On 5/27/2009 8:39 AM, Paul Geeleher wrote:
I've got a matrix with 2 columns and n rows. I need to sort it first
by the values in column 1 ascending. Then for values which are the
same in column 1, sort by column 2 decending. For example:
You've seen a few ways. Here are some more:
1. Use the fact that order() uses a stable sort algorithm, so just sort
by the second column then the first:
x <- matrix(c(2,1,1,3,.5,.3,.5,.2), ncol=2)
x1 <- x[order(x[,2], decreasing=TRUE),]
x2 <- x1[order(x1[,1]),]
x2
2. Use the fact that your values are numeric, so negatives sort in the
reverse order of positives:
x[order(x[,1], -x[,2]),]
3. If the values aren't known to be numeric, convert them to numeric
before using them as sort keys:
x[order(xtfrm(x[,1]), -xtfrm(x[,2])),]
In any of these, watch out for NA handling. My methods all put NA
values last, but that might not be what you want.
Duncan Murdoch
2 .5
1 .3
1 .5
3 .2
Goes to:
1 .5
1 .3
2 .5
3 .2
This is easy to do in spreadsheet programs but I can't seem to work
out how to do it in R and haven't been able to find a solution
anywhere.
Thanks!
-Paul.
______________________________________________
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.
