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

[Ivan Calandra]

Hi Massimo,

Something along those lines could help you I guess:
t$A <- factor(t$A)
sapply(levels(t$A), function(x) which(t$A==x))

You can then play with the output using paste()

Ivan

--
Dr. Ivan Calandra
TraCEr, laboratory for Traceology and Controlled Experiments
MONREPOS Archaeological Research Centre and
Museum for Human Behavioural Evolution
Schloss Monrepos
56567 Neuwied, Germany
+49 (0) 2631 9772-243
https://www.researchgate.net/profile/Ivan_Calandra

On 06/06/2018 10:13, Massimo Bressan wrote:
> #given the following reproducible and simplified example
>
> t<-data.frame(id=1:10,A=c(123,345,123,678,345,123,789,345,123,789))
> t
>
> #I need to get the following result
>
> r<-data.frame(unique_A=c(123, 345, 678, 789),list_id=c('1,3,6,9','2,5,8','4','7,10'))
> r
>
> # i.e. aggregate over the variable "A" and list all elements of the variable "id" satisfying the criteria of having the same corrisponding value of "A"
> #any help for that?
>
> #so far I've just managed to "aggregate" and "count", like:
>
> library(sqldf)
> sqldf('select count(*) as count_id, A as unique_A from t group by A')
>
> library(dplyr)
> t%>%group_by(unique_A=A) %>% summarise(count_id = n())
>
> # thank you
>
>
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>
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