On 9/2/2009 9:27 AM, RINNER Heinrich wrote:
Dear R community,
I am using function 'within' in R.2.9.1 to add variables to an existing
data.frame. This works wonderful, except for one minor point: The new variables
are added to the data in reverse order.
For example:
x <- data.frame(a = 1:3, b = 4:6)
y <- within(x, {
c = a^2
d = b^2
e = c+d
}
)
gives
a b e d c
1 1 4 17 16 1
2 2 5 29 25 4
3 3 6 45 36 9
Just what I want; except that I would prefer the columns to be in order
a,b,c,d,e instead.
I could use transform ("transform(x, c=a^2, d=b^2, e=c+d)"), which preserves the
specified order of variables, but that won't work here because unfortunately it doesn't find object
'd' (same with "within(x, {e = c+d; d = b^2; c = a^2})", by the way).
Of course in my toy example I can easily do something like y[, c(1:2,5:3)]
afterwards, but I'd like to ask if maybe there is a simple way to make 'within'
preserve the order of specified variables (or maybe someone can shed light on
why this is not possible?).
Environments have no defined order, so you should not expect the order
of evaluations which create new variables to produce them in a
reproducible order.
To get the order you want, declare it from the beginning when you create
the data.frame. Or if x came from somewhere else, you could do this by
adding the new columns first, then modifying them:
x <- data.frame(a = 1:3, b = 4:6) # original creation
x <- data.frame(x, c=1,d=1,e=1) # add some new columns
y <- within(x, { # modify them
c = a^2
d = b^2
e = c+d
}
)
Duncan Murdoch
______________________________________________
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.
