# create some test data
df <- data.frame( id=101:105, author_id=25:21, parent_id=c(NA,NA,101,NA,NA)
)
df$parent_author_id <- sapply(1:nrow(df),
function(i) { if( !is.na(df$parent_id[i]) ) { j <-
match(df$parent_id[i],df$id); df$author_id[j] } else NA } )
df
# id author_id parent_id parent_author_id
# 1 101 25 NA NA
# 2 102 24 NA NA
# 3 103 23 101 25
# 4 104 22 NA NA
# 5 105 21 NA NA
HTH,
Eric
On Sun, Jul 7, 2019 at 7:59 AM Alessandro Puglisi <
alessandro.pugl...@gmail.com> wrote:
> Hi all!
>
> I have a tibble regarding a series of comments on a forum; the tibble has a
> certain number of variables, and in particular:
>
> id: comment id;
> author_id: author id;
> parent_id: if the message is a reply, the original comment id
>
> I want to add another column, in which I put the author id of the original
> comment, when parent_id IS NOT NA.
>
> I already tried to use mutate + ifelse but my problem is that I have to
> refer to an author id in a different row than that in which I'm evaluating
> the if condition...
>
> Thanks in advance,
> Alessandro
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
