: b 8 4
>
> 5: c 8 4
>
> 6: d 4 5
>
> 7: e NA 6
>
> 8: f NA 7
>
> 9: f NA 8
>
>
>
> Instead of:
>
> x y Index
>
> 1: a 1 1
>
> 2: a 3 2
>
> 3: a 2 3
>
> 4: b 8 4
>
> 5: c 8 4
>
> 6: d 4 5
>
> 7: e NA 6
>
> 8: f NA 6
>
> 9: f NA 6
>
>
>
>
>
> Thank you very much for your time.
>
> Have a nice day
>
> Marine
>
>
> [[alternative HTML version deleted]]
>
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