[R] aggregate and list elements of variables in data.frame

[Bert Gunter]

which() is unnecessary. Use logical subscripting:

... t$id[t$A ==x]

Further simplification can be gotten by using the with() function:

l <- with(t, sapply(unique(A), function(x) id[A ==x]))

Check this though -- there might be scoping issues.

Cheers,
Bert



On Thu, Jun 7, 2018, 6:49 AM Massimo Bressan <massimo.bressan using arpa.veneto.it>
wrote:

> #ok, finally this is my final "best and more compact" solution of the
> problem by merging different contributions (thanks to all indeed)
>
> t<-data.frame(id=c(18,91,20,68,54,27,26,15,4,97),A=c(123,345,123,678,345,123,789,345,123,789))
>
> l<-sapply(unique(t$A), function(x) t$id[which(t$A==x)])
> r<-data.frame(unique_A= unique(t$A), list_id=unlist(lapply(l, paste,
> collapse = ", ")))
> r
>
>
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