Hello dear R-help group.

My task looks simple, but I can't seem to find a "smart" (e.g: non loop)
solution to it.

Task: I wish to randomize a data.frame by one column, while keeping the
inner-order in the second column as is.

So for example, let's say I have the following data.frame:

xx <-data.frame(a=  c(1,2,2,3,3,3,4,4,4,4) ,
                        b =  c(1,1,2,1,2,3,1,2,3,4) )

I would like to shuffle it by column "a", while keeping the order in column
"b".

Here is my "not-smart" way of doing it:

# R example
xx <-data.frame(a=  c(1,2,2,3,3,3,4,4,4,4) ,
                        b =  c(1,1,2,1,2,3,1,2,3,4) )

randomize.by.column.a <- function(xx)
{
new.a.order <- sample(unique(xx$a))
new.xx <- NULL
for(i in new.a.order)
{
  xx.subset <- xx[ xx$a %in% i ,]
  new.xx <- rbind(new.xx ,  xx.subset)
}

return(new.xx)
}
randomize.by.column.a(xx)
# END of - R example



I would love for a better, faster, way of doing it.

Thanks,
Tal










-- 
----------------------------------------------


My contact information:
Tal Galili
Phone number: 972-50-3373767
FaceBook: Tal Galili
My Blogs:
http://www.r-statistics.com/
http://www.talgalili.com
http://www.biostatistics.co.il

	[[alternative HTML version deleted]]


