Heinrich,
You could create your own function mywithin()
by inserting a couple of rev()'s in within.data.frame().
In within.data.frame(), replace the two commented lines
with those immediately following:
mywithin <-
function (data, expr, ...)
{
parent <- parent.frame()
# e <- evalq(environment(), data, parent)
e <- evalq(environment(), rev(data), parent)
eval(substitute(expr), e)
# l <- as.list(e)
l <- rev(as.list(e))
l <- l[!sapply(l, is.null)]
nD <- length(del <- setdiff(names(data), (nl <- names(l))))
data[nl] <- l
if (nD)
data[del] <- if (nD == 1)
NULL
else vector("list", nD)
data
}
Peter Ehlers
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?).
Thanks,
Heinrich.
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