[datatable-help] Subsetting By Row Function

[PARIS Nicolas]

Hello Ben,

What about ordering on group+date descending, then removing duplicated
on group ?

someting like :
DT[!duplicated(Group),][order(Group,asDate(Date,format="yourFormat"),decreasing=T)]


Le 19/07/2014 00:40, bgoldstein a écrit :
> I am having trouble defining (and therefore searching) for this problem. I
> have data like this:
> 
> Group Value Date
> 1         xxx   June
> 1         yyy   July
> 2         zzzz   May
> 2         qqqq  August
> etc.
> 
> 
> I want to subset the 'Value' of each 'Group' by the latest 'Date'. So my
> output should be:
> 
> Group Value Date
> 1         yyy   July
> 2         qqqq  August
> etc.
> 
> The doBy package has a firstobs() function that works but is quite slow.
> 
> What would be a data.table way to do this?
> 
> Thank you,
> 
> Ben
> 
> 
> 
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