On 21/05/2013 12:19, D. Rizopoulos wrote:
Dear All,
I'm interested in creating a function similar to ns() from package
splines that can be passed in a model formula. The idea is to produce
"safe" predictions from a model using this function. As I have seen, to
do this I need to use makepredictcall(). Consider the following toy example:
myns <- function (x, df = NULL, knots = NULL, intercept = FALSE,
Boundary.knots = range(x),
extraArg = 0) {
ns.x <- if (is.null(knots)) {
ns(x, df = df, intercept = intercept, Boundary.knots =
Boundary.knots)
} else {
ns(x, knots = knots, intercept = intercept, Boundary.knots =
Boundary.knots)
}
out <- ns.x + extraArg
attr(out, "class") <- c("myns", "basis", "matrix")
out
}
makepredictcall.myns <- function (var, call) {
# based on splines:::makepredictcall.ns
if (as.character(call)[1L] != "myns")
return(call)
at <- attributes(var)[c("knots", "Boundary.knots", "intercept",
"extraArg")]
xxx <- call[1L:2L]
xxx[names(at)] <- at
xxx
}
dd <- data.frame(y = rnorm(12))
terms(model.frame(terms(~ myns(y, df = 3, extraArg = 0.5)), data = dd))
As it can be seen, makepredictcall.myns() succeeds in correctly passing
the knots and Boundary.knots from the original data in the "predvars"
attribute of the terms objects but it does not work for the new argument
'extraArg' I introduced in myns().
Well, you did not set that attribute in myns(), but you looked for it.
I guess you intended
myns <- function (x, df = NULL, knots = NULL, intercept = FALSE,
Boundary.knots = range(x),
extraArg = 0) {
ns.x <- if (is.null(knots)) {
ns(x, df = df, intercept = intercept, Boundary.knots =
Boundary.knots)
} else {
ns(x, knots = knots, intercept = intercept, Boundary.knots =
Boundary.knots)
}
out <- ns.x + extraArg
attr(out, "extraArg") <- extraArg
attr(out, "class") <- c("myns", "basis", "matrix")
out
}
Any pointers on how to resolve this will be highly appreciated.
Thanks in advance.
Best,
Dimitris
--
Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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