Hello all, I'm trying to transform data frames by grouping the rows by the
values in a particular column, ordered by another column, then picking the
first row in each group.
I'd like to convert a data frame like this:
x y z
1 10 20
1 11 19
2 12 18
4 13 17
into one with three rows, like this, where i've discarded one row:
x y z
1 1 11 19
2 2 12 18
4 4 13 17
I've got a solution using aggregate, but it gets very slow with any volume
of data - the performance seems mostly IO bound and never finishes with a
data set ~6MB
Here's how I'm currently trying to do this
d = data.frame(x=c(1,1,2,4),y=c(10,11,12,13),z=c(20,19,18,17))
d.ordered = d[order(-d$y),]
aggregate(d.ordered,by=list(key=d.ordered$x),FUN=function(x){x[1]})
I've tried to use split and unsplit, but unsplit complained about duplicate
row names when reassembling the sub frames.
thanks for your suggestions
-james
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list
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.
